Residential exposure to mold, dampness, and indoor air pollution and risk of respiratory tract infections: a study among children ages 11 and 12 in the Danish National Birth Cohort

BACKGROUND

The burden of respiratory tract infections (RTIs) is high in childhood. Several residential exposures may affect relative rates.

OBJECTIVES

To determine risk of RTIs in children ages 11 and 12 by residential exposures.

METHODS

We included children in the Danish National Birth Cohort (DNBC) at ages 11 and 12. We estimated incidence risk ratios (IRR) and 95% confidence intervals (CI) for counts of RTIs within the last year by exposure to mold/dampness, gas stove usage, summer and winter candle-burning, fireplace usage, cats and dogs indoors, and farmhouse living. We also estimated IRR and 95% CI for RTIs for predicted scores of four extracted factors ('owned house', 'mold and dampness', 'candles', and 'density') from exploratory factor analyses (EFA).

RESULTS

We included 42 720 children with complete data. Mold/dampness was associated with all RTIs (common cold: IRRadj 1.09[1.07, 1.12]; influenza: IRRadj 1.10 [1.05, 1.15]; tonsillitis: IRRadj 1.19 [1.10, 1.28]; conjunctivitis: IRRadj 1.16 [1.02, 1.32]; and doctor-diagnosed pneumonia: IRRadj 1.05 [0.90, 1.21]), as was the EFA factor 'mold/dampness' for several outcomes. Gas stove usage was associated with conjunctivitis (IRRadj 1.25 [1.05, 1.49]) and with doctor-diagnosed pneumonia (IRRadj 1.14 [0.93, 1.39]). Candle-burning during summer, but not winter, was associated with several RTIs, for tonsillitis in a dose-dependent fashion (increasing weekly frequencies vs. none: [IRRadj 1.06 [0.98, 1.14], IRRadj 1.16 [1.04, 1.30], IRRadj 1.23 [1.06, 1.43], IRRadj 1.29 [1.00, 1.67], and IRRadj 1.41 [1.12, 1.78]).

CONCLUSION

Residential exposures, in particular to mold and dampness and to a lesser degree to indoor combustion sources, are related to the occurrence of RTIs in children.

Adherence to different forms of plant-based diets and pregnancy outcomes in the Danish National Birth Cohort: A prospective observational study

INTRODUCTION

The number of people adhering to plant-based diets has been increasing dramatically in recent years, fueled by both environmental and animal welfare concerns. Beneficial or possible adverse consequences of such diets, particularly the most restrictive forms during pregnancy, have been minimally explored. The aim of this prospective observational study was to examine associations between different forms of plant-based diets during pregnancy with birth outcomes and pregnancy complications.

MATERIAL AND METHODS

The Danish National Birth Cohort included 100 413 pregnancies to 91 381 women in 1996-2002. The population consisted of 66 738 pregnancies, about which sufficient dietary data were available and included in the study. Dietary and supplemental intake was assessed by Food Frequency Questionnaire in gestational week 25 and women were characterized as fish/poultry-vegetarians, lacto/ovo-vegetarians, vegans or omnivorous, based on their self-report in gestational week 30. Main outcome measures were pregnancy and birth complications, birth weight and small for gestational age.

RESULTS

A total of 98.7% (n = 65 872) of participants were defined as omnivorous, whereas 1.0% (n = 666), 0.3% (n = 183) and 0.03% (n = 18) identified themselves as fish/poultry vegetarians, lacto/ovo-vegetarians or vegans, respectively. Protein intake was lower among lacto/ovo-vegetarians (13.3%) and vegans (10.4%) than among omnivorous participants (15.4%). Intake of micronutrients was also considerably lower among vegans, but when dietary supplements were taken into consideration, no major differences were observed. Compared with omnivorous mothers, vegans had a higher prevalence of preeclampsia and their offspring had on average -240 g (95% confidence interval -450 to -30) lower birth weight.

