Early or late menarche is associated with reduced fecundability in the Norwegian Mother, Father and Child Cohort Study

STUDY QUESTION

Is age at menarche associated with fecundability?

SUMMARY ANSWER

Both early (<11 years) and late (>15 years) menarche is associated with decreased fecundability.

WHAT IS KNOWN ALREADY

Previous studies on age at menarche and fecundability have been inconclusive. Women with early or late menarche are at increased risks of gynaecological and autoimmune diseases that may affect their ability to conceive.

STUDY DESIGN, SIZE, DURATION

We conducted a retrospective cohort study including 67 613 pregnant women, participating in the Norwegian Mother, Father and Child Cohort Study between 1999 and 2008, with self-reported information on age at menarche and time to pregnancy. We included planned pregnancies that were conceived either naturally or with the help of assisted reproductive technologies.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We calculated fecundability ratios (FRs) with 95% CIs representing the cycle-specific probability of conception by categories of age at menarche. FRs were adjusted for participants' pre-pregnancy body mass index, highest completed or ongoing education level, and age at initiation of trying to conceive.

MAIN RESULTS AND THE ROLE OF CHANCE

We observed a 7% lower probability of conceiving during any given menstrual cycle up to 12 cycles in women with early or late menarche. Among women with menarche >15 years, the adjusted FR was 0.93 (95% CI: 0.90-0.97), and among women with menarche <11 years, the adjusted FR was 0.93 (95% CI: 0.89-0.99), when compared to women with menarche between 12 and 14 years.

LIMITATIONS, REASONS FOR CAUTION

The study-population consisted of women pregnant in their second trimester, excluding those with persistent infertility. Recall of age at menarche and time to pregnancy may be inaccurate.

WIDER IMPLICATIONS OF THE FINDINGS

Both early (<11 years) and late (>15 years) menarche was associated with decreased fecundability. Women experiencing early menarche or late menarche may be counselled accordingly.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by the Norwegian Institute of Public Health, Oslo, Norway, and by Telemark Hospital Trust, Porsgrunn, Norway and was partly supported by the Research Council of Norway through its centres of excellence funding scheme (project number 262700) and the Research Council of Norway (project no. 320656). The project was co-funded by the European Union (ERC, BIOSFER, 101071773). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. M.C.M. has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement no. 947684). The authors report no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Paternal and maternal birthweight and offspring risk of macrosomia at term gestations: A nationwide population study

BACKGROUND

There is a paucity of data on whether parents' macrosomia (birthweight ≥4500 g) status influences the risk of macrosomia in the offspring. The role of maternal overweight in the generational effect of macrosomia is not known.

OBJECTIVE

To estimate the risk of macrosomia by parental birthweight at term and evaluate if this risk varied with maternal body mass index (BMI, kg/m2) early in pregnancy.

METHODS

We used data from the Medical Birth Registry of Norway on all singleton term births (37-42 gestational weeks) during 1967-2017. The primary exposure was parental macrosomia, and the outcome was macrosomia in the second generation. The secondary exposure was maternal BMI. We used binomial regression to calculate relative risk (RR) with a 95% confidence interval. We assessed potential unmeasured confounding and selection bias using a probabilistic bias analysis and performed analyses with and without imputation for variables with missing values.

RESULTS

The data included 647,957 singleton parent-offspring trios born at term. The prevalence of macrosomia was 3.2% (n = 41,396) in the parental generation and 4.0% (n = 25,673) in the offspring generation. Macrosomia in parents was associated with an increased risk of macrosomia in offspring, with the RR for both parents were born macrosomic being 6.53 (95% confidence interval [CI] 5.31, 8.05), only mother macrosomic 3.37 (95% CI 3.17, 3.57) and only father macrosomic RR 2.22 (95% CI 2.12, 2.33). These risks increased by maternal BMI in early pregnancy: if both parents were born macrosomic, 17% of infants were macrosomic among mothers with normal BMI. If both parents were macrosomic and the mothers were obese, 31% of offspring were macrosomic. Macrosomia-related adverse outcomes did not differ with parental macrosomia status.

CONCLUSIONS

Parents' weight at birth and maternal BMI appear to be strongly associated with macrosomia in the offspring delivered at term gestations.

A Pregnancy and Childhood Epigenetics Consortium (PACE) meta-analysis highlights potential relationships between birth order and neonatal blood DNA methylation

Higher birth order is associated with altered risk of many disease states. Changes in placentation and exposures to in utero growth factors with successive pregnancies may impact later life disease risk via persistent DNA methylation alterations. We investigated birth order with Illumina DNA methylation array data in each of 16 birth cohorts (8164 newborns) with European, African, and Latino ancestries from the Pregnancy and Childhood Epigenetics Consortium. Meta-analyzed data demonstrated systematic DNA methylation variation in 341 CpGs (FDR adjusted P < 0.05) and 1107 regions. Forty CpGs were located within known quantitative trait loci for gene expression traits in blood, and trait enrichment analysis suggested a strong association with immune-related, transcriptional control, and blood pressure regulation phenotypes. Decreasing fertility rates worldwide with the concomitant increased proportion of first-born children highlights a potential reflection of birth order-related epigenomic states on changing disease incidence trends.

Maternal pre-pregnancy body mass index and risk of preterm birth: a collaboration using large routine health datasets

BACKGROUND

Preterm birth (PTB) is a leading cause of child morbidity and mortality. Evidence suggests an increased risk with both maternal underweight and obesity, with some studies suggesting underweight might be a greater factor in spontaneous PTB (SPTB) and that the relationship might vary by parity. Previous studies have largely explored established body mass index (BMI) categories. Our aim was to compare associations of maternal pre-pregnancy BMI with any PTB, SPTB and medically indicated PTB (MPTB) among nulliparous and parous women across populations with differing characteristics, and to identify the optimal BMI with lowest risk for these outcomes.

METHODS

We used three UK datasets, two USA datasets and one each from South Australia, Norway and Denmark, together including just under 29 million pregnancies resulting in a live birth or stillbirth after 24 completed weeks gestation. Fractional polynomial multivariable logistic regression was used to examine the relationship of maternal BMI with any PTB, SPTB and MPTB, among nulliparous and parous women separately. The results were combined using a random effects meta-analysis. The estimated BMI at which risk was lowest was calculated via differentiation and a 95% confidence interval (CI) obtained using bootstrapping.

RESULTS

We found non-linear associations between BMI and all three outcomes, across all datasets. The adjusted risk of any PTB and MPTB was elevated at both low and high BMIs, whereas the risk of SPTB was increased at lower levels of BMI but remained low or increased only slightly with higher BMI. In the meta-analysed data, the lowest risk of any PTB was at a BMI of 22.5 kg/m2 (95% CI 21.5, 23.5) among nulliparous women and 25.9 kg/m2 (95% CI 24.1, 31.7) among multiparous women, with values of 20.4 kg/m2 (20.0, 21.1) and 22.2 kg/m2 (21.1, 24.3), respectively, for MPTB; for SPTB, the risk remained roughly largely constant above a BMI of around 25-30 kg/m2 regardless of parity.

CONCLUSIONS

Consistency of findings across different populations, despite differences between them in terms of the time period covered, the BMI distribution, missing data and control for key confounders, suggests that severe under- and overweight may play a role in PTB risk.

Maternal pre-pregnancy BMI and reproductive health in adult sons: a study in the Danish National Birth Cohort

STUDY QUESTION

Is maternal pre-pregnancy BMI associated with semen quality, testes volume, and reproductive hormone levels in sons?

SUMMARY ANSWER

Maternal pre-pregnancy BMI was associated with an altered reproductive hormone profile in young adult sons, characterized by higher levels of oestradiol, LH, and free androgen index (FAI) and lower levels of sex hormone-binding globulin (SHBG) in sons born of mothers with pre-pregnancy overweight and obesity.

WHAT IS KNOWN ALREADY

Evidence suggests that maternal pre-pregnancy BMI may influence reproductive health later in life. Only one pilot study has investigated the association between maternal pre-pregnancy BMI and reproductive health outcomes in sons, suggesting that a high BMI was associated with impaired reproductive function in the adult sons.

STUDY DESIGN, SIZE, DURATION

A population-based follow-up study of 1058 young men from the Fetal Programming of Semen Quality (FEPOS) cohort nested within the Danish National Birth Cohort (DNBC), 1998-2019, was carried out.

PARTICIPANTS/MATERIALS, SETTING, METHODS

In total, 1058 adult sons (median age 19 years, 2 months), born 1998-2000 by mothers included in the DNBC, participated in FEPOS. At a clinical examination, they provided a semen and blood sample, measured their testes volume, and had height and weight measured. Maternal pre-pregnancy BMI was obtained by self-report in early pregnancy. Semen characteristics, testes volume, and reproductive hormone levels were analysed according to maternal pre-pregnancy BMI categories and as restricted cubic splines using negative binomial and ordinary least square regression models. Mediation analyses examined potential mediation by the sons' birthweight, pubertal timing, fat mass, and BMI. Additional analyses investigated the role of paternal BMI in the potential associations between maternal BMI and reproductive health outcomes.

MAIN RESULTS AND THE ROLE OF CHANCE

We found no consistent associations between maternal pre-pregnancy BMI and semen characteristics or testes volume. Sons of mothers with higher pre-pregnancy BMI had higher oestradiol and lower SHBG levels, both in a dose-dependent manner. Sons of mothers with pre-pregnancy obesity (≥30 kg/m2) had higher LH levels and a higher FAI than sons born by mothers with normal pre-pregnancy BMI (18.5-24.9 kg/m2). The mediation analyses suggested that the effect of maternal pre-pregnancy BMI on higher levels of oestrogen, LH, and FAI was partly mediated by the sons' birthweight, in addition to adult fat mass and BMI measured at the clinical examination, whereas most of the effect on lower levels of SHBG was primarily mediated by the sons' own fat mass and BMI. Paternal BMI was not a strong confounder of the associations in this study.

LIMITATIONS, REASONS FOR CAUTION

This study was based in a population-based cohort with a low prevalence of overweight and obesity in both mothers and adult sons. Some men (10%) had blood for reproductive hormone assessment drawn in the evening. While several potential confounding factors were accounted for, this study's inherent risk of residual and unmeasured confounding precludes provision of causal estimates. Therefore, caution should be given when interpreting the causal effect of maternal BMI on sons' reproductive health.

