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Jonas F Ludvigsson,1,2 Siri E Håberg,3 Gun Peggy Knudsen,3 Pierre Lafolie,4,5 Helga Zoega,6 Catharina Sarkkola,7 Stephanie von Kraemer,7 Elisabete Weiderpass,1,7–10 Mette Nørgaard11 1Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, 2Department of Pediatrics, Örebro University Hospital, Örebro, Sweden; 3Norwegian Institute of Public Health, Oslo, Norway; 4Department of Medicine, Clinical Pharmacology Unit, 5The Stockholm Regional Ethical Review Board, Karolinska Institutet, Stockholm, Sweden; 6Center of Public Health Sciences, Faculty of Medicine, University of Iceland, Reykjavík, Iceland; 7Genetic Epidemiology Group, Folkhälsan Research Center, Helsinki, Finland; 8Department of Community Medicine, Faculty of Health Sciences, University of Tromsø, 9The Arctic University of Norway, Tromsø, 10Department of Research, Cancer Registry of Norway, Oslo, Norway; 11Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark Abstract: National health care registries in the Nordic countries share many attributes, but different legal and ethical frameworks represent a challenge to promoting effective joint research. Internationally, there is a lack of knowledge about how ethical matters are considered in Nordic registry-based research, and a lack of knowledge about how Nordic ethics committees operate and what is needed to obtain an approval. In this paper, we review ethical aspects of registry-based research, the legal framework, the role of ethics review boards in the Nordic countries, and the structure of the ethics application. We discuss the role of informed consent in registry-based research and how to safeguard the integrity of study participants, including vulnerable subjects and children. Our review also provides information on the different government agencies that contribute registry-based data, and a list of the major health registries in Denmark, Finland, Iceland, Norway, and Sweden. Both ethical values and conditions for registry-based research are similar in the Nordic countries. While Denmark, Finland, Iceland, Norway, and Sweden have chosen different legal frameworks, these differences can be resolved through mutual recognition of ethical applications and by harmonizing the different systems, likely leading to increased collaboration and enlarged studies. Keywords: ethical review, ethics, institutional review board, Nordic countries, registry-based research, informed consent

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. Pregnant women are at increased risk of hospitalisation for COVID‐19. Pregnant women are at increased risk of hospitalisation for COVID‐19. [ABSTRACT FROM AUTHOR]

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. Short versus long interpregnancy intervals associated with higher ORs for preterm birth (PTB) after a previous PTB. Short versus long interpregnancy intervals associated with higher ORs for preterm birth (PTB) after a previous PTB. [ABSTRACT FROM AUTHOR]

Compelling evidence suggests a causal relation between parental smoking during and after pregnancy and adverse effects on respiratory health in the offspring. The authors' aim in this study was to disentangle the effects of prenatal and postnatal smoking on early childhood respiratory health. Most parents who smoke during pregnancy continue to smoke postpartum, and it is difficult to identify sufficiently large subgroups of children who were exclusively exposed in utero or after birth. This study was based on the first 22,390 children born between 2000 and 2004 in the Norwegian Mother and Child Cohort, a pregnancy cohort designed to eventually include 100,000 pregnancies. Data were collected through detailed questionnaires administered at various stages of pregnancy, starting in early pregnancy. Because of the large study population, the authors were able to disentangle the pre- and postnatal effects of parental smoking on wheeze and lower respiratory tract infection in the children's first 18 months of life. They found maternal smoking in pregnancy to be an independent risk factor for wheeze and respiratory infection. Postnatal paternal smoking was also associated with these outcomes, independently of maternal smoking in pregnancy. [ABSTRACT FROM AUTHOR]