CONCLUSIONS

The women reporting that they adhered to vegan diets during pregnancy had offspring with lower mean birth weight and higher risk of preeclampsia compared with omnivorous mothers. Low protein intake might be one plausible explanation for the observed association with birth weight.

Exposure to different residential indoor characteristics during childhood and asthma in adolescence: a latent class analysis of the Danish National Birth Cohort

BACKGROUND

Many residential indoor environments may have an impact on children's respiratory health.

OBJECTIVES

The aims of this study were to identify latent classes of children from the Danish National Birth Cohort (DNBC) who share similar patterns of exposure to indoor home characteristics, and to examine the association between membership in the latent classes and asthma in adolescence.

METHODS

We included data on residential indoor characteristics of offspring from the DNBC whose mothers had responded to the child's 11-year follow-up and who had data on asthma from the 18-year follow-up. Number of classes and associations were estimated using latent class analysis. To account for sample selection, we applied inverse probability weighting.

RESULTS

Our final model included five latent classes. The probability of current asthma at 18 years was highest among individuals in class one with higher clustering on household dampness (9, 95%CI 0.06-0.13). Individuals in class four (with higher clustering on pets ownership and living in a farm) had a lower risk of current asthma at age 18 compared to individuals in class one (with higher clustering on household dampness) (OR 0.53 (95%CI 0.32-0.88), p = .01).

CONCLUSION

Our findings suggest that, in a high-income country such as Denmark, groups of adolescents growing up in homes with mold and moisture during mid-childhood might be at increased risk of current asthma at age 18. Adolescents who grew-up in a farmhouse and who were exposed to pets seem less likely to suffer from asthma by age 18.

The influence of early-life animal exposure on the risk of childhood atopic dermatitis, asthma and allergic rhinoconjunctivitis: findings from the Danish National Birth Cohort

BACKGROUND

Early-life animal exposure has been associated with both protective and harmful effects on asthma and allergic disease. We aimed to explore factors that may modify associations of early-life animal exposure with asthma and allergic disease, so as to better understand these differences in findings.

METHODS

We used data from ≤84 478 children from the Danish National Birth Cohort recruited during pregnancy between 1996 and 2002, and linked registry data up to the child's 13th birthday. Adjusted Cox models were used to examine associations of early-life cat, dog, rabbit, rodent, bird and livestock exposure with atopic dermatitis, asthma and allergic rhinoconjunctivitis overall, and by source of exposure (domestic or occupation), parental history of asthma or allergy, maternal education level and timing of exposure.

RESULTS

Overall, associations between animal exposure and the three outcomes of interest were weak. However, dog exposure was associated with marginally lower risk of atopic dermatitis and asthma [adjusted hazard ratio (aHR) = 0.81, 95% CI: 0.70-0.94 and 0.88, 95% CI: 0.82-0.94, respectively], whereas prenatal domestic bird exposure was associated with slightly increased risk of asthma (aHR = 1.18, 95% CI: 1.05-1.32). Source of exposure, parental history of asthma or allergy and timing of exposure modified associations. Early-life animal exposure did not appear to increase the risk of allergic rhinoconjunctivitis (aHR range = 0.88, 95% CI: 0.81-0.95 to 1.00, 95% CI: 0.91-1.10).

CONCLUSIONS

The overall weak associations observed between animal exposure and atopic dermatitis, asthma and allergic rhinoconjunctivitis were modified by type of animal, source of exposure, parental history of asthma or allergy and timing of exposure, suggesting that these factors should be considered when assessing the risks associated with early-life animal exposure.

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.

Menstrual pain and sexual health in mothers-A cross-sectional study in the Danish National Birth Cohort

INTRODUCTION

Prevalence and consequences of menstrual pain have mainly been studied in younger women. We aimed to describe the prevalence of menstrual pain in mothers and its association with sexual problems.

MATERIAL AND METHODS

A cross-sectional study using questionnaire data from the Maternal Follow Up (2013-2014) in the Danish National Birth Cohort (1996-2002). Of 82 569 eligible mothers, 43 639 (53%) completed the follow up. Of these, 24 000 women had a partner, and answered the questions on menstrual pain. Log binomial regression was used to calculate prevalence proportion ratios (PPR) with 95% CI for the association between menstrual pain and specific sexual problems.