WIDER IMPLICATIONS OF THE FINDINGS

Given the widespread occurrence of overweight and obesity among pregnant women, it is imperative to thoroughly examine the potential consequences for reproductive hormone levels in adult sons. The potential effects of maternal pre-pregnancy obesity on sons' reproductive hormone profile may potentially be partly avoided by the prevention of overweight and obesity in the sons.

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, Independent Research Fund Denmark (9039-00128B), and the European Union (ERC, BIOSFER, 101071773). Views and opinions expressed are, however, those of the authors only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible. The authors declare that they have no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

Prevalence and predictors of post-COVID-19 symptoms in general practice - a registry-based nationwide study

BACKGROUND

With Norwegian national registry data, we assessed the prevalence of post-COVID-19 symptoms at least 3 months after confirmed infection, and whether sociodemographic factors and pre-pandemic health problems were risk factors for these symptoms.

METHODS

All persons with a positive SARS-CoV-2 PCR test from February 2020 to February 2021 (exposed) were compared to a group without a positive test (unexposed) matched on age, sex, and country of origin. We used Cox regression to estimate hazard ratios (HR) for 18 outcome symptoms commonly described as post-COVID-19 related, registered by GPs. We compared relative risks (RR) for fatigue, memory disturbance, or shortness of breath among exposed and unexposed using Poisson regression models, assessing sex, age, education, country of origin, and pre-pandemic presence of the same symptom and comorbidity as possible risk factors, with additional analyses to assess hospitalisation for COVID-19 as a risk factor among exposed.

RESULTS

The exposed group (N = 53 846) had a higher prevalence of most outcome symptoms compared to the unexposed (N = 485 757), with the highest risk for shortness of breath (HR 2.75; 95%CI 2.59-2.93), fatigue (2.08; 2.00-2.16) and memory disturbance (1.41;1.26-1.59). High HRs were also found for disturbance of smell/taste and hair loss, but frequencies were low. Concerning risk factors, sociodemographic factors were at large similarly associated with outcome symptoms in both groups. Registration of the outcome symptom before the pandemic increased the risk for fatigue, memory disturbance and shortness of breath after COVID-19, but these associations were weaker among exposed. Comorbidity was not associated with fatigue and shortness of breath in the COVID-19 group. For memory disturbance, the RR was slightly increased with the higher comorbidity score both among exposed and unexposed.

CONCLUSION

COVID-19 was associated with a range of symptoms lasting more than three months after the infection.

Reproductive outcomes in women and men conceived by assisted reproductive technologies in Norway: prospective registry based study

Objectives

To determine whether the perinatal outcomes of women or men who were conceived by assisted reproductive technologies are different compared with their peers who were naturally conceived.

Design

Prospective registry based study.

Setting

Medical Birth Registry of Norway.

Participants

People born in Norway between 1984 and 2002 with a registered pregnancy by the end of 2021.

Exposure

People who were conceived by assisted reproductive technologies and have had a registered pregnancy.

Main outcome measures

Comparing pregnancies and births of people who were conceived by assisted reproductive technologies and people who were naturally conceived, we assessed mean birth weight, gestational age, and placental weight by linear regression, additionally, the odds of congenital malformations, a low 5 min Apgar score (<7), transfer to a neonatal intensive care unit, delivery by caesarean section, use of assisted reproductive technologies, hypertensive disorders of pregnancy and pre-eclampsia, preterm birth, and offspring sex, by logistic regression. The occurrence of any registered pregnancy from people aged 14 years until age at the end of follow-up was assessed using Cox proportional regression for both groups.

Results

Among 1 092 151 people born in Norway from 1984 to 2002, 180 652 were registered at least once as mothers, and 137 530 as fathers. Of these, 399 men and 553 women were conceived by assisted reproductive technologies. People who were conceived by assisted reproductive technologies had little evidence of increased risk of adverse outcomes in their own pregnancies, increased use of assisted reproductive technologies, or any difference in mean birth weight, placental weight, or gestational age. The only exception was for an increased risk of the neonate having a low Apgar score at 5 min (adjusted odds ratio 1.86 (95% confidence interval 1.20 to 2.89)) among women who were conceived by assisted reproductive technologies. Odds were slightly decreased of having a boy among mothers conceived by assisted reproductive technologies (odds ratio 0.79 (95% confidence interval 0.67 to 0.93)). People conceived by assisted reproductive technologies were slightly less likely to have a registered pregnancy within the follow-up period (women, adjusted hazard ratio 0.88 (95% CI 0.81 to 0.96); men, 0.91 (0.83 to 1.01)).

Conclusions

People conceived by assisted reproductive technologies were not at increased risk of obstetric or perinatal complications when becoming parents. The proportion of people conceived by assisted reproductive technologies with a registered pregnancy was lower than among people who were naturally conceived, but a longer follow-up is required to fully assess their fertility and reproductive history.

Impact of COVID-19 on pregnancy-related healthcare utilisation: a prospective nationwide registry study

OBJECTIVE

To assess the impact of COVID-19 on pregnancy-related healthcare utilisation and differences across social groups.

DESIGN

Nationwide longitudinal prospective registry-based study.

SETTING

Norway.

PARTICIPANTS

Female residents aged 15-50 years (n=1 244 560).

MAIN OUTCOME MEASURES

Pregnancy-related inpatient, outpatient and primary care healthcare utilisation before the COVID-19 pandemic (prepandemic: 1 January to 11 March 2020), during the initial lockdown (first wave: 12 March to 3 April 2020), during the summer months of low restrictions (summer period: 4 April to 31 August 2020) and during the second wave to the end of the year (second wave: 1 September to 31 December 2020). Rates were compared with the same time periods in 2019.

RESULTS

There were 130 924 inpatient specialist care admissions, 266 015 outpatient specialist care consultations and 2 309 047 primary care consultations with pregnancy-related diagnostic codes during 2019 and 2020. After adjusting for time trends and cofactors, inpatient admissions were reduced by 9% (adjusted incidence rate ratio (aIRR)=0.91, 95% CI 0.87 to 0.95), outpatient consultations by 17% (aIRR=0.83, 95% CI 0.71 to 0.86) and primary care consultations by 10% (aIRR=0.90, 95% CI 0.89 to 0.91) during the first wave. Inpatient care remained 3%-4% below prepandemic levels throughout 2020. Reductions according to education, income and immigrant background were also observed. Notably, women born in Asia, Africa or Latin America had a greater reduction in inpatient (aIRR=0.87, 95% CI 0.77 to 0.97) and outpatient (aIRR 0.90, 95% CI 0.86 to 0.95) care during the first wave, compared with Norwegian-born women. We also observed that women with low education had a greater reduction in inpatient care during summer period (aIRR=0.88, 95% CI 0.83 to 0.92), compared with women with high educational attainment.

CONCLUSION

Following the introduction of COVID-19 mitigation measures in Norway in March 2020, there were substantial reductions in pregnancy-related healthcare utilisation, especially during the initial lockdown and among women with an immigrant background.

Investigating causal relations between sleep duration and risks of adverse pregnancy and perinatal outcomes: linear and nonlinear Mendelian randomization analyses

BACKGROUND

Observational studies have reported maternal short/long sleep duration to be associated with adverse pregnancy and perinatal outcomes. However, it remains unclear whether there are nonlinear causal effects. Our aim was to use Mendelian randomization (MR) and multivariable regression to examine nonlinear effects of sleep duration on stillbirth (MR only), miscarriage (MR only), gestational diabetes, hypertensive disorders of pregnancy, perinatal depression, preterm birth and low/high offspring birthweight.

METHODS

We used data from European women in UK Biobank (N=176,897), FinnGen (N=~123,579), Avon Longitudinal Study of Parents and Children (N=6826), Born in Bradford (N=2940) and Norwegian Mother, Father and Child Cohort Study (MoBa, N=14,584). We used 78 previously identified genetic variants as instruments for sleep duration and investigated its effects using two-sample, and one-sample nonlinear (UK Biobank only), MR. We compared MR findings with multivariable regression in MoBa (N=76,669), where maternal sleep duration was measured at 30 weeks.

RESULTS

In UK Biobank, MR provided evidence of nonlinear effects of sleep duration on stillbirth, perinatal depression and low offspring birthweight. Shorter and longer duration increased stillbirth and low offspring birthweight; shorter duration increased perinatal depression. For example, longer sleep duration was related to lower risk of low offspring birthweight (odds ratio 0.79 per 1 h/day (95% confidence interval: 0.67, 0.93)) in the shortest duration group and higher risk (odds ratio 1.40 (95% confidence interval: 1.06, 1.84)) in the longest duration group, suggesting shorter and longer duration increased the risk. These were supported by the lack of evidence of a linear effect of sleep duration on any outcome using two-sample MR. In multivariable regression, risks of all outcomes were higher in the women reporting <5 and ≥10 h/day sleep compared with the reference category of 8-9 h/day, despite some wide confidence intervals. Nonlinear models fitted the data better than linear models for most outcomes (likelihood ratio P-value=0.02 to 3.2×10-52), except for gestational diabetes.

CONCLUSIONS

Our results show shorter and longer sleep duration potentially causing higher risks of stillbirth, perinatal depression and low offspring birthweight. Larger studies with more cases are needed to detect potential nonlinear effects on hypertensive disorders of pregnancy, preterm birth and high offspring birthweight.

General practitioner visits after SARS-CoV-2 omicron compared with the delta variant in children in Norway: a prospective nationwide registry study

BACKGROUND

SARS-CoV-2 infection in children is followed by an immediate increase in primary care utilisation. The difference in utilisation following infection with the delta and omicron virus variants is unknown.

OBJECTIVES

To study whether general practitioner (GP) contacts were different in children infected with the omicron versus delta variant for up to 4 weeks after the week testing positive.

SETTING

Primary care.

PARTICIPANTS

All residents in Norway aged 0-10. After excluding 47 683 children with a positive test where the virus variant was not identified as delta or omicron and 474 children who were vaccinated, the primary study population consisted of 613 448 children.

MAIN OUTCOME MEASURES

GP visits.

METHODS

We estimated the difference in the weekly share visiting the GP after being infected with the delta or omicron variant to those in the study population who were either not tested or who tested negative using an event study design, controlling for calendar week of consultation, municipality fixed effects and sociodemographic factors in multivariate logistic regressions.

