The Danish National Birth Cohort--its background, structure and aim

Body mass index, waist circumference, and urinary incontinence in midlife: A follow-up of mothers in the Danish National Birth Cohort

BACKGROUND

Obesity is a modifiable risk factor for urinary incontinence, yet few studies have investigated how waist circumference as compared to body mass index (BMI) influences the risk of urinary incontinence.

OBJECTIVE

To estimate how BMI and waist circumference associates with risk of urinary incontinence in midlife and determine which of the two is the strongest predictor of urinary incontinence.

METHODS

Cohort study among mothers in the Danish National Birth Cohort. Weight and waist circumference were self-reported 7 years after cohort entry. Symptoms of urinary incontinence in midlife were self-reported using the International Consultation on Incontinence Questionnaire Female Lower Urinary Tract Symptoms (ICIQ-FLUTS) and analyzed continuously and as presence or absence of any, stress (SUI), urgency (UUI), and mixed (MUI) urinary incontinence. Linear and log binomial regressions were used to calculate mean differences and risk ratios (RR) with 95% confidence intervals (CI). Restricted cubic splines were generated to explore nonlinear relationships.

RESULTS

Among 27 254 women at a mean age of 44.2 years, any urinary incontinence was reported by 32.1%, SUI by 20.9%, UUI by 2.4%, and MUI by 8.6%. For all outcomes, increases in risk were similar with higher BMI and waist circumference. The estimates of association were strongest for MUI (RR 1.10, 95% CI 1.08;1.12 and RR 1.12, 95% CI 1.10;1.14 for half a standard deviation increase in BMI and waist circumference, respectively). While increases in risk of the other outcomes were seen across the entire range of BMI and waist circumference, the risk of SUI rose until BMI 28 kg/m² (waist circumference 95 cm), and then fell slightly.

CONCLUSIONS

Symptoms of urinary incontinence and prevalence of any urinary incontinence, SUI, UUI, and MUI increased with higher BMI and waist circumference. Self-reported BMI and waist circumference were equally predictive of urinary incontinence.

A Review of Major Danish Biobanks: Advantages and Possibilities of Health Research in Denmark

Biobank research may lead to an improved understanding of disease etiology and advance personalized medicine. Denmark (population ~5.9 million) provides a unique setting for population-based health research. The country is a rich source of biobanks and the universal, tax-funded healthcare system delivers routinely collected data to numerous registries and databases. By virtue of the civil registration number (assigned uniquely to all Danish citizens), biological specimens stored in biobanks can be combined with clinical and demographic data from these population-based health registries and databases. In this review, we aim to provide an understanding of advantages and possibilities of biobank research in Denmark. As knowledge about the Danish setting is needed to grasp the full potential, we first introduce the Danish healthcare system, the Civil Registration System, the population-based registries, and the interface with biobanks. We then describe the biobank infrastructures, comprising the Danish National Biobank Initiative, the Bio- and Genome Bank Denmark, and the Danish National Genome Center. Further, we briefly provide an overview of fourteen selected biobanks, including: The Danish Newborn Screening Biobank; The Danish National Birth Cohort; The Danish Twin Registry Biobank; Diet, Cancer and Health; Diet, Cancer and Health - Next generations; Danish Centre for Strategic Research in Type 2 Diabetes; Vejle Diabetes Biobank; The Copenhagen Hospital Biobank; The Copenhagen City Heart Study; The Copenhagen General Population Study; The Danish Cancer Biobank; The Danish Rheumatological Biobank; The Danish Blood Donor Study; and The Danish Pathology Databank. Last, we inform on practical aspects, such as data access, and discuss future implications.

Exposures to pesticides and risk of cancer: Evaluation of recent epidemiological evidence in humans and paths forward

Knowledge of the role in cancer etiology of environmental exposures as pesticides is a prerequisite for primary prevention. We review 63 epidemiological studies on exposure to pesticides and cancer risk in humans published from 2017 to 2021, with emphasis on new findings, methodological approaches, and gaps in the existing literature. While much of the recent evidence suggests causal relationships between pesticide exposure and cancer, the strongest evidence exists for acute myeloid leukemia (AML) and colorectal cancer (CRC), diseases in which the observed associations were consistent across several studies, including high-quality prospective studies and those using biomarkers for exposure assessment, with some observing dose-response relationships. Though high-quality studies have been published since the IARC monograph on organophosphate insecticides in 2017, there are still gaps in the literature on carcinogenic evidence in humans for a large number of pesticides. To further knowledge, we suggest leveraging new techniques and methods to increase sensitivity and precision of exposure assessment, incorporate multi-omics data, and investigate more thoroughly exposure to chemical mixtures. There is also a strong need for better and larger population-based cohort studies that include younger and nonoccupationally exposed individuals, particularly during developmental periods of susceptibility. Though the existing evidence has limitations, as always in science, there is sufficient evidence to implement policies and regulatory action that limit pesticide exposure in humans and, hence, further prevent a significant burden of cancers.

Impact of a manager-oriented intervention on occupational exposures and well-being among pregnant hospital and day-care employees: A cluster randomised trial

BACKGROUND

Pregnancy can make it difficult to cope with demands at work and may affect women's well-being. We investigated if a manager-targeted educational intervention reduced demanding occupational exposures and improved the psychosocial work environment and well-being among pregnant employees.

METHODS

Data came from a cluster randomised trial in Danish hospitals and day-care institutions. Work units were assigned randomly and were non-blinded to the intervention, where managers were either invited to participate in a three-hour seminar addressing job adjustment in pregnancy or assigned to a control group undertaking their usual practice. Self-reported outcomes by pregnant employees at the work units were the proportion of pregnant employees with demanding occupational exposures, good psychosocial work environment and good well-being. Mixed logistic regression was applied in the population of responders and in intention-to-treat analyses using multiple imputations.

RESULTS

We included 915 pregnant employees: 451 in the intervention group and 464 in the control group. Of 216 invited managers, 103 (48%) participated in the seminar. A total of 339 (37%) pregnant employees answered the questionnaire. The proportion of pregnant employees who had demanding occupational exposures, good psychosocial work environment and good well-being in the intervention versus the control group were 36% versus 39% (odds ratio (OR)=0.90, 95% confidence interval (CI) 0.57-1.44), 56% versus 59% (OR=1.01, 95% CI 0.60-1.71) and 77% versus 73% (OR=1.13, 95% CI 0.68-1.87), respectively.

CONCLUSIONS

This manager-targeted educational intervention did not reduce demanding occupational exposures and did not improve the psychosocial work environment or the well-being among pregnant employees in hospital and day-care settings. Comprehensive and participatory interventions may be considered in future studies.

Maternal intake of folate and folic acid during pregnancy and markers of male fecundity: A population-based cohort study

BACKGROUND

Poor male fecundity is of concern, and a prenatal origin has been proposed. Folate, a methyl donor involved in DNA methylation, is essential for normal fetal development by regulating gene expression during different periods of fetal development. Thus, prenatal exposure to low maternal folate intake might have a programing function of the developing reproductive organs.

OBJECTIVES

To examine the association between maternal intake of folate from diet and folic acid from supplements during pregnancy and markers of fecundity in young men.

MATERIALS AND METHODS

We conducted a follow-up study using a Danish mother-son cohort of 787 young men born 1998-2000. Percentage differences in semen characteristics, testes volume, and reproductive hormone levels were analyzed according to total folate calculated as dietary folate equivalents from diet and supplements in midpregnancy, using multivariable negative binomial regression models. Total folate was analyzed in quintiles, continuous per standard deviation decrease (SD: 318 μg/day) and as restricted cubic splines.

RESULTS

Low maternal intake of total folate was associated with lower total sperm count (-5% (95% confidence intervals [CI]: -11%; 2%)), a lower proportion of non-progressive and immotile spermatozoa (-5% [95% CI: -8%; -3%]), and lower testes volume (-4% [95% CI: -6%; -2%]) per SD decrease in total folate intake. Spline plots supported these findings.

DISCUSSION

The finding of a lower proportion of non-progressive and immotile spermatozoa, and hence a higher proportion of motile spermatozoa, in men of mothers with a lower intake of total folate in midpregnancy was surprising and may be a chance finding.

CONCLUSION

Lower maternal intake of total folate in midpregnancy was associated with lower sperm count and lower testes volume, however, also with a lower proportion of non-progressive and immotile spermatozoa in adult men. Whether this actually affects the ability to obtain a pregnancy warrants further investigation.

Maternal fever during pregnancy and male offspring reproductive health: A longitudinal cohort study in young Danish males

BACKGROUND

Maternal fever during pregnancy has been associated with an increased risk of genital malformations, but the implication for long-term reproductive health in the offspring is unknown.

OBJECTIVES

To investigate associations between timing, duration, and temperature of fetal exposure to maternal fever and sons' semen quality, testicular volume, and levels of reproductive hormones in early adulthood. Further, to examine whether concurrent use of antipyretics and/or antibiotics modified the effect.

MATERIALS AND METHODS

We used the Fetal Programming of Semen Quality cohort consisting of men born to women enrolled in the Danish National Birth Cohort. Self-reported information on maternal fever was collected twice during pregnancy (median 16 and 31 pregnancy weeks) and categorized as any fever during pregnancy, fever during early pregnancy (weeks 1-15), and fever exclusively during late pregnancy (weeks 16-42). Semen quality and concentrations of reproductive hormones were measured at a clinical examination at the age of 18.9 years. We used negative binomial regression to examine the associations, adjusting for maternal age at birth, maternal smoking, family occupational status, and precision variables related to semen quality and hormonal levels, for example, abstinence time.

RESULTS

986 men were included in the study, of which 23% had mothers reporting at least one episode of fever. We found no strong indications of associations between maternal fever during pregnancy and male reproductive health in young men. Concurrent use of antipyretics and antibiotics did not modify the association.

DISCUSSION

Strengths include the large sample size, prospectively collected data, and the adjustment for maternal factors during pregnancy and important precision variables. A limitation is the crude self-reported information on maternal fever.

CONCLUSION

We found no evidence to support that timing, duration, or temperature of maternal fever during pregnancy has a long-term impact on semen characteristics, testicular volume, or level of reproductive hormones in male offspring.