RESULTS

Menstrual pain was reported by 16 464 women (69%), and severe menstrual pain by 19%. Treatment had previously been requested by 19% of women with menstrual pain. The most common treatment was oral contraceptives, but for 18% of women seeking treatment, no treatment was given. Women with menstrual pain were more likely to report reduced sexual desire (PPR 1.22, 95% CI 1.15-1.29), vaginismus (PPR 1.31, 95% CI 0.96-1.78), and dyspareunia (PPR 1.63, 95% CI 1.47-1.81), in particular deep dyspareunia (PPR 1.92, 95% CI 1.67-2.20).

CONCLUSIONS

A majority of Danish mothers in mid-life experienced menstrual pain, and these women more often reported reduced sexual desire, vaginismus, and deep dyspareunia. Few women sought and received treatment for menstrual pain. Healthcare practitioners should be aware that menstrual pain can affect parous women and co-occurs with sexual problems. Future studies should identify barriers to seeking and receiving adequate treatment for menstrual pain.

The Confounder-Mediator Dilemma: Should We Control for Obesity to Estimate the Effect of Perfluoroalkyl Substances on Health Outcomes?

Confounding adjustment is important for observational studies to derive valid effect estimates for inference. Despite the theoretical advancement of confounding selection procedure, it is often challenging to distinguish between confounders and mediators due to the lack of information about the time-ordering and latency of each variable in the data. This is also the case for the studies of perfluoroalkyl substances (PFAS), a group of synthetic chemicals used in industry and consumer products that are persistent and have endocrine-disrupting properties on health outcomes. In this article, we used directed acyclic graphs to describe potential biases introduced by adjusting for or stratifying by the measure of obesity as an intermediate variable in PFAS exposure analyses. We compared results with or without adjusting for body mass index in two cross-sectional data analyses: (1) PFAS levels and maternal thyroid function during early pregnancy using the Danish National Birth Cohort and (2) PFAS levels and cardiovascular disease in adults using the National Health and Nutrition Examination Survey. In these examples, we showed that the potential heterogeneity observed in stratified analyses by overweight or obese status needs to be interpreted cautiously considering collider stratification bias. This article highlights the complexity of seemingly simple adjustment or stratification analyses, and the need for careful consideration of the confounding and/or mediating role of obesity in PFAS studies.

Dietary glycemic index and glycemic load during pregnancy and offspring risk of congenital heart defects: a prospective cohort study

BACKGROUND

Prepregnancy diabetes, especially when severely dysregulated, is associated with an increased risk of congenital heart defects in offspring. This suggests that glucose plays a role in embryonic heart development.

OBJECTIVE

The aim was to investigate the association between midpregnancy dietary glycemic index (GI), glycemic load (GL), and sugar-sweetened beverages and the risk of congenital heart defects in the offspring.

METHODS

Offspring of mothers from the Danish National Birth Cohort who filled out a food-frequency questionnaire (FFQ) covering midpregnancy dietary intake were included. Individual-level information on GI and GL, offspring congenital heart defects, and health and lifestyle covariates was linked. The association between GI and GL and offspring congenital heart defects was estimated by logistic regression. Further, we evaluated whether maternal intake of sugar-sweetened drinks increased the risk of offspring congenital heart defects.

RESULTS

In total, 66,387 offspring of women who responded to the FFQ were included; among offspring, 543 had a congenital heart defect. The adjusted OR (aOR) of congenital heart defects among offspring of mothers belonging to the highest versus the lowest GI quintile was 1.02 (95% CI: 0.78, 1.34; P-trend = 0.86). Results were similar for GL (aOR: 0.95; 95% CI: 0.72, 1.24). A high intake of sugar-sweetened carbonated beverages was associated with a statistically significant increased risk of offspring congenital heart defects (highest vs lowest intake-aOR: 2.41; 95% CI: 1.26, 4.64; P-trend = 0.03). No association was found with other types of beverages.