RESULTS

Compared with preinfection, increased GP utilisation was found for children 1 and 2 weeks after testing positive for the omicron variant, with an OR of 6.7 (SE: 0.69) in the first week and 5.5 (0.72) in the second week. This increase was more pronounced for children with the delta variant, with an OR of 8.2 (0.52) in the first week and 7.1 (0.93) in the second week. After 2 weeks, the GP utilisation returned to preinfection levels.

CONCLUSION

The omicron variant appears to have resulted in less primary healthcare interactions per infected child compared with the delta variant.

Early childhood respiratory tract infections according to parental subfertility and conception by assisted reproductive technologies

STUDY QUESTION

Are children conceived by ART or born to subfertile parents more susceptible to upper or lower respiratory tract infections (URTI, LRTI)?

SUMMARY ANSWER

ART-conceived children had a higher frequency of and risk of hospitalization for respiratory infections up to age 3, which was only partly explained by parental subfertility.

WHAT IS KNOWN ALREADY

Some studies report increased risks of infections in children conceived by ART. Results for URTIs and LRTIs are inconclusive, and the contribution of underlying parental subfertility remains unclear.

STUDY DESIGN, SIZE, DURATION

We included 84 102 singletons of the Norwegian Mother, Father and Child Cohort Study (MoBa) born between 1999 and 2009. Mothers reported time-to-pregnancy at recruitment and child history of, frequency of and hospitalization for, respiratory infections when the child was 6, 18 and 36 months old by questionnaires. Subfertility was defined as having taken 12 or more months to conceive. The Medical Birth Registry of Norway (MBRN) provided information on ART. URTI included throat and ear infections, while LRTI included bronchitis, bronchiolitis, respiratory syncytial virus and pneumonia.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We used log-binomial regression to estimate risk ratios (RR) and 95% CI of any respiratory tract infection and hospitalization, and negative-binomial regression to calculate incidence rate ratios (IRR) and 95% CI for number of infections. We compared children conceived by ART, and naturally conceived children of subfertile parents, to children of fertile parents (<12 months to conceive) while adjusting for maternal age, education, BMI and smoking during pregnancy and previous livebirths. We accounted for dependency between children born to the same mother.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 7334 (8.7%) singletons were naturally conceived by subfertile parents and 1901 (2.3%) were conceived by ART. Between age 0 and 36 months, 41 609 (49.5%) of children experienced any URTI, 15 542 (18.5%) any LRTI and 4134 (4.9%) were hospitalized due to LRTI. Up to age 3, children conceived by ART had higher frequencies of URTI (adjusted IRR (aIRR) 1.16; 95% CI 1.05–1.28) and hospitalizations due to LRTI (adjusted RR (aRR) 1.25; 95% CI 1.02–1.53), which was not seen for children of subfertile parents. Children conceived by ART were not at higher risks of respiratory infections up to age 18 months; only at age 19–36 months, they had increased risk of any LRTI (aRR 1.16; 95% CI 1.01–1.33), increased frequency of LRTIs (IRR 1.22; 95% CI 1.02–1.47) and a higher risk of hospitalization for LRTI (aRR 1.35; 95% CI 1.01–1.80). They also had an increased frequency of URTIs (aIRR; 1.19; 95% CI 1.07–1.33). Children of subfertile parents only had a higher risk of LRTIs (aRR 1.09; 95% CI 1.01–1.17) at age 19–36 months.

LIMITATIONS, REASONS FOR CAUTION

Self-reported time-to-pregnancy and respiratory tract infections by parents could lead to misclassification. Both the initial participation rate and loss to follow up in the MoBa limits generalizability to the general Norwegian population.

WIDER IMPLICATIONS OF THE FINDINGS

ART-conceived children might be more susceptible to respiratory tract infections in early childhood. This appears to be only partly explained by underlying parental subfertility. Exactly what aspects related to the ART procedure might be reflected in these associations need to be further investigated.

STUDY FUNDING/COMPETING INTEREST(S)

Funding was received from the Swiss National Science Foundation (P2BEP3_191798), the Research Council of Norway (no. 262700), and the European Research Council (no. 947684). All authors declare no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

Health at age 17 in Norwegian adolescents: Mental and physical status in the national cohort born in 2001

AIMS

We present self-reported data on physical and mental health at age 17 years from 82% of Norwegians born in 2001.

METHODS

In Norway, the Armed Forces require that each resident who reaches the age of 17 years completes a self-administered declaration of health that is used for military selection. The declaration collects information on height and weight, various clinically diagnosed diseases, mental and behavioural disorders, and other health conditions where clinical diagnosis is not required. In 2018, there were 65,913 adolescents born in 2001 living in Norway, of whom 10,223 were exempt from completing the declaration; declarations were therefore sent to 55,690 participants. We included 54,132 participants who completed the declaration (response rate 97.2%): 27,220 male and 26,912 female respondents.

RESULTS

We found that 18% of male and 28% of female respondents reported at least one clinically diagnosed disease, mental disorder or behavioural disorder. Among health condition where clinical diagnosis was not required, 19% of male and 37% of female respondents reported anxiety/depression affecting daily life and 10 versus 18% reported migraines/recurring headaches. The respondents probably represent the healthiest part of the total cohort of 17-year-old Norwegians because those who are exempt from completing the declaration are already considered unfit for military service.

CONCLUSIONS

These data represent a rich resource for further research. Similar data exist for the birth cohorts in 1993-2003. We encourage further research that can help decision-makers identify areas of concern that should be targeted for interventions.

Antipsychotic use in pregnancy and risk of attention/deficit-hyperactivity disorder and autism spectrum disorder: a Nordic cohort study

Background

Antipsychotics are increasingly used among women of childbearing age and during pregnancy.

Objective

To determine whether children exposed to antipsychotics in utero are at increased risk of attention-deficit/hyperactivity disorder (ADHD) or autism spectrum disorder (ASD), accounting for maternal diagnoses of bipolar, psychotic and other psychiatric disorders.

Design

Population-based cohort study, including a sibling analysis.

Setting

Nationwide data on all pregnant women and their live-born singletons in Denmark (1997-2017), Finland (1996-2016), Iceland (2004-2017), Norway (2004-2017), and Sweden (2006-2016).

Participants

4 324 086 children were eligible for inclusion to the study cohort.

Intervention

Antipsychotic exposure in utero, assessed by pregnancy trimester, type of antipsychotic, and varying patterns of use.

Main outcome measures

Non-mutually exclusive diagnoses of ADHD and ASD. We used Cox proportional hazard models to calculate hazard ratios (HRs) controlling for maternal psychiatric disorders and other potential confounding factors.

Findings

Among 4 324 086 singleton births, 15 466 (0.4%) were exposed to antipsychotics in utero. During a median follow-up of 10 years, we identified 72 257 children with ADHD and 38 674 children with ASD. Unadjusted HRs were raised for both outcomes but shifted substantially towards the null after adjustment; 1.10 (95%CI 1.00 to 1.27) for ADHD and 1.12 (0.97 to 1.29) for ASD. Adjusted HRs remained consistent by trimester of exposure and type of antipsychotic. Comparing in utero exposure with pre-pregnancy use yielded HRs of 0.74 (0.62 to 0.87) for ADHD and 0.88 (0.70 to 1.10) for ASD. Sibling analyses yielded HRs of 1.14 (0.79 to 1.64) for ADHD and 1.34 (0.75 to 2.39) for ASD.

Discussion

Our findings suggest little or no increased risk of child ADHD or ASD after in utero exposure to antipsychotics.

Clinical implications

Results regarding child neurodevelopment are reassuring for women who need antipsychotics during pregnancy.

Social and life skills in adolescents who have self-harmed: analysis of survey responses from a national sample of adolescents in Norway

OBJECTIVE

Social and life skills (SLS) may be important in the prevention and treatment of self-harm, but few studies have described this relationship. We examined three components of SLS in adolescents who reported self-harm that was, according to themselves, diagnosed by a clinician.

DESIGN

Cross-sectional.

SETTING

National screening prior to military service.

PARTICIPANTS

176 284 residents of Norway born in 1999-2001 received a declaration of health. We included 171 486 individuals (84 153 (49%) women and 87 333 (51%) men) who were 17 (n=1 67 855) or 18 years of age (n=3631) when they completed the declaration.

OUTCOME MEASURE

The main outcome was clinically diagnosed self-harm, defined as self-harm that the adolescents themselves stated had been diagnosed by a clinician. Components of SLS were social interactions; coping strategies; and emotional regulation/aggression. The association between SLS and self-reported clinically diagnosed self-harm was assessed in hierarchical multiple regression models controlling for sex; school absence; and feelings of emotional pain.

RESULTS

Three percent (n=5507) of the adolescents reported clinically diagnosed self-harm. The three components of SLS together added little to the prediction of clinically diagnosed self-harm (∆R²=0.02). After controlling for school absence and emotional pain, emotional regulation/aggression was the only SLS-component that was independently associated with clinically diagnosed self-harm (OR 1.33, 95% CI 1.31 to 1.36). The young men who said they had been clinically diagnosed for self-harm scored slightly worse on social interactions (Hedge's g (g) = -0.13, p<0.001) and emotional regulation/aggression (g = -0.18, p<0.001) than the young women in this group.

CONCLUSION

Young women and young men who reported clinically diagnosed self-harm had more problems with emotional regulation/aggression than other adolescents, but did not have worse social interactions or coping strategies.

Pregnancy and risk of COVID-19: a Norwegian registry-linkage study

Objective

To compare the risk of acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection and contact with specialist healthcare services for coronavirus disease 2019 (COVID‐19) between pregnant and non‐pregnant women.

Population or sample

All women ages 15–45 living in Norway on 1 March 2020 (n = 1 033 699).

Methods

We linked information from the national birth, patient, communicable diseases and education databases using unique national identifiers.

Main outcome measure

We estimated hazard ratios (HR) among pregnant compared to non‐pregnant women of having a positive test for SARS‐CoV‐2, a diagnosis of COVID‐19 in specialist healthcare, or hospitalisation with COVID‐19 using Cox regression. Multivariable analyses adjusted for age, marital status, education, income, country of birth and underlying medical conditions.

Results

Pregnant women were not more likely to be tested for or to a have a positive SARS‐CoV‐2 test (adjusted HR 0.99; 95% CI 0.92–1.07). Pregnant women had higher risk of hospitalisation with COVID‐19 (HR 4.70, 95% CI 3.51–6.30) and any type of specialist care for COVID‐19 (HR 3.46, 95% CI 2.89–4.14). Pregnant women born outside Scandinavia were less likely to be tested, and at higher risk of a positive test (HR 2.37, 95% CI 2.51–8.87). Compared with pregnant Scandinavian‐born women, pregnant women with minority background had a higher risk of hospitalisation with COVID‐19 (HR 4.72, 95% CI 2.51–8.87).