Self-injury, suicidality and eating disorder symptoms in young adults following COVID-19 lockdowns in Denmark

An aggravation in mental health during the COVID-19 lockdown has been suggested but the impact on self-injury, suicidality and eating disorders (EDs) are less elucidated. Using linear regression in different data set-ups that is longitudinal (n = 7,579) and repeated cross-sectional data (n = 24,625) from the Danish National Birth Cohort, we compared self-reported self-injury, suicidality and symptoms of EDs from before through different pandemic periods until spring 2021. The longitudinal data indicate a reduction in the proportion of self-injury in men (-3.2% points, 95% confidence interval (CI) = -4.3%; -2.2%, P < 0.001, d.f. = 2) and women (5.7% points, 95% CI = -6.6%; -4.8%, P < 0.001, d.f. = 2) and of suicide ideation in men (-3.0% points, 95% CI = -4.6%; -1.4%, P = 0.002, d.f. = 2) and women (-7.4% points, 95% CI = -8.7%; -6.0%, P < 0.001, d.f. = 2), as well as symptoms of EDs in women (-2.3% points, 95% CI = -3.2%; -1.4%, P < 0.001, d.f. = 2). For suicide attempt, indication of an increase was observed in men only (0.4% points, 95% CI = 0.1%; 0.7%, P = 0.019, d.f. = 2). In the repeated cross-sectional data, we observed no changes in any of the outcomes. Our findings provide no support for the increase in self-injury, suicidality and symptoms of EDs after the lockdowns. Key limitations are differential attrition and varying age in pre- and post-lockdown measures in the longitudinal data.

Association of self-reported mother-infant relationship with child and adolescent mental health

BACKGROUND

The quality of the relationship between mother and infant may have profound implications for the development of a child. Early indicators of psychological vulnerability may allow targeting of support for the child's cognitive, emotional and social development. A challenging mother-infant relationship could be one indicator of risk.

AIMS

This study examined variations in psychological well-being and psychopathology among boys and girls according to early maternal perception of the mother-infant relationship.

METHOD

This study is based on 64 663 mother-infant pairs from the Danish National Birth Cohort, for which data on the mother-infant relationship were collected at 6 months postpartum. Behavioural problems were assessed with the Danish version of the Strengths and Difficulties Questionnaire (SDQ) at child ages 7, 11 and 18 years, and we retrieved information on diagnosed childhood and adolescent psychiatric disorders and prescriptions of psychotropic drugs from Danish registries.

RESULTS

Children in the challenging mother-infant relationship group had higher odds of behavioural problems at age 7 among both boys and girls. The same pattern of elevated estimates was identified for boys across all SDQ domains and for girls in three of five SDQ domains. All associations were attenuated at age 18, but increased odds of behavioural problems still existed. A challenging early mother-infant relationship increased the offspring's risk of being diagnosed with a psychiatric disorder or being prescribed a psychotropic drug before the age of 18.

CONCLUSION

A challenging self-reported mother-infant relationship was associated with later psychopathological difficulties. Routine clinical enquiry may be useful in identification of future vulnerability.

Selection bias in a male-offspring cohort investigating fecundity: is there reason for concern?

STUDY QUESTION

Is there risk of selection bias in etiological studies investigating prenatal risk factors of poor male fecundity in a cohort of young men?

SUMMARY ANSWER

The risk of selection bias is considered limited despite a low participation rate.

WHAT IS KNOWN ALREADY

Participation rates in studies relying on volunteers to provide a semen sample are often very low. Many risk factors for poor male fecundity are associated with participation status, and as men with low fecundity may be more inclined to participate in studies of semen quality, a risk of selection bias exists.

STUDY DESIGN, SIZE, DURATION

A population-based follow-up study of 5697 young men invited to the Fetal Programming of Semen Quality (FEPOS) cohort nested within the Danish National Birth Cohort (DNBC), 1998-2019.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Young men (age range: 18 years, 9 months to 21 years, 4 months) born 1998-2000 by mothers included in the DNBC were invited to participate in FEPOS. In total, 1173 men answered a survey in FEPOS (n = 115 participated partly); of those, 1058 men participated fully by also providing a semen and a blood sample at a clinical visit. Differential selection according to parental baseline characteristics in the first trimester, the sons' own characteristics from the FEPOS survey, and urogenital malformations and diseases in reproductive organs from the Danish registers were investigated using logistic regression. The influence of inverse probability of selection weights (IPSWs) to investigate potential selection bias was examined using a predefined exposure-outcome association of maternal smoking in the first trimester (yes, no) and total sperm count analysed using adjusted negative binomial regression. A multidimensional bias analysis on the same association was performed using a variety of bias parameters to assess different scenarios of differential selection.

MAIN RESULTS AND THE ROLE OF CHANCE

Participation differed according to most parental characteristics in first trimester but did not differ according to the prevalence of a urogenital malformation or disease in the reproductive organs. Associations between maternal smoking in the first trimester and male fecundity were similar when the regression models were fitted without and with IPSWs. Adjusting for other potential risk factors for poor male fecundity, maternal smoking was associated with 21% (95% CI: -32% to -9%) lower total sperm count. In the bias analysis, this estimate changed only slightly under realistic scenarios. This may be extrapolated to other exposure-outcome associations.

LIMITATIONS, REASONS FOR CAUTION

We were unable to directly assess markers of male fecundity for non-participants from, for example an external source and therefore relied on potential proxies of fecundity. We did not have sufficient power to analyse associations between prenatal exposures and urogenital malformations.

WIDER IMPLICATIONS OF THE FINDINGS

The results are reassuring when using this cohort to identify causes of poor male fecundity. The results may be generalized to other similar cohorts. As the young men grow older, they can be followed in the Danish registers, as an external source, to examine, whether participation is associated with the risk of having an infertility diagnosis.

STUDY FUNDING/COMPETING INTEREST(S)

The project was funded by the Lundbeck Foundation (R170-2014-855), the Capital Region of Denmark, Medical doctor Sofus Carl Emil Friis and spouse Olga Doris Friis's Grant, Axel Muusfeldt's Foundation (2016-491), AP Møller Foundation (16-37), the Health Foundation, Dagmar Marshall's Fond, Aarhus University and Independent Research Fund Denmark (9039-00128B). The authors declare that they have no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

New insights from the last decade of research in psychiatric genetics: discoveries, challenges and clinical implications

Psychiatric genetics has made substantial progress in the last decade, providing new insights into the genetic etiology of psychiatric disorders, and paving the way for precision psychiatry, in which individual genetic profiles may be used to personalize risk assessment and inform clinical decision-making. Long recognized to be heritable, recent evidence shows that psychiatric disorders are influenced by thousands of genetic variants acting together. Most of these variants are commonly occurring, meaning that every individual has a genetic risk to each psychiatric disorder, from low to high. A series of large-scale genetic studies have discovered an increasing number of common and rare genetic variants robustly associated with major psychiatric disorders. The most convincing biological interpretation of the genetic findings implicates altered synaptic function in autism spectrum disorder and schizophrenia. However, the mechanistic understanding is still incomplete. In line with their extensive clinical and epidemiological overlap, psychiatric disorders appear to exist on genetic continua and share a large degree of genetic risk with one another. This provides further support to the notion that current psychiatric diagnoses do not represent distinct pathogenic entities, which may inform ongoing attempts to reconceptualize psychiatric nosology. Psychiatric disorders also share genetic influences with a range of behavioral and somatic traits and diseases, including brain structures, cognitive function, immunological phenotypes and cardiovascular disease, suggesting shared genetic etiology of potential clinical importance. Current polygenic risk score tools, which predict individual genetic susceptibility to illness, do not yet provide clinically actionable information. However, their precision is likely to improve in the coming years, and they may eventually become part of clinical practice, stressing the need to educate clinicians and patients about their potential use and misuse. This review discusses key recent insights from psychiatric genetics and their possible clinical applications, and suggests future directions.

Design and Progress of Child Health Assessments at Community Support Centers in the Birth and Three-Generation Cohort Study of the Tohoku Medical Megabank Project

The Tohoku Medical Megabank Project (TMM) has been conducting a birth and three-generation cohort study (the BirThree Cohort Study). We recruited 73,529 pregnant women and their family members for this cohort study, which included 23,143 newborns and 9,459 of their siblings. We designed and are in the process of conducting three-step health assessments for each newborn at approximately ages of 5, 10 and 16. These health assessments are administered at seven community support centers. Trained genome medical research coordinators conduct physical examinations of and collect biological specimens from each participant. The Sendai Children's Health Square has been established as the headquarters for these child health assessments and is utilized to accumulate knowledge that can facilitate the proper practice of child health assessments. We designed all the relevant health assessments facilities to allow parents and their children to participate in the health assessments concomitantly. Our centers serve as places where child participants and their parents can feel at ease as a result of the implementation of safety measures and child hospitality measures. The TMM BirThree Cohort Study is in the process of conducting strategically detailed health assessments and genome analysis, which can facilitate studies concerning the gene-environment interactions relevant to noncommunicable diseases. Through these operations, our study allows for a significant depth of data to be collected in terms of the number of biospecimens under study and the comprehensiveness of both basic and clinical data alongside relevant family information.

Maternal age at menarche and reproductive health in young adult men: a cohort study

STUDY QUESTION

Is maternal age at menarche associated with reproductive health in sons measured by semen quality, testes volume and reproductive hormone levels?

SUMMARY ANSWER

Later maternal age at menarche was associated with impaired semen characteristics, lower testes volume and altered levels of reproductive hormones, while earlier maternal age at menarche was not strongly associated with reproductive outcomes in sons.

WHAT IS KNOWN ALREADY

Both earlier and later maternal age at menarche may be associated with altered male reproductive health outcomes. This is the first study to investigate the potential association between maternal age at menarche and semen quality, testes volume and reproductive hormone levels in sons.

STUDY DESIGN, SIZE, DURATION

In this population-based cohort study, we used data from the Fetal Programming of Semen Quality Cohort nested within the Danish National Birth Cohort. In total, 5697 sons born in 1998-2000 were invited to participate in the cohort in 2017-2019.

PARTICIPANTS/MATERIALS, SETTING, METHODS

In total, 1043 (18% of the invited) young men with information on maternal age at menarche provided a semen and blood sample, measured their testes volume, and filled in a questionnaire on health behavior and pubertal development. Maternal age at menarche was reported by the mothers during pregnancy and examined categorically (as earlier, at the same time or later than their peers), continuously and modeled as splines. We estimated relative percentage differences in the reproductive outcomes using negative binomial regression models. Further, we did a mediation analysis to investigate the potential mediating role of timing of the sons' pubertal development.