CONCLUSIONS

The study does not support an association between a high GI and GL in midpregnancy and increased offspring risk of congenital heart defects. Nevertheless, a statistically significant association between sugar-sweetened carbonated beverages and a moderately increased risk of offspring congenital heart defects was observed.

Mode of birth and long-term sexual health: a follow-up study of mothers in the Danish National Birth Cohort

OBJECTIVES

To investigate the relation between mode of birth and women's long-term sexual health.

DESIGN

Maternal follow-up of the Danish National Birth Cohort (1996-2002) in 2013-2014 including questions on sexual health. Logistic regression was used to relate registry-based information about mode of birth and perineal tears with data on sexual problems.

SETTING

Denmark.

PARTICIPANTS

Of 82 569 eligible mothers in the Danish National Birth Cohort, 43 639 (53%) completed the follow-up. Of these, 37 417 women had a partner, and answered at least one question on sexual health.

MAIN OUTCOME MEASURES

Self-reported sexual health.

RESULTS

Participants were on average 44 years old, and 16 years after their first birth. The frequency of sexual problems among women with only spontaneous vaginal births, the reference group, was 37%. For women who only had caesarean sections, more problems were reported (OR 1.18; 95% CI 1.09 to 1.28). For women who had a spontaneous vaginal birth subsequent to a caesarean, and for women with only vaginal births who had experienced one or more instrumental vaginal births, the odds of sexual problems did not differ from women with only spontaneous vaginal births (OR 1.00; 95% CI 0.91 to 1.11) and (OR 1.01; 95% CI 0.95 to 1.08), respectively.

CONCLUSIONS

These findings indicate that caesarean section does not protect against long-term sexual problems. Rather, vaginal birth, even after caesarean section, was associated with fewer long-term sexual problems.

Comparisons of Estimated Intakes and Plasma Concentrations of Selected Fatty Acids in Pregnancy

The growing interest in potential health effects of long-chain polyunsaturated fatty acids (PUFAs) makes it important to evaluate the method used to assess the fatty acid intake in nutrition research studies. We aimed to validate the questionnaire-based dietary intake of selected PUFAs: eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), α-linolenic acid (ALA), linoleic acid (LA), and arachidonic acid (AA) within the Danish National Birth Cohort (DNBC), by comparing 345 women’s reported intake with concentration of plasma biomarkers. The applied questionnaire- and biomarker data reflect dietary intake from around the same time point in mid-pregnancy and relationships were investigated by use of Pearson and Spearman correlation and linear regression statistics. We demonstrated moderate but consistent adjusted correlations between dietary intake estimates and the corresponding plasma biomarker concentrations (differences in plasma concentration per 100 mg/day greater intake of 0.05 (95% CI: 0.02; 0.08)) and 0.05 (95% CI: 0.01; 0.08) percentage of total plasma fatty acids for EPA and DHA, respectively). The associations strengthened when restricting the analyses to women with ALA intake below the median intake. We found a weak correlation between the dietary intake of ALA and its plasma biomarker with a difference in plasma concentration of 0.07 (95% CI: 0.03; 0.10) percent of total plasma fatty acids per 1 g/day greater intake, while the dietary intake of LA and AA did not correlate with their corresponding biomarkers.

Mental health among children of mothers with multiple sclerosis: A Danish cohort and register-based study

BACKGROUND

Multiple sclerosis is associated with an increased risk of developing physical, cognitive, and mental health problems. Current studies have demonstrated variating outcomes of parental multiple sclerosis mental health problems and their children's mental health development.

OBJECTIVE

The purpose of this study was to investigate whether maternal multiple sclerosis is associated with the mental health status of their child.

METHODS

Data from the Danish National Birth Cohort (DNBC) were merged with information from the Danish Multiple Sclerosis Registry. Two proxies, total difficulties score and prediction of any psychiatric diagnosis based on the strengths and difficulties questionnaire, were used to measure the mental health status of the children. The two groups were compared using Mann-Whitney and logistic regression analyses.