Conclusion

Pregnant women were not more likely to be infected with SARS‐CoV‐2. Still, pregnant women with COVID‐19, especially those born outside of Scandinavia, were more likely to be hospitalised.

Tweetable abstract

Pregnant women are at increased risk of hospitalisation for COVID‐19.

Pregnant women are at increased risk of hospitalisation for COVID‐19.

Yersinia enterocolitica: A Follow-up of the Outbreak in the Norwegian Armed Forces in 2014

INTRODUCTION

In the spring of 2014, there was an outbreak of Yersinia enterocolitica (YE) gastroenteritis in four Norwegian military camps-the largest outbreak ever reported in Norway. YE is usually transmitted via food, and the gastrointestinal disease caused by the bacterium is considered a public health problem in several countries. Common symptoms of YE gastroenteritis are abdominal pain, diarrhea, fever, nausea, and vomiting. Post-infectious complications can occur after YE gastroenteritis, the most common of which are erythema nodosum and reactive arthritis. Based on self-reported data, we describe the duration of illness, the duration of any absence from service, and the incidence of symptoms of post-infectious complications in two groups of servicepeople: one diagnosed with YE gastroenteritis and the other with an unspecified acute infectious gastroenteritis.

MATERIALS AND METHODS

The Norwegian Armed Forces Health Register (NAFHR) is a central health register that contains data from conscripts and from military and civilian personnel in the Norwegian Armed Forces. In this study, we identified all individuals with a diagnosis of YE gastroenteritis in the NAFHR in the period from January 1 to June 30, 2014 (n = 128) as well as all those with a diagnosis of an unspecified acute infectious gastroenteritis in the same period (n = 323) to participate as controls. In October 2018, a link to an internet-based questionnaire was distributed by e-mail to all identified individuals. The questionnaires collected data on the duration of illness, the duration of absence from service, and the incidence of symptoms of post-infectious complications.

RESULTS

Of all those who received the questionnaire, 72 (59%) were included in the YE group and 117 people (36%) were included in the control group. Half of those in the YE group were ill for more than 13 days, while almost all (90%) of those in the control group recovered after 1 week. There were no differences between the groups in the incidence of symptoms of post-infectious complications during the 6 weeks after recovery. There was a significantly larger proportion of officers than conscripts in the YE group who reported symptoms of post-infectious complications. None of the respondents reported symptoms of post-infectious complications in the 6 months after the termination of military service.

CONCLUSION

One strength of this study is that we were able to investigate a large outbreak of YE gastroenteritis in a group of individuals with good underlying health. Weaknesses are the low response rate, especially in the control group, and the fact that we sent out the questionnaire >4 years after the acute gastroenteritis occurred. YE gastroenteritis among personnel in the Norwegian Armed Forces was associated with a significantly longer duration of illness and a longer duration of absence from service than that resulting from an unspecified acute infectious gastroenteritis. However, YE gastroenteritis was not associated with more symptoms of post-infectious complications.

Associations between interpregnancy interval and preterm birth by previous preterm birth status in four high-income countries: a cohort study

OBJECTIVE

To investigate the effect of interpregnancy interval (IPI) on preterm birth (PTB) according to whether the previous birth was preterm or term.

DESIGN

Cohort study.

SETTING

USA (California), Australia, Finland, Norway (1980-2017).

POPULATION

Women who gave birth to first and second (n = 3 213 855) singleton livebirths.

METHODS

Odds ratios (ORs) for PTB according to IPIs were modelled using logistic regression with prognostic score stratification for potential confounders. Within-site ORs were pooled by random effects meta-analysis.

OUTCOME MEASURE

PTB (gestational age <37 weeks).

RESULTS

Absolute risk of PTB for each IPI was 3-6% after a previous term birth and 17-22% after previous PTB. ORs for PTB differed between previous term and preterm births in all countries (P-for-interaction ≤ 0.001). For women with a previous term birth, pooled ORs were increased for IPI <6 months (OR 1.50, 95% CI 1.43-1.58); 6-11 months (OR 1.10, 95% CI 1.04-1.16); 24-59 months (OR 1.16, 95% CI 1.13-1.18); and ≥ 60 months (OR 1.72, 95%CI 1.60-1.86), compared with 18-23 months. For previous PTB, ORs were increased for <6 months (OR 1.30, 95% CI 1.18-1.42) and ≥60 months (OR 1.29, 95% CI 1.17-1.42), but were less than ORs among women with a previous term birth (P < 0.05).

CONCLUSIONS

Associations between IPI and PTB are modified by whether or not the previous pregnancy was preterm. ORs for short and long IPIs were higher among women with a previous term birth than a previous PTB, which for short IPI is consistent with the maternal depletion hypothesis. Given the high risk of recurrence and assuming a causal association between IPI and PTB, IPI remains a potentially modifiable risk factor for women with previous PTB.

TWEETABLE ABSTRACT

Short versus long interpregnancy intervals associated with higher ORs for preterm birth (PTB) after a previous PTB.

Severe acute respiratory syndrome coronavirus 2 prevalence in 1170 asymptomatic Norwegian conscripts

BACKGROUND

Accurate estimates of SARS-CoV-2 infection in different population groups are important for the health authorities. In Norway, public infection control measures have successfully curbed the pandemic. However, military training and service are incompatible with these measures; therefore extended infection control measures were implemented in the Norwegian Armed Forces. We aimed to describe these measures, discuss their value, and investigate the polymerase chain reaction (PCR) prevalence and seroprevalence of SARS-CoV-2, as well as changes in antibody titer levels over the 6-week military training period in a young, asymptomatic population of conscripts.

METHODS

In April 2020, 1170 healthy conscripts (median age 20 years) enrolled in military training. Extended infection control measures included a pre-enrollment telephone interview, self-imposed quarantine, questionnaires, and serial SARS-CoV-2 testing. At enrollment, questionnaires were used to collect information on symptoms, and SARS-CoV-2 rapid antibody testing was conducted. Serial SARS-CoV-2 PCR and serology testing were used to estimate the prevalence of confirmed SARS-CoV-2 and monitor titer levels at enrollment, and 3 and 6 weeks thereafter.

RESULTS

At enrollment, only 0.2% of conscripts were SARS-CoV-2 PCR-positive, and seroprevalence was 0.6%. Serological titer levels increased nearly 5-fold over the 6-week observation period. Eighteen conscripts reported mild respiratory symptoms during the 2 weeks prior to enrollment (all were PCR-negative; one was serology-positive), whereas 17 conscripts reported respiratory symptoms and nine had fever at enrollment (all were PCR- and serology-negative).

CONCLUSIONS

The prevalence of SARS-CoV-2 was less than 1% in our sample of healthy Norwegian conscripts. Testing of asymptomatic conscripts seems of no value in times of low COVID-19 prevalence. SARS-CoV-2 antibody titer levels increased substantially over time in conscripts with mild symptoms.

The international Perinatal Outcomes in the Pandemic (iPOP) study: protocol

Preterm birth is the leading cause of infant death worldwide, but the causes of preterm birth are largely unknown. During the early COVID-19 lockdowns, dramatic reductions in preterm birth were reported; however, these trends may be offset by increases in stillbirth rates. It is important to study these trends globally as the pandemic continues, and to understand the underlying cause(s). Lockdowns have dramatically impacted maternal workload, access to healthcare, hygiene practices, and air pollution - all of which could impact perinatal outcomes and might affect pregnant women differently in different regions of the world.

In the international Perinatal Outcomes in the Pandemic (iPOP) Study, we will seize the unique opportunity offered by the COVID-19 pandemic to answer urgent questions about perinatal health. In the first two study phases, we will use population-based aggregate data and standardized outcome definitions to: 1) Determine rates of preterm birth, low birth weight, and stillbirth and describe changes during lockdowns; and assess if these changes are consistent globally, or differ by region and income setting, 2) Determine if the magnitude of changes in adverse perinatal outcomes during lockdown are modified by regional differences in COVID-19 infection rates, lockdown stringency, adherence to lockdown measures, air quality, or other social and economic markers, obtained from publicly available datasets. We will undertake an interrupted time series analysis covering births from January 2015 through July 2020.

The iPOP Study will involve at least 121 researchers in 37 countries, including obstetricians, neonatologists, epidemiologists, public health researchers, environmental scientists, and policymakers. We will leverage the most disruptive and widespread “natural experiment” of our lifetime to make rapid discoveries about preterm birth. Whether the COVID-19 pandemic is worsening or unexpectedly improving perinatal outcomes, our research will provide critical new information to shape prenatal care strategies throughout (and well beyond) the pandemic.

Influenza vaccination and risk for cardiovascular events: a nationwide self-controlled case series study

Background

US and European guidelines diverge on whether to vaccinate adults who are not at high risk for cardiovascular events against influenza. Here, we investigated the associations between influenza vaccination and risk for acute myocardial infarction, stroke and pulmonary embolism during the 2009 pandemic in Norway, when vaccination was recommended to all adults.

Methods

Using national registers, we studied all vaccinated Norwegian individuals who suffered AMI, stroke, or pulmonary embolism from May 1, 2009 through September 30, 2010. We defined higher-risk individuals as those using anti-diabetic, anti-obesity, anti-thrombotic, pulmonary or cardiovascular medications (i.e. individuals to whom vaccination was routinely recommended); all other individuals were regarded as having lower-risk. We estimated incidence rate ratios with 95% CI using conditional Poisson regression in the pre-defined risk periods up to 180 days following vaccination compared to an unexposed time-period, with adjustment for season or daily temperature.

Results

Overall, we observed lower risk for cardiovascular events following influenza vaccination. When stratified by baseline risk, we observed lower risk across all three outcomes in association with vaccination among higher-risk individuals. In this subgroup, relative risks were 0.72 (0.59–0.88) for AMI, 0.77 (0.59–0.99) for stroke, and 0.73 (0.45–1.19) for pulmonary embolism in the period 1–14 days following vaccination when compared to the background period. These associations remained essentially the same up to 180 days after vaccination. In contrast, the corresponding relative risks among subjects not using medications were 4.19 (2.69–6.52), 1.73 (0.91–3.31) and 2.35 (0.78–7.06).