MAIN RESULTS AND THE ROLE OF CHANCE

Sons whose mothers had age at menarche later than peers had 15% lower (95% CI: -27%; 0%) sperm concentration, 14% lower (95% CI: -28%; 1%) total sperm count, 7% higher (95% CI: 0%; 14%) proportion of nonprogressive or immotile spermatozoa, 6% lower (95% CI: -11%; 0%) testes volume, 6% lower (95% CI: -12%; 1%) luteinizing hormone, 6% lower (95% CI: -12%; 1%) sex hormone-binding globulin and 5% lower (95% CI: -9%; 0%) testosterone levels compared with sons whose mothers had age at menarche at the same time as peers. Our study did not suggest that earlier maternal age at menarche was strongly associated with semen quality, testes volume or reproductive hormones in sons. However, the spline analyses indicated a potential inverted U-shaped association for sperm concentration and testes volume, and levels of sex hormone-binding globulin and testosterone. We found no strong evidence of mediation by timing of the sons' own pubertal development.

LIMITATIONS, REASONS FOR CAUTION

There was a rather low participation rate in the Fetal Programming of Semen Quality Cohort and we tried to counter it by applying selection weights. Maternal age at menarche was recalled during pregnancy, which may introduce misclassification, most likely nondifferential. Inaccuracy of the sons' recalled pubertal development years after the event may result in underestimation of the possible mediating role of pubertal timing.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings may represent a degree of shared heritability of reproductive health or be a result of an underlying epigenetic profile or unknown shared environmental, cultural or dietary exposure, causing both altered age at menarche and impaired reproductive health outcomes in sons. However, the exact mechanism for the investigated association remains unknown.

STUDY FUNDING/COMPETING INTEREST(S)

This article is part of the ReproUnion collaborative study, cofinanced by the European Union, Intereg V ÖKS (20200407). The FEPOS project was further funded by the Lundbeck Foundation (R170-2014-855), the Capital Region of Denmark, Medical doctor Sofus Carl Emil Friis and spouse Olga Doris Friis's Grant, Axel Muusfeldt's Foundation (2016-491), A.P. Møller Foundation (16-37), the Health Foundation and Dagmar Marshall's Fond. Additionally, this study received funding from Aarhus University. There are no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

A. Sørensen T, Elhakeem A, Santos AC, Pinot de Moira A, Heude B, Iñiguez C, Pizzi C, Simons E, Voerman E, Corpeleijn E, Zariouh F, Santorelli G, Inskip HM, Barros H, Carson J, Harris JR, Nader JL, Ronkainen J, Strandberg-Larsen K, Santa-Marina L, Calas L, Cederkvist L, Popovic M, Charles MA, Welten M, Vrijheid M, Azad M, Subbarao P, Burton P, Mandhane PJ, Huang RC, Wilson RC, Haakma S, Fernández-Barrés S, Turvey S, Santos S, Tough SC, Sebert S, Moraes TJ, Salika T, Jaddoe VWV, Lawlor DA, Nybo Andersen AM. Gestational age at birth and body size from infancy through adolescence: An individual participant data meta-analysis on 253,810 singletons in 16 birth cohort studies

BACKGROUND

Preterm birth is the leading cause of perinatal morbidity and mortality and is associated with adverse developmental and long-term health outcomes, including several cardiometabolic risk factors and outcomes. However, evidence about the association of preterm birth with later body size derives mainly from studies using birth weight as a proxy of prematurity rather than an actual length of gestation. We investigated the association of gestational age (GA) at birth with body size from infancy through adolescence.

METHODS AND FINDINGS

We conducted a two-stage individual participant data (IPD) meta-analysis using data from 253,810 mother-child dyads from 16 general population-based cohort studies in Europe (Denmark, Finland, France, Italy, Norway, Portugal, Spain, the Netherlands, United Kingdom), North America (Canada), and Australasia (Australia) to estimate the association of GA with body mass index (BMI) and overweight (including obesity) adjusted for the following maternal characteristics as potential confounders: education, height, prepregnancy BMI, ethnic background, parity, smoking during pregnancy, age at child's birth, gestational diabetes and hypertension, and preeclampsia. Pregnancy and birth cohort studies from the LifeCycle and the EUCAN-Connect projects were invited and were eligible for inclusion if they had information on GA and minimum one measurement of BMI between infancy and adolescence. Using a federated analytical tool (DataSHIELD), we fitted linear and logistic regression models in each cohort separately with a complete-case approach and combined the regression estimates and standard errors through random-effects study-level meta-analysis providing an overall effect estimate at early infancy (>0.0 to 0.5 years), late infancy (>0.5 to 2.0 years), early childhood (>2.0 to 5.0 years), mid-childhood (>5.0 to 9.0 years), late childhood (>9.0 to 14.0 years), and adolescence (>14.0 to 19.0 years). GA was positively associated with BMI in the first decade of life, with the greatest increase in mean BMI z-score during early infancy (0.02, 95% confidence interval (CI): 0.00; 0.05, p < 0.05) per week of increase in GA, while in adolescence, preterm individuals reached similar levels of BMI (0.00, 95% CI: -0.01; 0.01, p 0.9) as term counterparts. The association between GA and overweight revealed a similar pattern of association with an increase in odds ratio (OR) of overweight from late infancy through mid-childhood (OR 1.01 to 1.02) per week increase in GA. By adolescence, however, GA was slightly negatively associated with the risk of overweight (OR 0.98 [95% CI: 0.97; 1.00], p 0.1) per week of increase in GA. Although based on only four cohorts (n = 32,089) that reached the age of adolescence, data suggest that individuals born very preterm may be at increased odds of overweight (OR 1.46 [95% CI: 1.03; 2.08], p < 0.05) compared with term counterparts. Findings were consistent across cohorts and sensitivity analyses despite considerable heterogeneity in cohort characteristics. However, residual confounding may be a limitation in this study, while findings may be less generalisable to settings in low- and middle-income countries.

CONCLUSIONS

This study based on data from infancy through adolescence from 16 cohort studies found that GA may be important for body size in infancy, but the strength of association attenuates consistently with age. By adolescence, preterm individuals have on average a similar mean BMI to peers born at term.

Maternal stress during pregnancy and gestational duration: A cohort study from the Danish National Birth Cohort

BACKGROUND

Preterm birth is one of the most important contributors to neonatal mortality and morbidity. Experiencing stress during pregnancy may increase the risk of adverse birth outcomes, including preterm birth. This association has been observed in previous studies, but differences in measures used limit comparability.

OBJECTIVE

The objective of the study was to investigate the association between two measures of maternal stress during pregnancy, life stress and emotional distress, and gestation duration.

METHODS

Women recruited in the Danish National Birth Cohort from 1996 to 2002, who provided information on their stress level during pregnancy and expecting a singleton baby, were included in the study. We assessed the associations between the level of life stress and emotional distress in quartiles, both collected at 31 weeks of pregnancy on average, and the rate of giving birth using Cox regression within intervals of the gestational period.

RESULTS

A total of 80,991 pregnancies were included. Women reporting moderate or high levels of life stress vs no stress had a higher rate of giving birth earlier within all intervals of gestational age (e.g. high level: 27-33 weeks: hazard ratio (HR) 1.38, 95% confidence interval (CI) 1.04, 1.84; 34-36 weeks: 1.10, 95% CI 0.97, 1.25; 37-38 weeks: 1.21, 95% CI 1.15, 1.28). These associations between life stress and preterm birth were mainly driven by pregnancy worries. For emotional distress, a high level of distress was associated with shorter length of gestation in the preterm (27-33 weeks: 1.38, 95% CI 1.02, 1.86; 34-36 weeks: 1.05, 95% CI 0.91, 1.19) and early term (1.11, 95% CI 1.04, 1.17) intervals.

CONCLUSIONS

Emotional distress and life stress were shown to be associated with gestational age at birth, with pregnancy-related stress being the single stressor driving the association. This suggests that reverse causality may, at least in parts, explain the earlier findings of stress as a risk factor for preterm birth.

Prenatal nitrate exposure from diet and drinking water and timing of puberty in sons and daughters: A nationwide cohort study

BACKGROUND

In Western countries, age at pubertal development has declined during the last century in girls, and probably also in boys. No studies have investigated whether nitrate, a widespread environmental exposure with teratogenic and hormone disrupting properties, might affect timing of puberty.

OBJECTIVES

We investigated if prenatal exposure to nitrate from drinking water and diet was associated with timing of puberty.

METHODS

This cohort study included 15,819 children born from 2000 to 2003 within the Danish National Birth Cohort. Self-reported information on current status of various pubertal milestones was provided every six months by a questionnaire from 11 years of age until 18 years or full maturity, whichever came first. Maternal nitrate intake from diet (mg/day) was derived from a mid-pregnancy food frequency questionnaire and individual level nitrate exposure from drinking water (mg/L) was derived using measurements from Danish public waterworks. Adjusted average differences in months in age at attaining several pubertal milestones as well as the average age difference in age at attaining all the milestones were estimated separately for diet and water using a regression model for interval-censored data. C- and E-vitamin, red meat and processed meat intake were explored as potential effect modifiers in sub-analyses.

RESULTS

No strong associations were observed between prenatal exposure to nitrate and timing of puberty in children. However, sons born of mothers with a nitrate concentration in drinking water at their residential address of > 25 mg/L (half of the World Health Organisation (WHO) guideline value) compared with ≤ 1 mg/L showed a tendency towards earlier age at pubertal development with an average age difference of -1.2 months (95 % confidence interval,-3.0;0.6) for all the pubertal milestones combined.

DISCUSSION

Studies including more highly exposed children are needed before the current WHO drinking water guideline value for nitrate can be considered safe concerning pubertal development.

Exposure to natural environments during pregnancy and birth outcomes in 11 European birth cohorts

Research suggests that maternal exposure to natural environments (i.e., green and blue spaces) promotes healthy fetal growth. However, the available evidence is heterogeneous across regions, with very few studies on the effects of blue spaces. This study evaluated associations between maternal exposure to natural environments and birth outcomes in 11 birth cohorts across nine European countries. This study, part of the LifeCycle project, was based on a total sample size of 69,683 newborns with harmonised data. For each participant, we calculated seven indicators of residential exposure to natural environments: surrounding greenspace in 100m, 300m, and 500m using Normalised Difference Vegetation Index (NDVI) buffers, distance to the nearest green space, accessibility to green space, distance to the nearest blue space, and accessibility to blue space. Measures of birth weight and small for gestational age (SGA) were extracted from hospital records. We used pooled linear and logistic regression models to estimate associations between exposure to the natural environment and birth outcomes, controlling for the relevant covariates. We evaluated the potential effect modification by socioeconomic status (SES) and region of Europe and the influence of ambient air pollution on the associations. In the pooled analyses, residential surrounding greenspace in 100m, 300m, and 500m buffer was associated with increased birth weight and lower odds for SGA. Higher residential distance to green space was associated with lower birth weight and higher odds for SGA. We observed close to null associations for accessibility to green space and exposure to blue space. We found stronger estimated magnitudes for those participants with lower educational levels, from more deprived areas, and living in the northern European region. Our associations did not change notably after adjustment for air pollution. These findings may support implementing policies to promote natural environments in our cities, starting in more deprived areas.