RESULTS

For the total difficulties score the control and exposed group consisted of respectively n = 42,016 and n = 40, and for the prediction of any psychiatric diagnosis respectively n = 16,829 and n = 17. We found no statistically significant association between maternal multiple sclerosis and mental health status on neither of the proxies.

CONCLUSION

Maternal multiple sclerosis did not show any association with the mental health status of their children at age eleven. On the contrary, other studies conclude that there is an association between maternal multiple sclerosis and the child's mental health status, one especially mediated by the maternal mental health status.

Prenatal Exposure to Perfluoroalkyl Substances and Birth Outcomes; An Updated Analysis from the Danish National Birth Cohort

Perfluoroalkyl substances (PFASs) are widespread industrial pollutants that are extremely persistent in the environment. A previous study in the Danish National Birth Cohort (DNBC) found prenatal perfluorooctanoate (PFOA) exposure was associated with decreased birth weight, but had insufficient statistical power to evaluate adverse birth outcomes. Here, we conducted additional analyses in three samples originating from the DNBC for 3535 mothers and infant pairs to evaluate associations between prenatal PFASs exposures and low birth weight and preterm birth. Maternal plasma concentrations were measured for six types of PFASs in early pregnancy. Several PFASs were associated with a reduction in birth weight and gestational age. We estimated a nearly 2-fold increase in risks of preterm birth for the higher quartiles of PFOA and perflourooctanesulfonate (PFOS) exposure. In spline models, risk of preterm birth was increased for perfluorononanoic acid (PFNA), perfluoroheptane sulfonate (PFHpS) and perfluorodecanoic acid (PFDA) in higher exposure ranges. We also observed some elevated risks for low birth weight but these estimates were less precise. Our findings strengthen the evidence that in-utero PFASs exposures affect fetal growth. Future studies are needed to evaluate whether these associations persist with the decline of PFOA and PFOS in populations and should also investigate newer types of fluorinated compounds introduced more recently.

Plasma Concentrations of Long Chain N-3 Fatty Acids in Early and Mid-Pregnancy and Risk of Early Preterm Birth

Background

Fish oil supplementation has been shown to delay spontaneous delivery, but the levels and clinical significance remain uncertain. We examined the association between plasma fatty acids quantified in pregnancy and subsequent risk of early preterm birth.

Methods

In a case-control design nested in the Danish National Birth Cohort, we identified 376 early preterm cases (<34 gestational weeks, excluding preeclampsia cases) and 348 random controls. Plasma eicosapentaenoic acid plus docosahexaenoic acid (EPA+DHA% of total fatty acids), were measured twice in pregnancy, at gestation weeks 9 and 25 (medians). Odds ratios and 95% confidence intervals (CI's) for associations between EPA+DHA and early preterm risk were estimated by logistic regression, adjusted for the woman's age, height, pre-pregnancy BMI, parity, smoking, and socioeconomic factors. Hypotheses and analytical plan were defined and archived a priori.

Findings

Analysis using restricted cubic splines of the mean of 1st and 2nd sample measurements showed a strong and significant non-linear association (p < 0.0001) in which the risk of early preterm birth steeply increased when EPA+DHA concentrations were lower than 2% and flattened out at higher levels. Women in the lowest quintile (EPA+DHA < 1.6%) had 10.27 times (95% confidence interval 6.80–15.79, p < 0.0001) increased risk, and women in the second lowest quintile had 2.86 (95% CI 1.79–4.59, p < 0.0001) times increased risk, when compared to women in the three aggregated highest quintiles (EPA+DHA ≥ 1.8%).

Interpretation

Low plasma concentration of EPA and DHA during pregnancy is a strong risk factor for subsequent early preterm birth in Danish women.

Childcare before age 6 and body mass index at age 7 years in a cohort of Danish children

BACKGROUND

Previous studies show inconsistent associations between childcare and obesity.