Conclusion

In this nationwide study, influenza vaccination was associated with overall cardiovascular benefit. This benefit was concentrated among those at higher cardiovascular risk as defined by medication use. In contrast, our results demonstrate no comparable inverse association with thrombosis-related cardiovascular events following vaccination among those free of cardiovascular medications at baseline. These results may inform the risk–benefit balance for universal influenza vaccination.

Deaths after confirmed SARS-CoV-2 in Norway

BACKGROUND

Advanced age is the most important risk factor for death as a result of COVID-19, but there is a dearth of knowledge regarding the impact of chronic diseases. Using health registry data, we describe the disease profiles of persons who died after a confirmed infection with SARS-CoV-2 during the first three months of the pandemic in Norway.

MATERIAL AND METHOD

Data from the specialist health service (Norwegian Patient Registry, NPR) and the primary health service (Norwegian Registry for Primary Health Care, NRPHC) were linked to information on positive tests for SARS-CoV-2 from the Norwegian Surveillance System for Communicable Diseases (MSIS) and on deaths from the National Population Register. The data retrieval included the Norwegian population as of 1 March 2020 with data for confirmed infections, hospitalisations and deaths until 31 May 2020.

RESULTS

Of 8 412 persons with a confirmed SARS-CoV-2 infection, altogether 244 (2.9 %) died, whereof 133 (55 %) were men. Among those with a confirmed infection, the proportion who died varied from 0.2 % (age < 60 years) to 52 % (age ≥ 90 years). Altogether 92 (38 %) patients died in hospital. 25 (16 %) of those who died elsewhere had previously been hospitalised for COVID-19. The proportion with no registered chronic disease was 39 % in the age group < 70 years and 26 % in the age group ≥ 70 years. The disease distribution varied between those patients who had died in and outside of hospital, especially for diagnoses of diabetes, renal failure and dementia.

INTERPRETATION

Among those who had a SARS-CoV-2 infection confirmed during the first three months of the pandemic in Norway, only a small proportion died. The majority of those who died were 70 years or older and had at least one chronic disease, but the disease profile varied between patients who died in and outside of hospital. Health registry data can help provide a better overview of and advice to risk groups in the population during an ongoing pandemic.

Risk conditions in children hospitalized with influenza in Norway, 2017-2019

BACKGROUND

Norwegian children are more frequently hospitalized with influenza than adults. Little is known about the characteristics of these children. Our aim was to investigate the presence of pre-existing risk conditions and to determine the duration of influenza hospitalizations in children during two influenza seasons.

METHODS

The Norwegian Patient Registry holds data on all hospitalized patients in Norway. We included all patients younger than 18 years hospitalized with a diagnosis of influenza during the influenza seasons 2017-18 and 2018-19. Pre-existing risk conditions for influenza were identified by ICD-10 diagnoses in the Norwegian Patient Registry. In addition, information on asthma diagnoses were also retrieved from the Norwegian Registry for Primary Health Care. To estimate the prevalence of risk conditions in the child population, we obtained diagnoses on all Norwegian children in a two-year period prior to each influenza season. We calculated age-specific rates for hospitalization and risk for being hospitalized with influenza in children with risk conditions.

RESULTS

In total, 1013 children were hospitalized with influenza during the two influenza seasons. Children younger than 6 months had the highest rate of hospitalization, accounting for 13.5% of all admissions (137 children). Hospitalization rates decreased with increasing age. Among children hospitalized with influenza, 25% had one or more pre-existing risk conditions for severe influenza, compared to 5% in the general population under 18 years. Having one or more risk conditions significantly increased the risk of hospitalization, (Odds Ratio (OR) 6.1, 95% confidence interval (CI) 5.0-7.4 in the 2017-18 season, and OR 6.8, 95% CI 5.4-8.4 in the 2018-19 season). Immunocompromised children and children with epilepsy had the highest risk of hospitalization with influenza, followed by children with heart disease and lung disease. The average length of stay in hospital were 4.6 days, and this did not differ with age.

CONCLUSION

Children with pre-existing risk conditions for influenza had a higher risk of hospitalization for influenza. However, most children (75%) admitted to hospital with influenza in Norway during 2017-2019 did not have pre-existing risk conditions. Influenza vaccination should be promoted in particular for children with risk conditions and pregnant women to protect new-borns.

The demographics of assisted reproductive technology births in a Nordic country

STUDY QUESTION

What are the socio-demographic characteristics of families in Norway who have children after assisted reproductive technology (ART), and have these characteristics changed over time?

SUMMARY ANSWER

Parents who conceive through ART in Norway tend to be advantaged families, and their socio-demographic profile has not changed considerably over the period 1985-2014.

WHAT IS KNOWN ALREADY

A small number of studies show that couples who conceive through ART tend to be socio-economically advantaged.

STUDY DESIGN, SIZE, DURATION

Norwegian Population Register, the Medical Birth Register and the national data bases were linked to study all live births in Norway between 1985 and 2014.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The sample consisted of 1 757 768 live births. Simple bivariate analyses were performed to describe the socio-demographic characteristics of parents who conceived through ART and changes in these characteristics over the time period 1985-2014. We used linear probability models to estimate the association between parental income and giving birth after ART from 2000 to 2014, before and after adjustment for maternal age at delivery, education and area of residence.

MAIN RESULTS AND THE ROLE OF CHANCE

Parents conceiving through ART were more likely to be older, with the highest levels of income and education, and married. Their socio-demographic profiles did not change considerably during the period 1985-2014. In the unadjusted model, parents belonging to the top income quartile were 4.2 percentage points more likely (95% CI: 4.1 to 4.3) to have conceived through ART than parents who belonged to the bottom income quartile. Adjustment for maternal age only partially reduced the income disparities (for the top income quartile by 35% (β = 2.7 with 95% CI: 2.5 to 2.8)). Additional adjustment for maternal education, marital status and area of residence did not further attenuate the associations.

LIMITATIONS, REASONS FOR CAUTION

The data does not enable us to tell whether the lower numbers of children conceived through ART amongst more disadvantaged individuals is caused by lower success rates with ART treatment, lower demand of ART services or barriers faced in access to ART. The study focuses on Norway, a context characterised by high subsidisation of ART services.

WIDER IMPLICATIONS OF THE FINDINGS

Even though in Norway access to ART services is highly subsidised, the results highlight important and persisting social inequities in use of ART. The results also indicate that children born after ART grow up in resourceful environments, which will benefit their development and well-being.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by European Research Council agreement n. 803959 (to A.G.), by Economic and Social Research Council grant ES/M001660/1 and by the Research Council of Norway through its Centres of Excellence funding scheme, project number 262700. The authors have no conflict of interest to declare.

TRIAL REGISTRATION NUMBER

Not applicable.

Probability and outcomes of second pregnancy after HELLP syndrome in the first: A population-based registry study

INTRODUCTION

Some studies have suggested that women may avoid further pregnancies after experiencing a pregnancy affected by a hypertensive disorder. Large population-based studies are needed to better understand the outcomes of later pregnancies among women who have a history of hypertensive disorders of pregnancy. The aims of the study were to assess outcomes of the second pregnancy and second delivery rate among women experiencing Hemolysis, elevated liver enzymes and low platelet count (HELLP) syndrome in their first pregnancy.

MATERIAL AND METHODS

This population-based registry study included all women with a first delivery registered in the Medical Birth Registry of Norway from 1999 to 2014 (n = 418 897). Logistic regression was used to estimate odds ratios (ORs) with 95% confidence intervals (CIs) for adverse outcomes of the second delivery and the probability of no second delivery among women with HELLP syndrome in first pregnancy compared with women without HELLP syndrome. We also compared outcomes in the first and second pregnancies among women with HELLP syndrome in first.

RESULTS

HELLP syndrome occurred in 0.24% of first pregnancies (n = 1006). Among women with HELLP syndrome in their first pregnancy, adverse outcomes were substantially less frequent in the second pregnancy: preterm deliveries declined from 56.0% to 14.2%, and small for gestational age from 6.6% to 2.8%. More than 75% had no hypertensive disorder in their second pregnancy. Still, compared with women without a history of HELLP syndrome, ORs for adverse outcomes in second pregnancies were increased: preterm birth (OR 3.7, 95% CI 2.8-4.8), small for gestational age (OR 2.7, 95% CI 1.6-4.8), perinatal death (OR 3.1, 95% CI 1.4-7.0), placental abruption (OR 4.2, 95% CI 1.8-9.4) and hypertensive complication (OR 8.3, 95% CI 6.7-10.3). HELLP syndrome did not influence the probability of a second delivery.

CONCLUSIONS

Among women with HELLP syndrome in their first pregnancy, the occurrence of adverse pregnancy outcomes was substantially reduced in the second pregnancy. However, compared with unaffected women, they were still at greater risk of pregnancy complications.

Seasonal and pandemic influenza during pregnancy and risk of fetal death: A Norwegian registry-based cohort study

Previous studies of fetal death with maternal influenza have been inconsistent. We explored the effect of maternal influenza-like illness (ILI) in pregnancy on the risk of fetal death, distinguishing between diagnoses during regular influenza seasons and the 2009/2010 pandemic and between trimesters of ILI. We used birth records from the Medical Birth Registry of Norway to identify fetal deaths after the first trimester in singleton pregnancies (2006-2013). The Norwegian Directorate of Health provided dates of clinical influenza diagnoses by primary-health-care providers, whereas dates of laboratory-confirmed influenza A (H1N1) diagnoses were provided by the Norwegian Surveillance System for Communicable Diseases. We obtained dates and types of influenza vaccinations from the Norwegian Immunisation Registry. Cox proportional-hazards regression models were fitted to estimate hazard ratios (HRs) of fetal death, with associated 95% confidence intervals (CIs), comparing women with and without an ILI diagnosis in pregnancy. There were 2510 fetal deaths among 417,406 eligible pregnancies. ILI during regular seasons was not associated with increased risk of fetal death: adjusted HR = 0.90 (95% CI 0.64-1.27). In contrast, ILI during the pandemic was associated with substantially increased risk of fetal death, with an adjusted HR of 1.75 (95% CI 1.21-2.54). The risk was highest following first-trimester ILI (adjusted HR = 2.28 [95% CI 1.45-3.59]). ILI during the pandemic-but not during regular seasons-was associated with increased risk of fetal death in the second and third trimester. The estimated effect was strongest with ILI in first trimester.