Nitrate in Maternal Drinking Water during Pregnancy and Measures of Male Fecundity in Adult Sons

Animal studies indicate deleterious effects of nitrate exposure on fecundity, but effects in humans are unknown, both for the prenatal and postnatal periods. We aimed to investigate if exposure to nitrate in maternal drinking water during the sensitive period of fetal life is associated with measures of fecundity in the adult sons. In a sub-analysis, the potential effects of nitrate exposure in adulthood were investigated. This cohort included 985 young adult men enrolled in The Fetal Programming of Semen Quality Cohort (FEPOS). Semen characteristics, testes volume and reproductive hormones were analyzed in relation to nitrate concentration in maternal drinking water, using a negative binomial regression model. The nitrate concentration in drinking water was obtained from monitoring data from Danish waterworks that were linked with the mothers' residential address during pregnancy. The median nitrate concentration in maternal drinking water was 2 mg/L. At these low exposure levels, which are far below the World Health Organization's (WHO) guideline value of 50 mg/L, we did not find indications of harmful effects of nitrate on the investigated measures of male fecundity.

SART CORS IVF registry: looking to the past to shape future perspectives

PURPOSE

The SART CORS database is an informative source of IVF clinic-specific linked data that provides cumulative live birth rates from medically assisted reproduction in the United States (US). These data are used to develop best practice guidelines, for research, quality assurance, and post-market surveillance of assisted reproductive technologies. Here, we sought to investigate the key areas of current research focus (higher-order categories), discover gaps or underserved areas of ART research, and examine the potential application and impact of newer ART adjuvants, future data collection, and analysis needs.

METHODS

We conducted a systematic review (PRISMA guidelines) to quantify unique output metrics of the SART CORS database. Included were SART member reporting clinics: full-length publications from 2004 to 2021 and conference abstracts from 2015 to 2021, the two key timepoints when the SART CORS database underwent transformative shifts in data collection.

RESULTS

We found 206 abstracts presented from 2015 to 2021, 189 full-length peer-reviewed publications since 2004, with 654 unique authors listed on these publications. A total of 19 publications have been highly impactful, garnering over 100 citations at the time of writing. Several higher-order categories, such as endometriosis and tubal infertility, have few publications. The conversion of conference abstracts to full-length papers ranged from 15 to 35% from 2015 to 2021.

CONCLUSIONS

A substantial body of literature has been generated by analyzing the SART CORS database. Full-length publications have increased year over year. Some topic areas, such as endometriosis and tubal infertility, may be underrepresented. Conversion of conference abstracts to full-length publications has been low, indicating that more organizational support may be needed to ensure that research is methodologically sound and researchers supported to reach full publication status.

Gender incongruence and timing of puberty: a population-based cohort study

OBJECTIVE

To study whether the timing of puberty in adolescents who reported gender incongruence (incongruence between birth-assigned sex and self-identified gender) was different from those adolescents who reported gender congruence.

DESIGN

Population-based cohort study using data from the Danish National Birth Cohort.

SETTING

Not applicable.

PATIENT(S)

Birth-assigned boys and girls born between 2000 and 2003, who self-reported gender incongruence at 11 years (N = 10,046) and their pubertal developmental stages from age 11 years to every 6 months throughout puberty were included.

INTERVENTION(S)

Not applicable.

MAIN OUTCOME MEASURE

Mean age differences in months at reaching Tanner stages 2-5 for breast or genital development and pubic hair, voice break, first ejaculation, menarche, axillary hair, acne, and the average difference at attaining all pubertal milestones (primary outcome).

RESULT(S)

In total, 549 (5.5% ) adolescents reported part or full gender incongruence at 11 years. Tendencies toward earlier timing of puberty were observed in adolescents who reported part gender incongruence (average difference, birth-assigned boys: -3.2 months [95% confidence interval {CI}: -6.7; 0.3]; birth-assigned girls: -2.0 months [95% CI: -3.9; -0.1]). Tendencies toward earlier timing of puberty were observed in adolescents who reported full gender incongruence (average difference, birth-assigned boys: -2.4 months [95% CI: -5.0; 0.4]; birth-assigned girls: -1.9 months [95% CI: -5.1; 1.2]).

CONCLUSIONS

The results from this study indicated that birth-assigned boys and girls who reported either part or full gender incongruence tended to reach puberty slightly earlier than those adolescents who reported gender congruence at 11 years of age. Knowledge on the timing of puberty among adolescents who experience gender incongruence is essential to inform mutual decision-making in clinical settings.

Semen quality and reproductive hormones in sons of subfertile couples: a cohort study

OBJECTIVE

To study the associations between parental subfecundity, assessed by time to pregnancy and use of medically-assisted reproduction, and reproductive health of young men.

DESIGN

Cohort study.

SETTING

Denmark.

PATIENT(S)

A total of 1,058 men in the Fetal Programming of Semen quality cohort, a subcohort of the Danish National Birth Cohort.

INTERVENTION(S)

From 2017-2019, men were recruited and provided semen and blood samples. Information on parental time to pregnancy and use of medically-assisted reproduction (including type of treatment) as well as demographic, health, and lifestyle factors were available. We estimated the crude and adjusted relative percentage differences with 95% confidence intervals (CIs) in the outcomes according to time to pregnancy and use of medically-assisted reproduction, using multiple adjusted negative binomial regression analysis.

MAIN OUTCOME MEASURE(S)

Semen characteristics (semen volume, sperm concentration, total sperm count, sperm motility, and morphology), testicular volume, and reproductive hormone levels (follicle stimulating hormone, luteinizing hormone, testosterone, estradiol, sex hormone-binding globulin, and free androgen index).

RESULT(S)

Overall, semen quality and levels of reproductive hormones were not lower among sons of subfecund parents reporting a time to pregnancy >6 months or use of intrauterine insemination. Sons conceived after in vitro fertilization or intracytoplasmic sperm injection, had a higher semen concentration (29%; 95% CI, -7%-79%) and a higher percentage of sperm with normal morphology (20%; 95% CI, -8%-56%), but with 95% CI overlapping the null. Moreover, these sons had slightly higher estradiol levels (30%; 95% CI, 7%-57%). The absolute differences seen were small, and the clinical significance of these differences are unknown.

CONCLUSION(S)

We found no major difference in semen quality or reproductive hormones in sons conceived by subfertile couples or with the use of medically-assisted reproduction.

Maternal Exposure to Per- and Polyfluoroalkyl Substances (PFAS) and Male Reproductive Function in Young Adulthood: Combined Exposure to Seven PFAS

BACKGROUND

Concerns remain about the human reproductive toxicity of the widespread per- and polyfluoroalkyl substances (PFAS) during early stages of development.

OBJECTIVES

We examined associations between maternal plasma PFAS levels during early pregnancy and male offspring reproductive function in adulthood.

METHODS

The study included 864 young men (age range:18.9-21.2 y) from the Fetal Programming of Semen Quality (FEPOS) cohort established between 2017 and 2019. Plasma samples from their mothers, primarily from the first trimester, were retrieved from the Danish National Biobank and levels of 15 PFAS were measured. Seven PFAS had detectable levels above the limit of detection in >80% of the samples and were included in analyses. Semen quality, testicular volume, and levels of reproductive hormones and PFAS were assessed in the young men. We used weighted quantile sum (WQS) regression to estimate the associations between combined exposure to maternal PFAS and reproductive function, and negative binomial regression to estimate the associations of single substances, while adjusting for a range of a priori-defined fetal and postnatal risk factors.

RESULTS

By a 1-unit increase in the WQS index, combined maternal PFAS exposure was associated with lower sperm concentration (-8%; 95% CI: -16%, -1%), total sperm count (-10%; 95% CI: -17%, -2%), and a higher proportion of nonprogressive and immotile sperm (5%; 95% CI: 1%, 8%) in the young men. Different PFAS contributed to the associations with varying strengths; however, perfluoroheptanoic acid was identified as the main contributor in the analyses of all three outcomes despite the low concentration. We saw no clear association between exposure to maternal PFAS and testicular volume or reproductive hormones.

DISCUSSION

In a sample of young men from the general Danish population, we observed consistent inverse associations between exposure to maternal PFAS and semen quality. The study needs to be replicated in other populations, taking combined exposure, as well as emerging short-chain PFAS, into consideration. https://doi.org/10.1289/EHP10285.

Drinking water nitrate and risk of pregnancy loss: a nationwide cohort study

BACKGROUND

Nitrate contamination is seen in drinking water worldwide. Nitrate may pass the placental barrier. Despite suggestive evidence of fetal harm, the potential association between nitrate exposure from drinking water and pregnancy loss remains to be studied. We aimed to investigate if nitrate in drinking water was associated with the risk of pregnancy loss.

METHODS

We conducted a nationwide cohort study of 100,410 pregnancies (enrolled around gestational week 11) in the Danish National Birth Cohort (DNBC) during 1996-2002. Spontaneous pregnancy losses before gestational week 22 were ascertained from the Danish National Patient Registry and DNBC pregnancy interviews. Using the national drinking water quality-monitoring database Jupiter, we estimated the individual and time-specific nitrate exposure by linking geocoded maternal residential addresses with water supply areas. The nitrate exposure was analyzed in spline models using a log-transformed continuous level or classified into five categories. We used Cox proportional hazards models to estimate associations between nitrate and pregnancy loss and used gestational age (days) as the time scale, adjusting for demographic, health, and lifestyle variables.

RESULTS

No consistent associations were found when investigating the exposure as a categorical variable and null findings were also found in trimester specific analyses. In the spline model using the continuous exposure variable, a modestly increased hazard of pregnancy loss was observed for the first trimester at nitrate exposures between 1 and 10 mg/L, with the highest. adjusted hazard ratio at 5 mg/L of nitrate of 1.16 (95% CI: 1.01, 1.34). This trend was attenuated in the higher exposure ranges.