This study evaluated the relationship between Covid-19 vaccination and menstrual bleeding disturbances using a large national registry linkage including 666,467 women between 20 and 40 years of age residing in Norway on January 1st, 2019. Information on vaccination-BNT162b2 and mRNA-1273 - was obtained from the Norwegian vaccination registry. Diagnoses of menstrual disturbances (absent/scanty, excessive, irregular/frequent menstruation, and intermenstrual bleeding) was obtained from the general practitioner database. We examined new-onset menstrual bleeding disturbances using a Cox regression comparing vaccinated to unvaccinated women, where women contributed follow-up time as unvaccinated until the day of vaccination. In addition, we conducted a self-controlled case-series analysis, and a sensitivity analysis excluding all those who remained unvaccinated throughout the pandemic, to evaluate the role of unmeasured confounding. We observed an increased risk of several menstrual bleeding disturbances after vaccination against Covid-19, ranging from an adjusted HR (aHR) of 1.18 (95% CI: 1.04, 1.33) for intermenstrual bleeding to 1.29 (95% CI: 1.23, 1.36) for irregular/frequent menstrual periods. However, estimates were fully attenuated when excluding women who remained unvaccinated at the end of follow-up (aHRs between 0.97 and 1.08). No differences were identified according to vaccine dose or type. Our self-controlled case series analysis confirmed no increased risk after a first dose of vaccination, though there was a slightly increased risk of menstrual bleeding disturbances from 61 days after vaccination with dose 2. In conclusion, the modestly increased risk of menstrual bleeding disturbances after Covid-19 vaccination appeared to reflect a role of unmeasured confounding by women who never received Covid-19 vaccinations, as associations did not remain when risk after vaccination were compared to risk before vaccination among ever vaccinated women., (© 2024. The Author(s).)

Objectives: To explore the association between antidepressant use during pregnancy and birth outcomes., Design: Cohort study., Setting: Electronic health record data., Participants: 2 528 916 singleton births from the UK's Clinical Practice Research Datalink (1996-2018), Norway's Medical Birth Registry (2009-2020), and Sweden's Medical Birth Register (2006-2020)., Main Outcome Measures: Stillbirth, neonatal death, pre- and post-term delivery, small and large for gestational age, and low Apgar score five minutes post-delivery., Results: A total of 120 209 (4.8%) deliveries were exposed to maternal antidepressant use during pregnancy. Maternal antidepressant use during pregnancy was associated with increased odds of stillbirth (adjusted pooled OR (aOR) 1.16, 95% CI 1.05 to 1.28), preterm delivery (aOR 1.26, 95% CI 1.23 to 1.30), and Apgar score < 7 at 5 minutes (aOR 1.83, 95% CI 1.75 to 1.91). These findings persisted in the discordant sibling analysis, but with higher uncertainty. The adjusted predicted absolute risk for stillbirth was 0.34% (95% CI 0.33 to 0.35) among the unexposed and 0.40% (95% CI 0.36 to 0.44) in the antidepressant exposed. Restricting to women with depression or anxiety, the association between antidepressant exposure and stillbirth attenuated (aOR 1.07, 95% CI 0.94 to 1.21). Paternal antidepressant use was modestly associated with preterm delivery and low Apgar score. Most antidepressants were associated with preterm delivery (except paroxetine) and Apgar score (except mirtazapine and amitriptyline)., Conclusions: Maternal antidepressant use during pregnancy may increase the risk of stillbirth, preterm delivery, and low Apgar score, although the absolute risks remained low. Confounding by severity of indication cannot be ruled out, as the severity of symptoms was not available. The modest association between paternal antidepressant use and both preterm delivery and low Apgar score suggests that residual confounding by familial environment cannot be ruled out.

Background: Cancer is the leading cause of disease-related mortality in children. Causes of leukemia, the most common form, are largely unknown. Growing evidence points to an origin in-utero, when global redistribution of DNA methylation occurs driving tissue differentiation., Methods: Epigenome-wide DNA methylation was profiled in surrogate (blood) and target (bone marrow) tissues at birth, diagnosis, remission and relapse of pediatric pre-B acute lymphoblastic leukemia (pre-B ALL) patients. Double-blinded analyses was performed between prospective cohorts extending from birth to diagnosis and retrospective studies backtracking from clinical disease to birth. Validation was carried out using independent technologies and populations., Results: The imprinted and immuno-modulating VTRNA2-1 was hypermethylated (FDR<0.05) at birth in nested cases relative to controls in all tested populations (totaling 317 cases and 483 controls), including European and Hispanic ancestries. VTRNA2-1 methylation was stable over follow-up years after birth and across surrogate, target and other tissues (n=5,023 tissues; 30 types). When profiled in leukemic tissues from two clinical cohorts (totaling 644 cases), VTRNA2-1 methylation exhibited higher levels at diagnosis relative to controls, it reset back to normal levels at remission, and then re-increased to above control levels at relapse. Hypermethylation was significantly associated with worse pre-B ALL patient survival and with reduced VTRNA2-1 expression (n=2,294 tissues; 26 types), supporting a functional and translational role for VTRNA2-1 methylation., Conclusion: This study provides proof-of-concept to detect at birth epigenetic precursors of pediatric pre-B ALL. These alterations were reproducible with different technologies, in three continents and in two ethnicities, and can offer biomarkers for early detection and prognosis as well as actionable targets for therapy., (© 2024. The Author(s).)