Higher frequency of hospitalization but lower relative mortality for pandemic influenza in people with type 2 diabetes

BACKGROUND

There is limited evidence linking type 2 diabetes (T2D) to influenza-related complications.

OBJECTIVES

To test a set of research questions relating to pandemic influenza vaccination, hospitalization and mortality in people with and without T2D.

METHODS

In this population-based cohort study, we linked individual-level data from several national registers for all Norwegian residents aged 30 years or more as of January 2009. People with or without T2D at baseline (n = 2 992 228) were followed until December 2013. We used Cox regression to estimate adjusted hazard ratios (aHRs).

RESULTS

Pandemic influenza hospitalization was more common in individuals with T2D (aHR = 2.46, 95% CI 2.04-2.98). The mortality hazard ratio associated with hospitalization for pandemic influenza was lower in people with T2D (aHR = 1.82, 95% CI 1.21-2.74) than in those without T2D (aHR = 3.89, 95% CI 3.27-4.62). The same pattern was observed when restricting to 90-day mortality (aHR = 3.89, 95% CI 1.25-12.06 amongst those with T2D and aHR = 10.79, 95% CI 7.23-16.10 amongst those without T2D). The rate of hospitalization for pandemic influenza was 78% lower in those vaccinated compared to nonvaccinated amongst people with T2D (aHR = 0.22, 95% CI 0.11-0.39), whilst the corresponding estimate for those without T2D was 59% lower (aHR = 0.41, 95% CI 0.33-0.52). Mortality was 25% lower in those vaccinated compared to nonvaccinated amongst people with T2D (aHR = 0.75, 95% CI 0.73-0.77), whilst the corresponding estimate for those without T2D was 9% (aHR = 0.91, 95% CI 0.90-0.92).

CONCLUSIONS

There may have been a lower threshold for pandemic influenza hospitalization for people with T2D, rather than more severe influenza infection. Our combined results support the importance of influenza vaccination amongst people with T2D, especially during pandemics.

Hospitalization following influenza infection and pandemic vaccination in multiple sclerosis patients: a nationwide population-based registry study from Norway

Patients with multiple sclerosis (MS) are at increased risk of infections and related worsening of neurological function. Influenza infection has been associated with increased risk of various neurological complications. We conducted a population-based registry study to investigate the risk of acute hospitalization of MS patients in relation to influenza infection or pandemic vaccination in Norway. The entire Norwegian population in the years 2008-2014 was defined as our study population (N = 5,219,296). Information on MS diagnosis, influenza infection and vaccination were provided by Norwegian national registries. The self-controlled case series method was used to estimate incidence rate ratios (IRRs) with 95% confidence intervals (95% CI) in defined risk periods. 6755 MS patients were identified during the study period. Average age at first registration of an MS diagnosis was 51.8 years among men and 49.9 years among females (66.9%). The IRR for emergency hospitalization among MS patients the first week after an influenza diagnosis was 3.4 (95% CI 2.4-4.8). The IRR was 5.6 (95% CI 2.7-11.3) after pandemic influenza, and 4.8 (95% CI 3.1-7.4) after seasonal influenza. Pandemic vaccination did not influence risk of hospitalization [IRR within the first week: 0.7 (95% CI 0.5-1.0)]. Among MS patients, influenza infection was associated with increased risk for acute hospitalization while no increased risk was observed after pandemic vaccination. Influenza vaccination could prevent worsening of MS-related symptoms as well as risk of hospitalization.

Association of Household Income With Life Expectancy and Cause-Specific Mortality in Norway, 2005-2015

IMPORTANCE

Examining causes of death and making comparisons across countries may increase understanding of the income-related differences in life expectancy.

OBJECTIVES

To describe income-related differences in life expectancy and causes of death in Norway and to compare those differences with US estimates.

DESIGN AND SETTING

A registry-based study including all Norwegian residents aged at least 40 years from 2005 to 2015.

EXPOSURES

Household income adjusted for household size.

MAIN OUTCOMES AND MEASURES

Life expectancy at 40 years of age and cause-specific mortality.

RESULTS

In total, 3 041 828 persons contributed 25 805 277 person-years and 441 768 deaths during the study period (mean [SD] age, 59.3 years [13.6]; mean [SD] number of household members per person, 2.5 [1.3]). Life expectancy was highest for women with income in the top 1% (86.4 years [95% CI, 85.7-87.1]) which was 8.4 years (95% CI, 7.2-9.6) longer than women with income in the lowest 1%. Men with the lowest 1% income had the lowest life expectancy (70.6 years [95% CI, 69.6-71.6]), which was 13.8 years (95% CI, 12.3-15.2) less than men with the top 1% income. From 2005 to 2015, the differences in life expectancy by income increased, largely attributable to deaths from cardiovascular disease, cancers, chronic obstructive pulmonary disease, and dementia in older age groups and substance use deaths and suicides in younger age groups. Over the same period, life expectancy for women in the highest income quartile increased 3.2 years (95% CI, 2.7-3.7), while life expectancy for women in the lowest income quartile decreased 0.4 years (95% CI, -1.0 to 0.2). For men, life expectancy increased 3.1 years (95% CI, 2.5-3.7) in the highest income quartile and 0.9 years (95% CI, 0.2-1.6) in the lowest income quartile. Differences in life expectancy by income levels in Norway were similar to differences observed in the United States, except that life expectancy was higher in Norway in the lower to middle part of the income distribution in both men and women.

CONCLUSIONS AND RELEVANCE

In Norway, there were substantial and increasing gaps in life expectancy by income level from 2005 to 2015. The largest differences in life expectancy between Norway and United States were for individuals in the lower to middle part of the income distribution.

Preeclampsia and Hypertension During Pregnancy in Areas with Relatively Low Levels of Traffic Air Pollution

Objectives Air pollution exposure may contribute to the development of preeclampsia and hypertension during pregnancy. However, the evidence for such a relation is still limited. We investigated the associations between exposure for moderate to low levels of air pollution during pregnancy and preeclampsia and gestational hypertension in selected urban and county areas of Norway. Methods This study used a sub-group of 17,533 women in the Norwegian Mother and Child Cohort Study. Air pollution levels at residential addresses were estimated using land use regression models and back-extrapolated to the period of each pregnancy. Information on preeclampsia and gestational hypertension were obtained from the Medical Birth Registry of Norway and information on lifestyle factors was collected from questionnaires completed by the women during pregnancy. Results Moderate mean levels of NO₂ (13.6 ± 6.9 µg/m³) at residential address during pregnancy were not associated with preeclampsia and pregnancy hypertension. We found no statistically significant associations per 10 µg/m³ change in NO₂ exposure and preeclampsia (adjusted OR 0.89, 95% CI 0.74, 1.08) or hypertension during pregnancy (adjusted OR 0.91, 95% CI 0.78, 1.06). Conclusions for Practice In this large Norwegian pregnancy cohort, we found no statistically significant associations for moderate to low levels of pregnancy NO₂ exposure and preeclampsia or hypertension during pregnancy.

Maternal history of miscarriages and measures of fertility in relation to childhood asthma

BACKGROUND

It remains unclear what underlies the greater risk of asthma reported among children conceived by assisted reproductive technologies (ART).

OBJECTIVE

Our aim was to clarify the role of parental subfertility and unmeasured confounding on the association between ART and childhood asthma, and to examine the possibility for common mechanisms underlying parental subfertility and miscarriages influencing asthma pathogenesis.

METHODS

We used data from national Norwegian health registries (n=474 402) and the Norwegian Mother and Child Cohort Study (MoBa) (n=75 797). We used log-linear regression to estimate overall associations, and fixed-effects logistic regression to estimate associations within siblings.

RESULTS

ART offspring had greater asthma risk, the adjusted relative risk (aRR) was 1.20 (95% CI 1.09 to 1.32) in the registry-based cohort, and 1.42 (95% CI 1.14 to 1.76) in MoBa. The sibling analysis yielded similar associations, although the CI included the null value. The elevated asthma risk among ART offspring was attenuated when they were compared with spontaneously conceived offspring with time to conception >12 months, aRR 1.22 (95% CI 0.95 to 1.57). Asthma risk also increased with maternal history of early miscarriages (≤12 weeks), with an aRR of 1.07 (95% CI 1.03 to 1.11) for one, aRR 1.18 (95% CI 1.10 to 1.26) for two and aRR 1.24 (95% CI 1.12 to 1.37) for three or more.

CONCLUSION

Our findings indicate that both parental subfertility and characteristics related to the ART procedure itself might increase offspring asthma risk, although this needs to be confirmed in future studies, and further suggest that common mechanisms underlying parental subfertility and recurrent miscarriages might influence offspring asthma pathogenesis.

Developing evidence-based recommendations for optimal interpregnancy intervals in high-income countries: protocol for an international cohort study

INTRODUCTION

Short interpregnancy interval (IPI) has been linked to adverse pregnancy outcomes. WHO recommends waiting at least 2 years after a live birth and 6 months after miscarriage or induced termination before conception of another pregnancy. The evidence underpinning these recommendations largely relies on data from low/middle-income countries. Furthermore, recent epidemiological investigations have suggested that these studies may overestimate the effects of IPI due to residual confounding. Future investigations of IPI effects in high-income countries drawing from large, population-based data sources are needed to inform IPI recommendations. We aim to assess the impact of IPIs on maternal and child health outcomes in high-income countries.

METHODS AND ANALYSIS

This international longitudinal retrospective cohort study will include more than 18 million pregnancies, making it the largest study to investigate IPI in high-income countries. Population-based data from Australia, Finland, Norway and USA will be used. Birth records in each country will be used to identify consecutive pregnancies. Exact dates of birth and clinical best estimates of gestational length will be used to estimate IPI. Administrative birth and health data sources with >99% coverage in each country will be used to identify maternal sociodemographics, pregnancy complications, details of labour and delivery, birth and child health information. We will use matched and unmatched regression models to investigate the impact of IPI on maternal and infant outcomes, and conduct meta-analysis to pool results across countries.

ETHICS AND DISSEMINATION

Ethics boards at participating sites approved this research (approval was not required in Finland). Findings will be published in peer-reviewed journals and presented at international conferences, and will inform recommendations for optimal IPI in high-income countries. Findings will provide important information for women and families planning future pregnancies and for clinicians providing prenatal care and giving guidance on family planning.