CONCLUSION

No association was seen between drinking water nitrate and the risk of pregnancy loss when investigating the exposure as a categorical variable. When we modelled the exposure as a continuous variable, a dose-dependent association was found between drinking water nitrate exposure in the first trimester and the risk of pregnancy loss. Very early pregnancy losses were not considered in this study, and whether survival bias influenced the results should be further explored.

Maternal polycystic ovarian syndrome and pubertal development in daughters and sons: a population-based cohort study

STUDY QUESTION

Does maternal polycystic ovarian syndrome (PCOS) affect the timing of pubertal development in daughters and sons?

SUMMARY ANSWER

Maternal PCOS was associated with earlier adrenarche in daughters.

WHAT IS KNOWN ALREADY

Female adolescents with PCOS often experience earlier adrenarche compared to adolescents without PCOS, due to hyperandrogenism. Likewise, they usually have hyperandrogenism during pregnancy, which might potentially affect the development of the foetus, including its future reproductive health.

STUDY DESIGN, SIZE, DURATION

In this population-based cohort study, we included 15 596 mothers-child pairs from the Danish National Birth Cohort (DNBC) Puberty Cohort, who were followed from foetal life until full sexual maturation or 18 years of age.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Using register-based and self-reported information on maternal PCOS and menstrual irregularities, collected during pregnancy, we categorized the mothers as having PCOS (n = 251), oligomenorhoea (n = 134), 'other menstrual irregularities' (n = 2411) or no menstrual abnormalities (reference group, n = 12 800). The children provided self-reported information on pubertal development every 6 months from the age of 11 years. The main outcome measures were adjusted mean age differences (in months) at attaining several individual pubertal milestones using an interval-censored regression model, as well as the average difference in age at attaining all pubertal milestones combined into a single estimate using Huber-White robust variance estimation.

MAIN RESULTS AND THE ROLE OF CHANCE

We found that maternal PCOS was associated with an accelerated pubertal development in daughters with an overall average difference of -3.3 (95% CI: -6.3; -0.4) months based on all pubertal milestones compared to the reference group. When further looking into the average difference for adrenarche only (pubarche, axillary hair and acne), the average difference was -5.4 (95% CI: -8.7; -2.1) months compared to the reference group; whereas thelarche and menarche did not occur earlier in daughters of mothers with PCOS (average difference: -0.8 (95% CI: -3.9; 2.4) months). Oligomenorrhoea and 'other menstrual irregularities' were not associated with pubertal development in daughters. Neither PCOS, oligomenorrhoea nor 'other menstrual irregularities' were associated with pubertal development in sons.

LIMITATIONS, REASONS FOR CAUTION

We expect some degree of non-differential misclassification of maternal PCOS and menstrual irregularities as well as pubertal development in the children.

WIDER IMPLICATIONS OF THE FINDINGS

Maternal PCOS might accelerate adrenarche in daughters. Whether this is due to genetics, epigenetics or prenatal programming by hyperandrogenism in foetal life remains unsolved. The results from the present study can be generalized to Caucasian populations.

STUDY FUNDING/COMPETING INTEREST(S)

The study is funded by the Faculty of Health at Aarhus University. The authors have no financial relationships or competing interests to disclose.

TRIAL REGISTRATION NUMBER

N/A.

In utero exposure to perfluoroalkyl and polyfluoroalkyl substances and attention and executive function in the offspring: A study in the Danish National Birth Cohort

BACKGROUND

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are ubiquitous in the environment and accumulate in humans. PFAS are suspected to affect the neuropsychological function of children, but only few studies have evaluated the association with childhood attention and executive function.

OBJECTIVES

To investigate the association between intrauterine exposure to PFAS and offspring attention and executive function.

METHODS

A total of 1593 children from the Danish National Birth Cohort, born 1996-2003, were included. The levels of 16 PFAS were measured in maternal plasma during pregnancy. At 5 years of age, the Test of Everyday Attention for Children at Five (TEACh-5) and the Behavior Rating Inventory of Executive Function (BRIEF) were performed. TEACh-5 scores were standardized to a mean of 0 and standard deviation (SD) of 1. BRIEF scores were standardized to a mean of 50 and a SD of 10. The associations between levels of seven PFAS and TEACh-5 and BRIEF were examined by multivariable linear regression adjusted for potential confounders.

RESULTS

Perfluorooctane sulfonamide (PFOSA) was associated with poorer selective attention [standardized mean difference (95% confidence interval) -0.5 (-0.7, -0.3), highest versus lowest quartile]. Other PFAS were not clearly associated with selective attention, and we found no clear associations between PFAS exposure and sustained attention. For parent rated executive function, perfluorooctanoate (PFOA) was associated with poorer scores, standardized mean difference 3.8 (95% confidence interval 1.6, 6.0), highest versus lowest quartile. Regarding other PFAS, the associations were less clear. We found no clear associations between any PFAS and executive function rated by preschool teachers.

CONCLUSION

Intrauterine exposure to PFOSA was associated with poorer selective attention, while PFOA was associated with poorer executive function. Given the widespread nature of PFAS exposure, these findings may have public health implications, warranting further investigation.

Per- and polyfluoroalkyl substances (PFAS) and male reproductive function in young adulthood; a cross-sectional study

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are a large family of persistent industrial chemicals with endocrine disrupting properties.

OBJECTIVES

To examine biomarkers of reproductive function in young adult males according to current environmental exposure to single and combined PFAS.

METHODS

The study population consisted of young men (n = 1041, age 18-21) from the Fetal Programming of Semen Quality (FEPOS) cohort. These men were recruited from pregnancies included in the Danish National Birth Cohort (DNBC) between 1996 and 2002. From 2017 to 2019, participants answered an online questionnaire, completed a clinical examination and provided a blood and a semen sample. Exposure to 15 PFAS was measured in plasma. Six compounds were quantified above the limit of detection in at least 80% of the participants. We applied negative binomial regression and weighted quantile sum (WQS) regression models to assess associations between single and combined exposure to PFAS and measures of semen quality, testicular volume and reproductive hormones among the young men.

RESULTS

We found no consistent associations between plasma concentrations of PFAS, semen quality and testicular volume. Higher levels of single and combined PFAS were associated with slightly higher levels of follicle-stimulating hormone (FSH) (WQS 4% difference, 95% confidence interval: 0, 9). Perfluorooctanoic acid (PFOA) was the main contributor to this finding with positive signals also from perfluorodecanoic acid (PFDA) and perfluorohexane sulfonic acid (PFHxS).

DISCUSSION

We examined exposure to a range of common PFAS in relation to biomarkers of male reproductive function and found an association with higher levels of FSH among young men from the general population in Denmark. Further studies on especially combined exposure to PFAS are needed to expand our understanding of potential endocrine disruption from both legacy and emerging compounds in relation to male reproductive function.

Breastfeeding, pregnancy, medicines, neurodevelopment, and population databases: the information desert

BACKGROUND

The pharmacoepidemiology of the long-term benefits and harms of medicines in pregnancy and breastfeeding has received little attention. The impact of maternal medicines on children is increasingly recognised as a source of avoidable harm. The focus of attention has expanded from congenital anomalies to include less visible, but equally important, outcomes, including cognition, neurodevelopmental disorders, educational performance, and childhood ill-health. Breastfeeding, whether as a source of medicine exposure, a mitigator of adverse effects or as an outcome, has been all but ignored in pharmacoepidemiology and pharmacovigilance: a significant 'blind spot'.

WHOLE-POPULATION DATA ON BREASTFEEDING

WHY WE NEED THEM: Optimal child development and maternal health necessitate breastfeeding, yet little information exists to guide families regarding the safety of medicine use during lactation. Breastfeeding initiation or success may be altered by medicine use, and breastfeeding may obscure the true relationship between medicine exposure during pregnancy and developmental outcomes. Absent or poorly standardised recording of breastfeeding in most population databases hampers analysis and understanding of the complex relationships between medicine, pregnancy, breastfeeding and infant and maternal health. The purpose of this paper is to present the arguments for breastfeeding to be included alongside medicine use and neurodevelopmental outcomes in whole-population database investigations of the harms and benefits of medicines during pregnancy, the puerperium and postnatal period. We review: 1) the current situation, 2) how these complexities might be accommodated in pharmacoepidemiological models, using antidepressants and antiepileptics as examples; 3) the challenges in obtaining comprehensive data.

CONCLUSIONS

The scarcity of whole-population data and the complexities of the inter-relationships between breastfeeding, medicines, co-exposures and infant outcomes are significant barriers to full characterisation of the benefits and harms of medicines during pregnancy and breastfeeding. This makes it difficult to answer the questions: 'is it safe to breastfeed whilst taking this medicine', and 'will this medicine interfere with breastfeeding and/ or infants' development'?

Perinatal mental health: how nordic data sources have contributed to existing evidence and future avenues to explore

PURPOSE

Perinatal mental health disorders affect a significant number of women with debilitating and potentially life-threatening consequences. Researchers in Nordic countries have access to high quality, population-based data sources and the possibility to link data, and are thus uniquely positioned to fill current evidence gaps. We aimed to review how Nordic studies have contributed to existing evidence on perinatal mental health.

METHODS

We summarized examples of published evidence on perinatal mental health derived from large population-based longitudinal and register-based data from Denmark, Finland, Iceland, Norway and Sweden.

RESULTS

Nordic datasets, such as the Danish National Birth Cohort, the FinnBrain Birth Cohort Study, the Icelandic SAGA cohort, the Norwegian MoBa and ABC studies, as well as the Swedish BASIC and Mom2B studies facilitate the study of prevalence of perinatal mental disorders, and further provide opportunity to prospectively test etiological hypotheses, yielding comprehensive suggestions about the underlying causal mechanisms. The large sample size, extensive follow-up, multiple measurement points, large geographic coverage, biological sampling and the possibility to link data to national registries renders them unique. The use of novel approaches, such as the digital phenotyping data in the novel application-based Mom2B cohort recording even voice qualities and digital phenotyping, or the Danish study design paralleling a natural experiment are considered strengths of such research.

CONCLUSIONS

Nordic data sources have contributed substantially to the existing evidence, and can guide future work focused on the study of background, genetic and environmental factors to ultimately define vulnerable groups at risk for psychiatric disorders following childbirth.