AIMS

Our prior work demonstrated that childcare in infancy was associated with higher weight in a cohort of Danish children. Here, we extend this work and examine childcare through 6 years and body mass index (BMI) at age 7 years.

MATERIALS AND METHODS

We examined 24 714 children in the Danish National Birth Cohort who were also in the Childcare Database. We conducted multivariable linear regressions examining children prior to age 6, overall and by type (daycare, crèche, age-integrated and kindergarten), and BMI z-score at 7 years, stratifying on maternal socio-occupational status.

RESULTS

A total of 19 760 (80.0%) children attended childcare before age 6. Childcare prior to age 6 was associated with BMI z-score at 7 years (0.004 units per each additional 6 months of care; 95% CI: 0.001, 0.008; p = 0.01). Childcare in a kindergarten was the only type of care associated with BMI (0.009 units; 95% CI: 0.003, 0.02; p = 0.01). For children of higher socio-occupational status mothers, childcare was associated with a 0.008 unit increase in BMI (95% CI: 0.004, 0.01; p > 0.001).

CONCLUSIONS

Childcare was weakly associated with later BMI. This relationship was more pronounced in children from higher socio-occupational status mothers and children in kindergarten care.

Maternal Thyroid Function in Early Pregnancy and Child Neurodevelopmental Disorders: A Danish Nationwide Case-Cohort Study

BACKGROUND

Maternal thyroid dysfunction may adversely affect fetal brain development, but more evidence is needed to refine this hypothesis. The aim of this study was to evaluate potential fetal programming by abnormal maternal thyroid function on child neurodevelopmental disorders.

METHODS

The design was a case-cohort study within the Danish National Birth Cohort (1997-2003). From the eligible cohort of 71,706 women, a random 12% sub-cohort (n = 7624) was selected, and all women (n = 2276) whose child was diagnosed with seizures, specific developmental disorder (SDD), autism spectrum disorder (ASD), and/or attention-deficit/hyperactivity disorder (ADHD) up to December 31, 2010, were identified. All women had a blood sample drawn in early pregnancy (median week 9), and the stored sample was used for measurement of free thyroxine and thyrotropin. Method- and week-specific reference ranges were used for classification of maternal thyroid function. A weighted Cox proportional hazards model was used to estimate adjusted hazard ratio (aHR) with 95% confidence intervals (CI) for neurodevelopmental disorders in children exposed to maternal thyroid dysfunction.

RESULTS

The overall frequency of abnormal maternal thyroid function was 12.5% in the sub-cohort and significantly higher among cases of ASD (17.9%; aHR = 1.5 [CI 1.1-2.1]), but not among other types of neurodevelopmental disorders (febrile seizures: 12.7%; epilepsy: 13.1%; SDD: 12.6%; and ADHD: 14.0%). However, evaluation of subtypes of maternal thyroid dysfunction showed that maternal overt hypothyroidism (thyrotropin >10 mIU/L) was a risk factor for epilepsy in the child (aHR = 3.5 [CI 1.2-10]), as was overt hyperthyroidism for cases diagnosed within the first year of life (aHR = 3.0 [CI 1.03-8.4]). Furthermore, both maternal hypothyroidism (aHR = 1.8 [CI 1.1-2.7]) and overt hyperthyroidism (aHR = 2.2 [CI 1.1-4.4]) were risk factors for ASD in the child, and isolated low free thyroxine was associated with ASD (aHR = 4.9 [CI 2.03-11.9]) and ADHD (aHR = 2.3 [CI 1.2-4.3]) in girls but not in boys.

CONCLUSIONS

Abnormal maternal thyroid function in early pregnancy was associated with epilepsy, ASD, and ADHD in the child, but associations differed by subtypes of exposure and by child age and sex. More evidence on subtypes and severity of maternal thyroid function is needed, and alternative outcomes of child neurodevelopment may be warranted.