Vanishing twin syndrome among ART singletons and pregnancy outcomes

STUDY QUESTION

Among babies born by ART, do singleton survivors of a vanishing twin have lower birth weight than other singletons?

SUMMARY ANSWER

Vanishing twin syndrome (VTS) was associated with lower birth weight among ART singletons; a sibship analysis indicated that the association was not confounded by maternal characteristics that remain stable between deliveries.

WHAT IS KNOWN ALREADY

Previous studies indicate that ART singletons with VTS have increased risk of adverse pregnancy outcomes, compared with other ART singletons. The potential contribution of unmeasured maternal background characteristics has been unclear.

STUDY DESIGN, SIZE AND DURATION

This was a Norwegian population-based registry study, including 17 368 mothers with 20 410 ART singleton deliveries between January 1984 and December 2013.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The study population included 17 291 ART singletons without VTS, 638 ART singletons with VTS and 2418 ART singletons with uncertain vanishing twin status. We estimated differences in birth weight and gestational age comparing ART singletons with VTS first to all ART singletons without VTS, and subsequently to their ART siblings without VTS, using random- and fixed-effects linear regression, respectively. The corresponding comparisons for the associations with preterm birth and small for gestational age (SGA) were conducted using random-and fixed-effects logistic regression. The sibling analysis of preterm birth included 587 discordant siblings, while the sibling analysis of SGA included 674 discordant siblings.

MAIN RESULTS AND THE ROLE OF CHANCE

ART singletons with VTS had lower birth weight when compared to all ART singletons without VTS, with an adjusted mean difference (95% CI) of -116 g (-165, -67). When we compared ART singletons with VTS to their ART singletons sibling without VTS, the adjusted mean difference was -112 g (-209, -15). ART singletons with VTS also had increased risk of being born SGA, with an adjusted odds ratio (OR) (95% CI) of 1.48 (1.07, 2.03) compared to all ART singletons without VTS, and 2.79 (1.12, 6.91) in the sibship analyses. ART singletons with VTS were also more likely to be born preterm, although this difference did not reach statistical significance.

LIMITATIONS REASONS FOR CAUTION

We did not have information on maternal socio-economic status, but this factor is accounted for in the sibship analyses. We also had no information on whether fresh or frozen embryos were replaced.

WIDER IMPLICATIONS OF THE FINDINGS

The reduction in birth weight and increased risk of SGA in ART singletons with VTS may suggest the presence of harmful intrauterine factors with long-term health impact. While vanishing twins are not routinely observed in naturally conceived pregnancies, loss of a twin is potentially a risk factor for the surviving foetus in any pregnancy. This could be further explored in large samples of naturally conceived pregnancies with the necessary information.

STUDY FUNDING/COMPETING INTEREST(S)

The authors of this study are supported in part by the UK Medical Research Council, US National Institute of Environmental Health Sciences and the Norwegian Research Council. The authors have no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

General practice consultations and use of prescription drugs after changes to school absence policy

BACKGROUND

New rules for absence with stricter requirements for documentation were introduced in upper secondary schools in the autumn of 2016. We investigated the use of general practice services and dispensing of prescription drugs among 16 – 18-year-olds in the autumn of 2016 and compared this with equivalent figures for the period 2013 – 15.

MATERIAL AND METHOD

We retrieved information on consultations in general practice (GP) and dispensing of prescription drugs to 15 – 18-year-olds in the period 2013 – 16 from the Directorate of Health’s system for control and payment of health reimbursements (KUHR) and the Norwegian Prescription Database respectively. The number of consultations and dispensing of drugs were compared to previous years using Poisson regression (reference year 2015). The incidence rate ratio (IRR) was used as an outcome measure.

RESULTS

The number of GP consultations for 16 – 18-year-olds was 30 % higher in the autumn of 2016 than in the autumn of 2015 (IRR 1.30, 95 % confidence interval (CI) 1.29 – 1.31). In the same period, the dispensing of drugs to this age group increased by 8 % (IRR 1.08, 95 % CI 1.08 – 1.09). Among the diagnosis groups, respiratory tract infections had the largest increase (IRR 2.21, 95 % CI 2.17 – 2.25). The largest increase in drug dispensing was found for remedies for coughs and colds (IRR 1.73, 95 % CI 1.65 – 1.80).

INTERPRETATION

The increase in consultations in general practice and dispensing of drugs to 16 – 18-year-olds coincided in time with the introduction of new rules for absence from school. We hold it to be highly likely that the changes were caused by the stricter rules for documentation of absence from school.

Neuraminidase inhibitors during pregnancy and risk of adverse neonatal outcomes and congenital malformations: population based European register study

Objective To evaluate the possible effects of exposure to neuraminidase inhibitors during embryo-fetal life with respect to adverse neonatal outcomes and congenital malformations.Design Population based multinational observational cohort study and meta-analysis.Setting National registers covering information on maternal healthcare, births, and prescriptions in Denmark, Norway, and Sweden and the EFEMERIS database from the Haute-Garonne district in France.Participants All women together with their singleton infants born between 1 January 2008 and 31 December 2010. Only infants born at 154 days of gestation or later were included. Infants were defined as exposed if the women filled a prescription during pregnancy for either of the two neuraminidase inhibitors oseltamivir or zanamivir.Main outcomes Low birth weight, low Apgar score, preterm birth, small for gestational age birth, stillbirth, neonatal mortality, neonatal morbidity, and congenital malformations. Crude and adjusted hazard ratios of preterm birth were estimated using Cox regression models. Crude and adjusted odds ratios for other outcomes were estimated by logistic regression models.Results The study included 5824 (0.8%) exposed women and their infants and 692 232 who were not exposed. Exposure to neuraminidase inhibitors in utero was not associated with increased risks of any of the investigated neonatal outcomes, including low birth weight (adjusted odds ratio 0.77, 95% confidence interval 0.65 to 0.91), low Apgar score (adjusted odds ratio 0.87, 0.67 to 1.14), preterm birth (adjusted hazard ratio 0.97, 0.86 to 1.10), small for gestational age birth (adjusted odds ratio 0.72, 0.59 to 0.87), stillbirth (adjusted odds ratio 0.81, 0.51 to 1.30), neonatal mortality (adjusted odds ratio 1.13, 0.56 to 2.28), and neonatal morbidity (adjusted odds ratio 0.92, 0.86 to 1.00). No increased risk of congenital malformations overall associated with maternal exposure was observed during the first trimester (adjusted odds ratio 1.06, 0.77 to 1.48). Similarly, no significantly increased risks of any of the outcomes were observed in an analysis restricted to oseltamivir alone.Conclusions This large multinational register study found no increased risks of adverse neonatal outcomes or congenital malformations associated with exposure to neuraminidase inhibitors during embryo-fetal life. The results support previously reported findings that the use of neuraminidase inhibitors is not associated with increased risks of adverse fetal or neonatal outcomes.

Prediction of gestational age based on genome-wide differentially methylated regions

Background

We explored the association between gestational age and cord blood DNA methylation at birth and whether DNA methylation could be effective in predicting gestational age due to limitations with the presently used methods. We used data from the Norwegian Mother and Child Birth Cohort study (MoBa) with Illumina HumanMethylation450 data measured for 1753 newborns in two batches: MoBa 1, n = 1068; and MoBa 2, n = 685. Gestational age was computed using both ultrasound and the last menstrual period. We evaluated associations between DNA methylation and gestational age and developed a statistical model for predicting gestational age using MoBa 1 for training and MoBa 2 for predictions. The prediction model was additionally used to compare ultrasound and last menstrual period-based gestational age predictions. Furthermore, both CpGs and associated genes detected in the training models were compared to those detected in a published prediction model for chronological age.

Results

There were 5474 CpGs associated with ultrasound gestational age after adjustment for a set of covariates, including estimated cell type proportions, and Bonferroni-correction for multiple testing. Our model predicted ultrasound gestational age more accurately than it predicted last menstrual period gestational age.

Conclusions

DNA methylation at birth appears to be a good predictor of gestational age. Ultrasound gestational age is more strongly associated with methylation than last menstrual period gestational age. The CpGs linked with our gestational age prediction model, and their associated genes, differed substantially from the corresponding CpGs and genes associated with a chronological age prediction model.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-016-1063-4) contains supplementary material, which is available to authorized users.

Comorbidity and Childhood Epilepsy: A Nationwide Registry Study

BACKGROUND AND OBJECTIVE

Children with epilepsy are at increased risk of other disorders and difficulties, preceding, cooccurring with, or after the diagnosis of epilepsy. Risk estimates vary, few studies are population-based, and few provide comprehensive assessments of comorbidities. We used nationwide registry data to describe frequencies of medical, neurologic, developmental, and psychiatric conditions occurring before and after children are diagnosed with childhood epilepsy.

METHODS

Data were obtained from the Norwegian Patient Registry, which is an administrative database recording International Classification of Diseases, 10th Revision diagnoses from all government-funded specialist health services in Norway (outpatient consultations and hospitalizations). We included data from the years 2008 through 2013 for all children born in Norway between 1996 and 2013 (0-17 years of age at the end of follow-up). Children with epilepsy were compared with the general child population, adjusting for sex and age. We also compared children with complicated epilepsies (ie, epilepsies with additional neurologic and/or developmental disorders) to children with uncomplicated epilepsies.

RESULTS

The study population included 1 125 161 children. There were 6635 (0.6%) children with epilepsy. Nearly 80% of children with epilepsy had ≥1 comorbid disorder. All types of disorders were more frequent in children with epilepsy, with additional medical disorders recorded in 55%, neurologic disorders in 41%, and developmental/psychiatric disorders in 43%. Children with complicated epilepsies had the highest overall levels of comorbidity, but the risk of medical and psychiatric comorbidities was also substantial among children with uncomplicated epilepsies.

CONCLUSIONS

The overall frequency of comorbid disease is high in children with epilepsy, including children with presumably uncomplicated epilepsies.

Association between pregnancy exposure to air pollution and birth weight in selected areas of Norway

BACKGROUND

Exposure to air pollution has adverse effects on cardiopulmonary health of adults. Exposure to air pollution in pregnancy may affect foetal development. However, the evidence of such effect remains inconsistent. We investigated the effects of exposure to air pollution during pregnancy on birth outcomes.