Gene-environment interactions related to maternal exposure to environmental and lifestyle-related chemicals during pregnancy and the resulting adverse fetal growth: a review

Background

There are only limited numbers of reviews on the association of maternal-child genetic polymorphisms and environmental and lifestyle-related chemical exposure during pregnancy with adverse fetal growth. Thus, this article aims to review: (1) the effect of associations between the above highlighted factors on adverse fetal growth and (2) recent birth cohort studies regarding environmental health risks.

Methods

Based on a search of the PubMed database through August 2021, 68 epidemiological studies on gene-environment interactions, focusing on the association between environmental and lifestyle-related chemical exposure and adverse fetal growth was identified. Moreover, we also reviewed recent worldwide birth cohort studies regarding environmental health risks.

Results

Thirty studies examined gene-smoking associations with adverse fetal growth. Sixteen maternal genes significantly modified the association between maternal smoking and adverse fetal growth. Two genes significantly related with this association were detected in infants. Moreover, the maternal genes that significantly interacted with maternal smoking during pregnancy were cytochrome P450 1A1 (CYP1A1), X-ray repair cross-complementing protein 3 (XRCC3), interleukin 6 (IL6), interleukin 1 beta (IL1B), human leukocyte antigen (HLA) DQ alpha 1 (HLA-DQA1), HLA DQ beta 1 (HLA-DQB1), and nicotinic acetylcholine receptor. Fetal genes that had significant interactions with maternal smoking during pregnancy were glutathione S-transferase theta 1 (GSTT1) and fat mass and obesity-associated protein (FTO). Thirty-eight studies examined the association between chemical exposures and adverse fetal growth. In 62 of the 68 epidemiological studies (91.2%), a significant association was found with adverse fetal growth. Across the studies, there was a wide variation in the analytical methods used, especially with respect to the genetic polymorphisms of interest, environmental and lifestyle-related chemicals examined, and the study design used to estimate the gene-environment interactions. It was also found that a consistently increasing number of European and worldwide large-scale birth cohort studies on environmental health risks have been conducted since approximately 1996.

Conclusion

There is some evidence to suggest the importance of gene-environment interactions on adverse fetal growth. The current knowledge on gene-environment interactions will help guide future studies on the combined effects of maternal-child genetic polymorphisms and exposure to environmental and lifestyle-related chemicals during pregnancy.

Supplementary information

The online version contains supplementary material available at https://doi.org/10.1265/ehpm.21-00033.

The continuing evolution of birth cohort studies: achievements and challenges

Well-designed birth cohorts are able to estimate prevalence/distribution of various health events/outcomes, and to link early-life origins with adult health and function. The past two decades have seen a surge in the establishment of new birth cohorts and their accompanying research. We discussed distinct designs of current birth cohort studies, reviewed their achievements, and highlighted insights obtained from birth cohort studies, as well as challenges we are facing. Birth cohort studies are providing increasing opportunities to identify determining factors for short- and long-term health, yielding substantial evidence to uncover biological mechanisms of diseases and phenotypes, and providing further insights for public health. Dynamic monitoring, accurate measurements, long-term follow-ups and collaborative efforts are warranted in new birth cohorts to elucidate the nature of life course relationships in contemporary generation.

Maternal thyroid disease in pregnancy and timing of pubertal development in sons and daughters

OBJECTIVE

To study whether maternal thyroid disease in pregnancy is associated with pubertal timing in sons and daughters.

DESIGN

Cohort study.

SETTING

National birth cohort and health registers.

PATIENT(S)

A total of 15,763 mothers and children from the Danish National Birth Cohort and its Puberty Cohort.

INTERVENTION(S)

Register-based and self-reported information on maternal thyroid diseases during pregnancy (hyperthyroidism, hypothyroidism, benign goiter, or no thyroid disease [reference group]).

MAIN OUTCOME MEASURE(S)

The adjusted mean age difference (months) at attaining several self-reported pubertal milestones collected every 6 months using an interval-censored regression and the average difference in age at attaining all pubertal milestones using the Huber-White robust variance estimation (primary outcome).

RESULT(S)

Sons of mothers with hyperthyroidism had earlier pubertal development (average difference, -2.9 [95% confidence interval (CI), -5.0 to -0.7] months) than unexposed sons. Maternal hypothyroidism was not associated with pubertal development in sons (average difference, -1.2 [95% CI, -5.1 to 2.7] months). We observed nonstatistically significant indications of earlier pubertal development in sons of mothers with benign goiter (average difference, -1.9 [95% CI, -4.6 to 0.9] months). Maternal thyroid disease was not associated with pubertal development in daughters (average difference (months), hyperthyroidism, -0.8 [95% CI, -2.8 to 1.2]; hypothyroidism, 0.3 [95% CI, -3.1 to 3.8]; and benign goiter, 0.7 [95% CI, -2.0 to 3.4]).

CONCLUSION(S)

We found indications of earlier pubertal development in sons of mothers with hyperthyroidism. More research is needed to further investigate the observed sex-specific association.

Multiple health complaints in preadolescence and hospital contacts during adolescence: a prospective cohort study

Multiple health complaints (MHC) is increasing among preadolescents in many countries, but their prognostic effect for individual thriving or societal resource use is scarcely studied. This makes interpreting the significance of this increase challenging. We contribute by examining whether MHC in preadolescence predicts hospital contacts in adolescence by doing a nation-wide population-based cohort-study following preadolescents from the Danish National Birth-Cohort from 2010 to 2018. 96,382 children were invited at age 11. Responses to a modified version of the Health Behaviour in School Children Symptom Checklist (headache, dizziness, stomachache, irritability, feeling nervous, difficulty in getting to sleep and feeling low) was dichotomized into MHC (≥ 2 concurrent symptoms, each with a frequency of at least weekly, yes/no). Hospital contacts were derived from Danish registers from the date of answering the questionnaire to December 31st 2018. Negative binomial regression estimated incidence rate ratios (IRRs) comparing children with MHC to children without. Analyses were further broken down by hospital sector (psychiatric/somatic) and contact type (in-patient/out-patient/emergency room). 47,365 (49.1%) responded. Mean age was 11.2 years, 52% girls. 10.3% of responders reported MHC. For hospital contacts, the unadjusted IRR was 1.74 [95% CI 1.65, 1.83]. Results were robust to adjustment for sociodemographic variables and somatic/psychiatric morbidity diagnosed before baseline, IRR 1.62 [95% CI 1.54-1.71]. In conclusion, MHC in preadolescents are prognostic of hospital contacts. This shows that we cannot ignore MHC, and to prevent potentially unhelpful healthcare use, we must act. Future research should focus on the underlying causes of MHC to understand which changes will be most helpful and thus how to act.

The effect of gluten in adolescents and young adults with gastrointestinal symptoms: a blinded randomised cross-over trial

BACKGROUND

The popularity of the gluten-free diet and sales of gluten-free products have increased immensely.

AIMS

To investigate whether gluten induces gastrointestinal symptoms, measured by self-reported questionnaires, as well as mental health symptoms in adolescents from a population-based cohort.

METHODS

The eligible participants (n = 273) were recruited from a population-based cohort of 1266 adolescents and had at least four different gastrointestinal symptoms. Phase one (n = 54) was a run-in phase where the participants lived gluten-free for 2 weeks. If they improved they continued to phase 2 (n = 33), a blinded randomised cross-over trial. Participants were blindly randomised either to start with 7 days of gluten, eating two granola bars containing 10 g of gluten or to 7 days on placebo, eating two granola bars without gluten, followed by the reverse and separated by a 7-day washout period. The effects of the intervention on gastrointestinal symptoms and mental health symptoms were assessed.

RESULTS

In total, 54/273 participants entered the run-in phase and 35 were eligible for randomization. A total of 33 were randomised and 32 completed the trial. The median age was 20.3 (IQR 19.2-20.9) and 32/33 participants were females. Compared with a placebo, gluten did not induce gastrointestinal symptoms. The difference in the average VAS was -0.01 (95% confidence interval -2.07 to 2.05). Nor did we find a difference in the outcomes measuring mental health.

CONCLUSION

Compared with placebo, adding gluten to the diet did not induce gastrointestinal symptoms or worsened mental health in adolescents recruited from a population-based cohort. The trial registration number is NCT04639921.

The impact of the initial and second national COVID-19 lockdowns on mental health in young people with and without pre-existing depressive symptoms

BACKGROUND

The evidence on mental health during COVID-19 evolved fast, but still little is known about the long-lasting impact of the sequential lockdowns. We examine changes in young people's mental health from before to during the initial and second more prolonged lockdown, and whether women and those with pre-existing depressive symptoms were disproportionally impacted.

METHODS

Participants reported on mental health indicators in an ongoing 18-year data collection in the Danish National Birth Cohort and in a COVID-19 survey, including 8 data points: 7 in the initial lockdown, and 1 year post. Changes in quality of life (QoL), mental well-being, and loneliness were estimated with random effect linear regressions on longitudinal data (N = 32,985), and linear regressions on repeated cross-sections (N = 28,579).

FINDINGS

Interim deterioration in mental well-being and loneliness was observed during the initial lockdown, and only in those without pre-existing depressive symptoms. During the second lockdown, a modest deterioration was again observed for mental well-being and loneliness. QoL likewise only declined among those without pre-existing symptoms, where women showed a greater decline than men. QoL did not normalise during the initial lockdown and remained at lower levels during the second lockdown. These findings were not replicated in the repeated cross-sections.

INTERPRETATION

Except for an interim decrease in mental health, and only in those without pre-existing depressive symptoms, this study's findings do not suggest a substantial detrimental impact of the lockdowns.

Predicting perinatal health outcomes using smartphone-based digital phenotyping and machine learning in a prospective Swedish cohort (Mom2B): study protocol

INTRODUCTION

Perinatal complications, such as perinatal depression and preterm birth, are major causes of morbidity and mortality for the mother and the child. Prediction of high risk can allow for early delivery of existing interventions for prevention. This ongoing study aims to use digital phenotyping data from the Mom2B smartphone application to develop models to predict women at high risk for mental and somatic complications.