Age at Menarche and Risk of Multiple Sclerosis: A Prospective Cohort Study Based on the Danish National Birth Cohort

Few studies have addressed the possible association between age at menarche and multiple sclerosis (MS), and results are conflicting. We studied this issue in a large prospective cohort study. The study cohort comprised 77,330 women included in the Danish National Birth Cohort (1996-2002). Information on menarcheal age was ascertained at the first interview, which took place in the 16th week of pregnancy. Women were followed for MS from the first interview to December 31, 2011. Associations between age at menarche and risk of MS were evaluated with hazard ratios and 95% confidence intervals using Cox proportional hazards regression models. Overall, 226 women developed MS during an average follow-up period of 11.7 years. Age at menarche among women with MS was generally lower than that among women without MS (Wilcoxon rank-sum test; P = 0.002). We observed an inverse association between age at menarche and MS risk. For each 1-year increase in age at menarche, risk of MS was reduced by 13% (hazard ratio = 0.87, 95% confidence interval: 0.79, 0.96). Early age at menarche appears to be associated with an increased risk of MS. The mechanisms behind this association remain to be established.

Early Pregnancy Thyroid Function Test Abnormalities in Biobank Sera from Women Clinically Diagnosed with Thyroid Dysfunction Before or After Pregnancy

BACKGROUND

Maternal thyroid disease may complicate pregnancy. A high frequency of abnormal thyroid function test results in pregnant women with known thyroid disease has been reported, but the frequency of unidentified thyroid dysfunction in women first clinically diagnosed with thyroid disease after a pregnancy is not known.

METHODS

This was a population-based study of pregnant women in the Danish National Birth Cohort (DNBC) who had a blood sample drawn in early pregnancy and terminated the pregnancy with a singleton live-birth in the period between 1997 and 2003. Participants were all women in the DNBC who had a registration of thyroid disease before and/or up to five years after the pregnancy in nationwide health registers (n = 2445) and a 12% random sample of all women in the cohort (n = 7624). Thyrotropin and free thyroxine were measured with an immunoassay in sera stored in the Danish National Biobank. Method- and pregnancy week-specific references ranges were used for classification of thyroid function test abnormalities.

RESULTS

The frequency of abnormal thyroid function in early pregnancy was 12.5% in the random sample and 35.7% among women clinically diagnosed with thyroid disease before or after blood sampling (55.7% among women on current treatment). One third of women clinically diagnosed with thyroid disease after blood sampling had unidentified thyroid dysfunction in the early pregnancy blood sample (most frequently [52.0%] unidentified hypothyroidism in women with a later diagnosis of hypothyroidism).

CONCLUSIONS

More than 50% of Danish pregnant women on current treatment for thyroid disease had thyrotropin and/or free thyroxine outside the week-specific reference ranges, and the frequency of unidentified early pregnancy thyroid dysfunction in women clinically diagnosed after the pregnancy was also high.

Childhood psychopathology in children of women with eating disorders

OBJECTIVE

We aimed to investigate the effect of maternal eating disorders (ED) on childhood psychopathology, early delays in cognitive, motor and language development, mother and child relationship, and child temperament in a community-based cohort: the Danish National Birth Cohort (DNBC).

METHOD

Data were obtained prospectively on 48 403 children at 18 months and 46 156 children at 7 years. Data on cognitive, motor and language development, temperament and attachment were obtained at 18 months; data on child psychopathology were obtained at 7 years of age, using the Strengths and Difficulties Questionnaire (SDQ). Children of mothers with lifetime diagnosis of anorexia nervosa (AN, n = 931), lifetime diagnosis of bulimia nervosa (BN, n = 906) and both (AN & BN = 360) were compared to children of mothers without an ED (n = 46 206).

RESULTS

Girls of women with lifetime AN had higher odds of having emotional problems, and girls of women with lifetime BN of having conduct problems compared with children of healthy women. Boys of women with lifetime AN had higher odds of total, emotional and conduct problems; boys of women with lifetime BN had higher odds of total, conduct, hyperactivity and peer difficulties compared to children of women without an ED. Boys of women with lifetime AN and BN had higher odds of total, emotional and peer problems compared to children of healthy women.