METHODS

This study, based within the Norwegian Mother and Child Cohort Study (MoBa), includes 17,533 participants living in the two largest cities in Norway: Oslo and Bergen, and their two surrounding counties: Akershus and Hordaland. Air pollution levels at residential addresses were estimated using land use regression models and back-extrapolated to the period of each pregnancy using continuous monitoring station data. Birth outcomes were birth weight, low birth weight, gestational age, and preterm delivery obtained from the Medical Birth Registry of Norway. Information on lifestyle factors was collected from MoBa questionnaires completed by mothers during pregnancy. Linear and logistic regression models were used to analyse the associations between pregnancy NO2 exposure and birth outcomes.

RESULTS

We found a statistically significant negative association between pregnancy exposure to NO2 and birth weight -43.6 (95%CI -55.8 to -31.5) g per 10 μg/m(3) NO2. However, after adjusting for either area or the combination of parity and maternal weight, no substantive effects of air pollution exposure were evident.

CONCLUSIONS

Exposure to air pollution during pregnancy was associated with decrease in birth weight, but area-related and lifestyle factors attenuated this association. We found no statistically significant associations of air pollution exposure with gestational age, low birth weight or preterm delivery.

25-Hydroxyvitamin D in pregnancy and genome wide cord blood DNA methylation in two pregnancy cohorts (MoBa and ALSPAC)

The aim of the study was to investigate whether maternal mid-pregnancy 25-hydroxyvitamin D concentrations are associated with cord blood DNA methylation. DNA methylation was assessed using the Illumina HumanMethylation450 BeadChip, and maternal plasma 25-hydroxyvitamin D was measured in 819 mothers/newborn pairs participating in the Norwegian Mother and Child Cohort (MoBa) and 597 mothers/newborn pairs participating in the Avon Longitudinal Study of Parents and Children (ALSPAC). Across 473,731CpG DNA methylation sites in cord blood DNA, none were strongly associated with maternal 25-hydroxyvitamin D after adjusting for multiple tests (false discovery rate (FDR)>0.5; 473,731 tests). A meta-analysis of the results from both cohorts, using the Fisher method for combining p-values, also did not strengthen findings (FDR>0.2). Further exploration of a set of CpG sites in the proximity of four a priori defined candidate genes (CYP24A1, CYP27B1, CYP27A1 and CYP2R1) did not result in any associations with FDR<0.05 (56 tests). In this large genome wide assessment of the potential influence of maternal vitamin D status on DNA methylation, we did not find any convincing associations in 1416 newborns. If true associations do exist, their identification might require much larger consortium studies, expanded genomic coverage, investigation of alternative cell types or measurements of 25-hydroxyvitamin D at different gestational time points.

Febrile seizures after 2009 influenza A (H1N1) vaccination and infection: a nationwide registry-based study

Background

During the 2009 influenza A (H1N1) pandemic, a monovalent pandemic strain vaccine containing the oil-in-water adjuvant AS03 (Pandemrix®) was offered to the Norwegian population. The coverage among children reached 54 %. Our aim was to estimate the risk of febrile seizure in children after exposure to pandemic influenza vaccination or infection.

Methods

The study population comprised 226,889 children born 2006–2009 resident in Norway per October 1st, 2009. Febrile seizure episodes were defined by emergency hospital admissions / emergency outpatient hospital care with International Classification of Diseases, Version 10, codes R56.0 or R56.8. The self-controlled case series method was applied to estimate incidence rate ratios (IRRs) in pre-defined risk periods compared to the background period. The total observation window was ± 180 days from exposure day. Among 113,068 vaccinated children, 656 (0.6 %) had at least one febrile seizure episode.

Results

The IRR of febrile seizures 1–3 days after vaccination was 2.00 (95 % confidence interval [CI]: 1.15–3.51). In the period 4–7 days after vaccination, no increased risk was observed. Among the 8172 children diagnosed with pandemic influenza, 84 (1.0 %) had at least one febrile seizure episode. The IRR of febrile seizures on the same day as a diagnosis of influenza was 116.70 (95 % CI: 62.81–216.90). In the period 1–3 days after a diagnosis of influenza, a tenfold increased risk was observed (IRR 10.12, 95 % CI: 3.82 – 26.82).

Conclusions

In this large population-based study with precise timing of exposures and outcomes, we found a twofold increased risk of febrile seizures 1–3 days after pandemic influenza vaccination. However, we found that pandemic influenza infection was associated with a much stronger increase in risk of febrile seizures.

Risk of Guillain-Barré syndrome after exposure to pandemic influenza A(H1N1)pdm09 vaccination or infection: a Norwegian population-based cohort study

Vaccinations and infections are possible triggers of Guillain-Barré syndrome (GBS). However, studies on GBS after vaccinations during the influenza A(H1N1)pmd09 pandemic in 2009, show inconsistent results. Only few studies have addressed the role of influenza infection. We used information from national health data-bases with information on the total Norwegian population (N = 4,832,211). Cox regression analyses with time-varying covariates and self-controlled case series was applied. The risk of being hospitalized with GBS during the pandemic period, within 42 days after an influenza diagnosis or pandemic vaccination was estimated. There were 490 GBS cases during 2009-2012 of which 410 cases occurred after October 1, 2009 of which 46 new cases occurred during the peak period of the influenza pandemic. An influenza diagnosis was registered for 2.47% of the population and the vaccination coverage was 39.25%. The incidence rate ratio of GBS during the pandemic peak relative to other periods was 1.46 [95% confidence interval (CI) 1.08-1.98]. The adjusted hazard ratio (HR) of GBS within 42 days after a diagnosis of pandemic influenza was 4.89 (95% CI 1.17-20.36). After pandemic vaccination the adjusted HR was 1.11 (95% CI 0.51-2.43). Our results indicated that there was a significantly increased risk of GBS during the pandemic season and after pandemic influenza infection. However, vaccination did not increase the risk of GBS. The small number of GBS cases in this study warrants caution in the interpretation of the findings.

Causal pathways for asthma (CASPAR) – MoBa “a happy hunting ground”

Large population-based research cohorts, together with national health registries and biobanks are core components in a modern infrastructure for knowledge. Along with the other Nordic countries, Norway has unique opportunities for high quality research based on cohorts, biobanks and registries. Cohorts, biobanks and registries provide a basis for discovering causes and mechanisms of disease as well as for following the development of disease, effects of treatment and consequences of disease. The purpose of this manuscript is to give a brief outline of a project that makes use of these unique opportunities by using data from The Norwegian Mother and Child cohort study (MoBa) to address research questions of common interest, and thus encourage other research groups to use this “happy hunting ground”.The present study, Causal Pathways for Asthma (CASPAR) funded by the Research Council of Norway, is a subproject of MoBa. The project is designed to take advantage of the potential for research on human biological material in biobanks, by coupling analysis results with data from health surveys, health registries and the health services. The present study is based on an ongoing collaboration between the Norwegian Institute of Public Health (NIPH), the National Institute of Environmental Health Sciences (NIEHS) in the US and several other national and international collaborators within The MoBa Asthma Group. The main aim of the study is to examine a number of hypothesis regarding in utero and early life exposures in relation to the development of different phenotypes of asthma and allergies in childhood.For the majority of children who become asthmatic and allergic, the differentiation of their immune system into an atopic phenotype probably begins before birth and is established within the first six years of life. This study will advance knowledge of the mechanisms whereby diet and environmental exposures influences gene expression to alter risk of atopic disease. The prime purpose is to build up new knowledge on asthma pathogenesis. There is a great need to develop a new paradigm of disease pathogenesis that takes advantages of applied molecular approaches to asthma and atopic diseases as it occurs in humans at different stages of development. This project takes advantage not only of the basic MoBa samples and infrastructure including links to other national health registries, but also a new national supplementary study of MoBa that includes measures of prenatal exposures in maternal plasma believed to have epigenetic influences on asthma/atopy development and data on genome wide methylation of cord blood DNA.

Two age peaks in the incidence of chronic fatigue syndrome/myalgic encephalomyelitis: a population-based registry study from Norway 2008-2012

BACKGROUND

The aim of the current study was to estimate sex- and age-specific incidence rates of chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME) using population-based registry data. CFS/ME is a debilitating condition with large impact on patients and their families. The etiology is unknown, and the distribution of the disease in the general population has not been well described.

METHODS

Cases of CFS/ME were identified in the Norwegian Patient Register (NPR) for the years 2008 to 2012. The NPR is nationwide and contains diagnoses assigned by specialist health care services (hospitals and outpatient clinics). We estimated sex- and age-specific incidence rates by dividing the number of new cases of CFS/ME in each category by the number of person years at risk. Incidence rate ratios were estimated by Poisson regression with sex, age categories, and year of diagnosis as covariates.

RESULTS

A total of 5,809 patients were registered with CFS/ME during 2008 to 2012. The overall incidence rate was 25.8 per 100,000 person years (95% confidence interval (CI): 25.2 to 26.5). The female to male incidence rate ratio of CFS/ME was 3.2 (95% CI: 3.0 to 3.4). The incidence rate varied strongly with age for both sexes, with a first peak in the age group 10 to 19 years and a second peak in the age group 30 to 39 years.

CONCLUSIONS

Early etiological clues can sometimes be gained from examination of disease patterns. The strong female preponderance and the two age peaks suggest that sex- and age-specific factors may modulate the risk of CFS/ME.

Prenatal and postnatal parental smoking and acute otitis media in early childhood

AIM

To explore the associations between acute otitis media in early childhood and prenatal and postnatal tobacco smoke exposure.

METHODS

Subjects were 32 077 children born between 2000 and 2005 in the Norwegian Mother and Child Study with questionnaire data on tobacco smoke exposure and acute otitis media up to 18 months of age. Multivariate regression models were used to obtain adjusted relative risks for acute otitis media.

RESULTS

Acute otitis media was slightly more common in children exposed to parental smoking. The incidence from 0 to 6 months was 4.7% in unexposed children and 6.0% in children exposed both prenatally and postnatally. After adjusting for postnatal exposure and covariates, the relative risk for acute otitis media 0-6 months when exposed to maternal smoking in pregnancy was 1.34, 95% confidence interval: 1.06-1.69. Maternal smoking in pregnancy was associated with acute otitis media up to 12 months of age. Compared with non-exposed children, there was a slightly increased risk of recurrent acute otitis media for children exposed both prenatally and postnatally with a relative risk of 1.24, 95% confidence interval: 1.01-1.52.

CONCLUSION

Even in a cohort with relatively low exposure levels of parental smoking, maternal smoking in pregnancy was associated with an increased risk of acute otitis media in early childhood.