METHODS AND ANALYSIS

All Swedish-speaking women over 18 years, who are either pregnant or within 3 months postpartum are eligible to participate by downloading the Mom2B smartphone app. We aim to recruit at least 5000 participants with completed outcome measures. Throughout the pregnancy and within the first year postpartum, both active and passive data are collected via the app in an effort to establish a participant's digital phenotype. Active data collection consists of surveys related to participant background information, mental and physical health, lifestyle, and social circumstances, as well as voice recordings. Participants' general smartphone activity, geographical movement patterns, social media activity and cognitive patterns can be estimated through passive data collection from smartphone sensors and activity logs. The outcomes will be measured using surveys, such as the Edinburgh Postnatal Depression Scale, and through linkage to national registers, from where information on registered clinical diagnoses and received care, including prescribed medication, can be obtained. Advanced machine learning and deep learning techniques will be applied to these multimodal data in order to develop accurate algorithms for the prediction of perinatal depression and preterm birth. In this way, earlier intervention may be possible.

ETHICS AND DISSEMINATION

Ethical approval has been obtained from the Swedish Ethical Review Authority (dnr: 2019/01170, with amendments), and the project fully fulfils the General Data Protection Regulation (GDPR) requirements. All participants provide consent to participate and can withdraw their participation at any time. Results from this project will be disseminated in international peer-reviewed journals and presented in relevant conferences.

Fetal exposure to maternal cigarette smoking and male reproductive function in young adulthood

Maternal smoking during pregnancy constitutes a potential, major risk factor for adult male reproductive function. In the hitherto largest longitudinal cohort, we examined biomarkers of reproductive function according to maternal smoking during the first trimester and investigated whether associations were mitigated by smoking cessation prior to the fetal masculinization programming window. Associations between exposure to maternal smoking and semen characteristics, testicular volume and reproductive hormones were assessed among 984 young men from the Fetal Programming of Semen Quality (FEPOS) cohort. Maternal smoking was assessed through interview data and measured plasma cotinine levels during pregnancy. We applied negative binomial, logistic and linear regression models to estimate differences in outcomes according to levels of maternal smoking. Sons of light smokers (≤ 10 cigarettes/day) had a 19% (95% CI - 29%, - 6%) lower sperm concentration and a 24% (95% CI - 35%, - 11%) lower total sperm count than sons of non-smokers. These estimates were 38% (95% CI - 52%, - 22%) and 33% (95% CI - 51%, - 8%), respectively, for sons of heavy smokers (> 10 cigarettes/day). The latter group also had a 25% (95% CI 1%, 54%) higher follitropin level. Similarly, sons exposed to maternal cotinine levels of  > 10 ng/mL had lower sperm concentration and total sperm count. Smoking cessation prior to gestational week seven was not associated with a higher reproductive capacity. We observed substantial and consistent exposure-response associations, providing strong support for the hypothesis that maternal smoking impairs male reproductive function. This association persisted regardless of smoking cessation in early pregnancy.

Housing environment and mental health of Europeans during the COVID-19 pandemic: a cross-country comparison

Many studies have investigated the impact of the COVID-19 pandemic on mental health. Throughout the pandemic, time spent at home increased to a great extent due to restrictive measures. Here we set out to investigate the relationship between housing conditions and the mental health of populations across European countries. We analyzed survey data collected during spring 2020 from 69,136 individuals from four cohorts from Denmark, France, and the UK. The investigated housing conditions included household density, composition, and crowding, access to outdoor facilities, dwelling type, and urbanicity. The outcomes were loneliness, anxiety, and life satisfaction. Logistic regression models were used, and results were pooled using random-effects meta-analysis. In the meta-analysis, living alone was associated with higher levels of loneliness (OR = 3.08, 95% CI 1.87–5.07), and lower life satisfaction (OR = 1.27, 95% CI 1.05–0.55), compared to living with others. Not having access to an outdoor space and household crowding were suggestively associated with worse outcomes. Living in crowded households, living alone, or lacking access to outdoor facilities may be particularly important in contributing to poor mental health during a lockdown. Addressing the observed fundamental issues related to housing conditions within society will likely have positive effects in reducing social inequalities, as well as improving preparedness for future pandemics.

Nitrate in Drinking Water and Time to Pregnancy or Medically Assisted Reproduction in Women and Men: A Nationwide Cohort Study in the Danish National Birth Cohort

Purpose

No studies have investigated if drinking water nitrate affects human fecundity. Experimental studies point at detrimental effects on fetal development and on female and male reproduction. This cohort study aimed to explore if female and male preconception and long-term exposure to nitrate in drinking water was associated with fecundability measured as time to pregnancy (TTP) or use of medically assisted reproduction (MAR) treatment.

Methods

The study population consisted of pregnant women recruited in their first trimester in 1996–2002 to the Danish National Birth Cohort. Preconception drinking-water nitrate exposure was estimated for the pregnant women (89,109 pregnancies), and long-term drinking water nitrate exposure was estimated from adolescence to conception for the pregnant women (77,474 pregnancies) and their male partners (62,000 pregnancies) by linkage to the national drinking water quality-monitoring database Jupiter. Difference in risk of TTP >12 months or use of MAR treatment between five exposure categories and log-transformed continuous models of preconception and long-term nitrate in drinking water were estimated. Binominal regression models for risk ratios (RR) were adjusted for age, occupation, education, population density, and lifestyle factors.

Results

Nitrate in drinking water (median preconception exposure: 1.9 mg/L; median long-term exposure: 3.3 mg/L) was not associated with TTP >12 months or use of MAR treatment, neither in the categorical nor in the continuous models.

Conclusion

We found no association between preconception or long-term exposure to drinking water nitrate and fecundability.

Birth with synthetic oxytocin and the risk of being overweight or obese during childhood

BACKGROUND

Despite the importance of oxytocinergic signalling for satiety regulation and energy balance, the impact of exposure to synthetic oxytocin during childbirth on obesity during childhood remains unknown.

OBJECTIVES

To examine the association between oxytocin exposure during labour and the risk of being overweight or obese during childhood.

METHODS

Synthetic oxytocin exposure data of mothers from the Danish Medical Birth Registry were linked with self-reported anthropometric data of their children from the Danish National Birth Cohort (5 months-11 years of age). Multinomial logistic regression and latent class growth analyses were performed to determine the association between oxytocin exposure and obesity during childhood.

RESULTS

With the exception of the normal weight-to-overweight group between ages 5 and 12 months, none of the other analyses revealed a significant association between synthetic oxytocin use and the risk of being overweight until the age of 11 years. Furthermore, latent class growth analysis did not reveal an association between oxytocin exposure at birth and the risk of being overweight or obese during childhood.

CONCLUSIONS

Our analysis of a large cohort of children who varied in their synthetic oxytocin exposure status at childbirth did not reveal an association between oxytocin exposure and the risk of childhood overweight/obesity.

Timing of Pubertal Development in Boys and Girls With Congenital Heart Defects: A Nationwide Cohort Study

Background

Children with congenital heart defects (CHD) have an increased risk of developmental delay. It remains sparsely investigated if these patients also have a delayed pubertal development. In this nationwide cohort study, we evaluated if CHD was associated with timing of puberty using longitudinally collected data on pubertal milestones.

Methods and Results

We used data from the Danish nationwide Puberty Cohort. Information on CHD was obtained from the Danish National Patient Register. Information on pubertal development was obtained from 15 780 children through questionnaires answered half‐yearly from 11 years until 18 years or full maturity. Using a multivariable regression model for censored time‐to‐event data, mean difference in age at attaining each pubertal milestone was estimated, including a combined pubertal marker. Compared with children without CHD, analyses were performed for both CHD overall and subdivided into simple and complex CHD. In a subanalysis, analyses were repeated in children born at term. In total, 137 children (62 boys and 75 girls) had a CHD diagnosis. Overall, no difference in age at pubertal timing was observed for children with CHD compared with unaffected children. The average differences were small for both boys (1.6 [95% CI, −2.6 to 5.7] months) and girls (1.0 [95% CI, −2.5 to 4.4] months). The same differences were observed when subdividing into simple or complex CHD and when restricting to children born at term.

Conclusions

We found no association between CHD and pubertal timing. For the group of children with complex CHD, we were unable to exclude a later pubertal timing.

Mode of delivery and short-term maternal mental health: A follow-up study in the Danish National Birth Cohort

OBJECTIVE

To estimate associations between mode of delivery and maternal mental health 6 months postpartum.

METHODS

Follow-up of mothers in the Danish National Birth Cohort. Symptoms of anxiety, depression or stress were self-reported at gestational week 30 and 6 months postpartum. Mode of delivery was categorized as spontaneous vaginal birth, instrumental vaginal birth, planned cesarean section and emergency cesarean section. Multiple linear and logistic regression models were used to compute differences and odds ratios (ORs) with 95% confidence intervals (CIs) for associations between delivery mode and mental health indicators adjusted for mental health before and during pregnancy.

RESULTS

Among 54 474 mothers, mental health indicators improved from pregnancy to 6 months postpartum for all delivery modes. Improvement was smallest in mothers with emergency cesarean section. Thus, compared to women with a spontaneous vaginal birth, women with emergency cesarean section more frequently reported symptoms of anxiety (OR 1.11; 0.98-1.24), depression (OR 1.25; 1.09-1.43) and stress (OR 1.14; 1.01-1.29) 6 months postpartum, and women with planned cesarean section more frequently reported symptoms of anxiety (OR 1.15; 1.01-1.29).

CONCLUSION

Mental health improved from pregnancy to 6 months postpartum regardless of delivery mode. Mothers with emergency cesarean section experienced more symptoms of emotional distress 6 months postpartum.

The China birth cohort study (CBCS)

The China birth cohort study (CBCS) is a prospective longitudinal, mega-cohort study and the first national-based birth cohort study, aiming to establish a birth cohort covering representative geographical areas of the whole of China to investigate risk factors for birth defects and develop strategies for their reduction. Pregnant women who are of Chinese nationality, are 6–13⁺⁶ weeks of gestation, plan to attend the routine antenatal examination and deliver in the study site, and give their informed, written consent are eligible to participate in this study. All participants are followed-up through an in-person interview at 20–23⁺⁶ weeks and again at 28–33⁺⁶ weeks of gestation, and at delivery, respectively. CBCS has been divided into three phases from 20th November 2017 to 31st December 2021, and the first two phases have now been completed on 29th February 2020, enrolling 120 377 eligible pregnant women during this period. During the same period a total of 40 837 participants had been followed up to the end of pregnancy. Study recruitment will continue until December 2021 to achieve the target of 500 000 participants. Meanwhile, biological samples including peripheral blood, amniocytes, cord blood, placenta, or umbilical cord tissue have been collected from participants according to various conditions. The incidence of birth defects in this group is 2.5% and congenital heart disease is the most common type of birth defect seen so far. A website is in the advanced stages of planning, to allow seamless data transfer and facilitate collaboration with groups around the world.