CONCLUSION

Maternal ED is associated with childhood psychopathology in both boys and girls. Boys seemed at higher risk for psychopathology in this sample. Associations between emotional disorders across genders in children of mothers with lifetime AN, and hyperactivity and peer difficulties in boys of mothers with lifetime BN confirm and extend previous findings and point to possible shared risk between ED and other psychopathology.

Developmental milestones in children born post-term in the Danish National Birth Cohort: a main research article

OBJECTIVE

To examine the timing of reaching developmental milestones in children born post-term.

DESIGN

Cohort study.

SETTING

The Danish National Birth Cohort: children born between 1997 and 2003.

POPULATION

Data were obtained from a cohort of 92 892 pregnancies participating in the first pregnancy interview. All singletons born in gestational weeks 39-45 were identified. The study was then restricted to children who participated in an interview at the age of approximately 18 months and had information on at least one developmental milestone. We excluded children of mothers with chronic diseases from the final analysis. The remaining study population constituted of 43 915 singletons (27 503 born at term; 16 412 born post-term).

METHODS

Logistic regression was used to calculate odds ratios of late achievement of these developmental milestones, adjusted for potential confounding factors.

MAIN OUTCOME MEASURES

Achieving developmental milestones at the time of interview or at a certain age.

RESULTS

More children born post-term achieved the assessed developmental milestones compared with children born at term (39-40 weeks). A test for trend for gestational ages 39, 40, and 41 weeks also showed a positive trend at achieving developmental milestones with gestational age at birth in nine out of 14 milestone items.

CONCLUSIONS

Children born post-term appear to reach the main developmental milestones at an earlier age than children born at term. The association could also result from bias related to a longer time between conception and interviewing, misclassification of end points, or selection bias.

Childhood epilepsy and maternal antibodies to microbial and tissue antigens during pregnancy

INTRODUCTION

Several epidemiologic studies show associations between mother's infections during pregnancy and an increased risk of mental and neurological disorders in the offspring. Such associations could be due to the direct or indirect effects of infectious agents, including immune responses to infectious agents that display molecular mimicry with host antigens. We measured a range of antigen-specific maternal IgG antibodies to examine if any were associated with risk for childhood epilepsy in offspring.

METHODS

We used a case-cohort design within the Danish National Birth Cohort (DNBC) to examine maternal IgG antibodies to 25 microbial and tissue antigens during pregnancy and their association with the risk of epilepsy in offspring. The source population of this study was 68,250 live born singletons with up to 10 years of follow up. We randomly identified a sample of 282 children as a subcohort and included 275 children with a verified diagnosis of epilepsy as cases. Maternal antibodies were categorized into 6 groups (<50, 50-59, 60-69, 70-79, 80-89, ≥90 percentile) according to the level in the subcohort. We used a Prentice-weighted Cox regression model to estimate the hazard ratio (HR) and 95% confidence interval (CI) for epilepsy according to measured antibodies.

RESULTS

Higher levels of maternal antibodies against herpes simples virus type 1 (anti-HSV1) were associated with a slightly higher risk of childhood epilepsy (HR for trend=1.09, 95% CI: 0.99-1.21), while higher levels of maternal antibodies against pneumococcal polysaccharide 18 (anti-PnPS18) were associated with a lower risk of childhood epilepsy (HR for trend=0.90, 95% CI: 0.81-1.01). Among the subtypes, a significantly higher risk associated with anti-HSV1 antibodies was seen for childhood absence epilepsy (HR for trend=2.08, 95% CI: 1.12-3.85) and for epileptic encephalopathies (HR for trend=1.49, 95% CI: 1.01-2.22). The significantly lower risk associated with anti-PnPS18 antibodies was observed for infantile spasms (HR for trend=0.47, 95% CI: 0.27-0.83).

CONCLUSIONS

Maternal anti-HSV1and anti-PnPS18 antibodies during pregnancy may be associated with the risk of epilepsy in offspring, but any potential etiologic and preventative implications of these associations warrant further exploration.