Associations of early-life pet ownership with asthma and allergic sensitization: a meta-analysis of >77,000 children from the EU Child Cohort Network

BACKGROUND

Studies examining associations of early-life cat and dog ownership with childhood asthma have reported inconsistent results. Several factors could explain these inconsistencies, including type of pet, timing and degree of exposure.

OBJECTIVE

To study associations of early-life cat and dog ownership with school-age asthma, including the role of type (cat versus dog), timing (never, prenatal or early childhood) and degree (number) of ownership, and the role of allergic sensitisation.

METHODS

We used harmonised data from 77,434 mother-child dyads aged 5-11 years from nine birth cohorts in the EU Child Cohort Network. Associations were examined through the DataSHIELD platform using adjusted logistic regression models, fitted separately for each cohort and combined using random-effects meta-analysis.

RESULTS

Early-life cat and dog ownership ranged between 12-45% and 7-47% respectively, and prevalence of asthma between 2-20%. There was no overall association between either cat or dog ownership and asthma (OR: 0.97 (95% CI: 0.87-1.09) and 0.92 (0.85-1.01), respectively). Timing and degree of ownership did not strongly influence associations. Cat and dog ownership were also not associated with cat- and dog-specific allergic sensitisation (OR: 0.92 (0.75-1.13) and 0.93 (0.57-1.54), respectively). However, cat- and dog-specific allergic sensitisation were strongly associated with school-age asthma (OR: 6.69 (4.91-9.10) and 5.98 (3.14-11.36), respectively). There was also some indication of an interaction between ownership and sensitisation, suggesting that ownership may exacerbate the risks associated with pet-specific sensitisation, but offer some protection against asthma in the absence of sensitisation.

CONCLUSION

Our findings do not support early-life cat and dog ownership in themselves increasing the risk of school-age asthma, but suggest that ownership may potentially exacerbate the risks associated with cat- and dog-specific allergic sensitisation.

Impact of housing conditions on changes in youth's mental health following the initial national COVID-19 lockdown: a cohort study

We aimed to investigate if declines in youth’s mental health during lockdown were dependent on housing condition among 7445 youth (median age ~ 20 years) from the Danish National Birth Cohort (DNBC), with data collected at 18 years of age and again three weeks into the first national lockdown (April 2020). We examined associations between housing conditions (access to outdoor spaces, urbanicity, household density, and household composition) and changes in mental health (mental well-being, Quality of Life (QoL) and loneliness). We report results from multivariate linear and logistic regression models. Youth without access to outdoor spaces experienced greater declines in mental well-being (vs. garden; mean difference: − 0·75 (95% CI − 1·14, − 0·36)), and correspondingly greater odds of onset of low mental well-being (vs. garden; OR: 1·72 (95% CI 1·20, 2·48)). Youth in higher density households vs. below median or living alone vs. with parents only also had greater odds of onset of low mental well-being (OR: 1·26 (95% CI 1·08, 1·46) and OR: 1·62 (95% CI 1·17, 2·23), respectively). Living in denser households (vs. below median; OR: 1·18 (95% CI 1·06, 1·33), as well as living alone (vs. with parents; OR: 1·38 (95% CI 1·04, 1·82) was associated with onset of low QoL. Living alone more than doubled odds of onset of loneliness compared to living with parents, OR: 2·12 (95% CI 1·59, 2·82). Youth living alone, in denser households, and without direct access to outdoor spaces may be especially vulnerable to mental health declines.

Cumulative Lactation and Clinical Metabolic Outcomes at Mid-Life among Women with a History of Gestational Diabetes

Lactation is associated with a lower risk of subsequent cardiometabolic disease among parous women; however, the underlying mechanisms are unknown. Further, the potential protective effects of lactation on cardiometabolic risk markers at mid-life among high-risk women with past gestational diabetes (GDM) are not established. Using data from the Diabetes & Women’s Health Study (2012−2014; n = 577), a longitudinal cohort of women with past GDM from the Danish National Birth Cohort (1996−2002), we assessed associations of cumulative lactation duration (none, <6 months, 6−12 months, ≥12−24 months, and ≥24 months) with clinical metabolic outcomes (including type 2 diabetes [T2D], prediabetes, and obesity) and cardiometabolic biomarkers (including biomarkers of glucose/insulin metabolism, fasting lipids, inflammation, and anthropometrics) 9−16 years after enrollment when women were at mid-life. At follow-up, women were 43.9 years old (SD 4.6) with a BMI of 28.7 kg/m2 (IQR 24.6, 33.0); 28.6% of participants had T2D, 39.7% had prediabetes, and 41.2% had obesity. Relative risks (95% CI) of T2D for 0−6, 6−12, 12−24, and ≥24 months of cumulative lactation duration compared to none were 0.94 (0.62,1.44), 0.88 (0.59,1.32), 0.73 (0.46,1.17), and 0.71 (0.40,1.27), respectively. Cumulative lactation duration was not significantly associated with any other clinical outcome or continuous biomarker. In this high-risk cohort of middle-aged women with past GDM, T2D, prediabetes, and obesity were common at follow-up, but not associated with history of cumulative lactation duration 9−16 years after the index pregnancy. Further studies in diverse populations among women at mid-age are needed to understand associations of breastfeeding with T2D.

Indoor home environments of Danish children and the socioeconomic position and health of their parents: A descriptive study

BACKGROUND

Housing and indoor home environments are associated with the risk of infections and asthma in children. To better understand the determinants and characteristics of these environments, we aimed to describe the associations between parental health and socioeconomic position and housing and indoor home environments of children in Denmark, and the clustering of the factors within these environments.

METHODS

Offspring in the Danish National Birth Cohort (DNBC) whose parents responded to the 11-year follow-up were eligible for inclusion. We included complete cases only. Data on the indoor and housing environments (i.e. variables on housing, sources of gaseous and particle pollution, mould and moisture, and pets) were collected through an online questionnaire responded to by a parent. Data on socioeconomic position were obtained through linkage with registry data on maternal education at offspring birth and household equivalized income at offspring birth. Data on parental health were obtained by linking self-reported data from the 11-year follow-up for mother and father with administrative registry data for the mother. We present descriptive statistics and exploratory factor analyses.

RESULTS

A total of 42 723 offspring were included for analyses. The distributions of nearly all indoor and housing environments differed according to educational and income strata, with patterns similar for both education and income. Generally, higher parental educational and income strata had more favorable indoor and housing environments (less secondhand smoking, gas stove use, mould and condensation and higher house ownership, detached house dwellings and newer building age). However, candle use was approximately similar between strata, fireplace use among lower educational and income strata tended towards the extremes (none or daily), and water damage was more common among higher educational and income strata. Parental health was strongly associated with housing and indoor home environment factors - especially parental affective disorders was strongly associated with mould. Four factors were extracted from the exploratory factor analyses, relating primarily in order of extraction to: housing ownership, mould and moisture, candle use and household density.

CONCLUSION

Parental health and socioeconomic position are strongly related to housing and indoor home environments. Additionally, several factors in these environments correlate strongly and cluster together. Observational studies on associations and causal effects of factors in the indoor and housing environments of children on their morbidity, must consider both of these conclusions to arrive at valid estimates and effects.

Prenatal antibiotic exposure and birth weight

BACKGROUND/OBJECTIVES

Current research suggests an association between antibiotic use in early life and later obesity. Less is known about prenatal antibiotic exposure and foetal growth. We investigated the association between prenatal antibiotic exposure and birth weight.

METHODS

Data from the Danish National Birth Cohort were linked to the Danish National Medical Birth Registry. Exposure was self-reported antibiotic use in pregnancy. Outcome was registered birth weight. Multivariable linear regression models were adjusted for confounders defined a priori.

RESULTS

A total of 63 300 mother-child dyads from 1996 to 2002 were included. Overall, prenatal antibiotic exposure was not associated with birth weight (-8.90 g, 95%CI: -19.5- +1.64 g, p = 0.10). Findings were similar for those born term and preterm. Antibiotic exposure in second to third trimester, compared to no exposure, was associated with lower birth weight (-12.6 g, 95%CI: -24.1 to -1.1 g, p = 0.03). In sex-stratified analyses, there were no observed associations between antibiotics and birth weight. With further stratifications, prenatal antibiotic exposure and birth weight were associated in boys who were preterm (+91.0 g, 95%CI: +6.8 g- +175.2 g, p = 0.03) but not among girls who were preterm (-44.0 g, 95%CI: -128.1 to +40.0 g, p = 0.30).

CONCLUSIONS

Prenatal antibiotic exposure is not consistently associated with birth weight.

Lifestyle in Pregnancy and Hypospadias in Sons: A Study of 85,923 Mother-Son Pairs from Two Danish Pregnancy Cohorts

Purpose

Hypospadias is one of the most frequent male congenital malformations. It remains controversial whether maternal lifestyle during pregnancy may affects the risk of having a son with hypospadias, especially for smoking with many suggesting lower risk. We assessed the individual and joint associations between maternal cigarette smoking, pre-pregnancy body mass index (BMI), alcohol consumption, binge drinking, and caffeine consumption and occurrence of hypospadias in sons.

Patients and Methods

This cohort study utilized the Danish National Birth Cohort and the Aarhus Birth Cohort, holding detailed information on lifestyle factors in early pregnancy between 1989 and 2012. The Danish health registers were used to identify boys with hypospadias, according to International Classification of Diseases. Potential confounders and covariates were identified by literature search and use of directed acyclic graphs. Missing data were handled by multiple imputation and Cox proportional hazards models were applied to analyse data.

Results

In total, 85,923 live-born singleton boys were included in the study of whom 502 (0.6%) were diagnosed with hypospadias. Maternal smoking in early pregnancy was associated with lower occurrence of hypospadias. An increase of one cigarette smoked per day was associated with lower risk of having a son with hypospadias (adjusted hazard ratio (HR) 0.97 (95% confidence interval (CI) 0.94, 1.00)). However, sub-analyses suggested that the results may be prone to unadjusted confounding. We found no association between pre-pregnancy BMI, alcohol consumption, binge drinking, or caffeine consumption and hypospadias.

Conclusion

Maternal smoking during pregnancy was associated with lower occurrence of hypospadias but we cannot exclude uncontrolled confounding. The other investigated maternal lifestyle factors were not associated with hypospadias in sons.