Study Question: Is there an association between male or female epigenetic age acceleration (EAA) or deceleration (EAD) and fecundability?, Summary Answer: We do not find compelling evidence of an association between EAA or EAD and fecundability., What Is Known Already: Prior research has shown that female accelerated epigenetic aging is associated with unfavorable clinical fecundity outcomes and use of in vitro fertilization, and that epigenetic aging in sperm cells is associated with unfavorable sperm parameters. Studies of epigenetic aging and fecundability among individuals who conceive naturally are lacking., Study Design, Size, Duration: This study is based on the Norwegian Mother, Father and Child Cohort Study (MoBa), a population-based pregnancy cohort which recruited pregnant couples between 1999 and 2008. We used data from 1657 couples (women and men) with planned naturally conceived pregnancies and available blood samples., Participants/materials, Setting, Methods: Methylation levels were measured in DNA from blood samples taken recruitment (at ∼18 gestational weeks) from pregnant women and their partners using the Illumina Methylation EPIC Array. To obtain a measure of EAA/EAD, we performed a linear regression of each of seven different established epigenetic biomarkers (DNAmAge by Horvath, DNAmAge by Hannum et al., PhenoAge by Levine et al., DunedinPoAm by Belsky et al., DunedinPACE by Belsky et al., DNAmTL by Lu et al., and GrimAge by Lu et al.) against chronological age. We fitted proportional probability regression models to obtain fecundability ratios (FRs) for each standard deviation increase in epigenetic aging, and obtained crude and adjusted (for body mass index, smoking, and education level) estimates. Results were evaluated at a false discovery rate (FDR) of 5%. We evaluated all models for non-linear associations using categories of epigenetic age where appropriate., Main Results and the Role of Chance: Although the DunedinPACE clock in males demonstrated slightly increasing fecundability with increasing EAA (adjusted FR 1.05 per one standard deviation increase in EAA, 95% CI 1.00-1.10), this was not robust when evaluated at an FDR of 5%. We found evidence of non-linearity between biological aging and fecundability in two models in females and three models in males, but non-linear associations were weak and conflicting., Limitations, Reasons for Caution: As MoBa is a pregnancy cohort, our findings may not be generalizable to all couples attempting conception. Fecundability is a couple-level measure, and any impacts of epigenetic aging in each partner may be obscured by effects of the other partner., Wider Implications of the Findings: Our findings contrast with those of prior studies, which have indicated an association between EAA and unfavorable clinical fertility outcomes in populations using fertility treatments, possibly due to less important effects of epigenetic aging among couples who conceive naturally. More research is needed on the association between blood-based EAA and clinical fertility parameters in both sexes., Study Funding/competing Interest(s): The study was supported by the Research Council of Norway through its Medical Student Research Program funding scheme (project number 271555/F20), its Centres of Excellence funding scheme (project number 262700), and a grant from the Women's Health Program (320656). Co-funding was also received from the Strategic Research Council (SRC), FLUX consortium, decision numbers 345130 and 345131; the National Institute on Aging (R01AG075208); grants to the Max Planck-University of Helsinki Center from the Max Planck Society (decision number 5714240218), Jane and Aatos Erkko Foundation, Faculty of Social Sciences at the University of Helsinki, and Cities of Helsinki, Vantaa, and Espoo; and the European Research Council; and the European Research Council (ERC Synergy, BIOSFER, grant number 101071773, and the Horizon 2020 research and innovation program, grant number 947684). The authors declare no conflicts of interest., Trial Registration Number: N/A., (© The Author(s) 2024. Published by Oxford University Press on behalf of European Society of Human Reproduction and Embryology.)

Background: Snuff is a smokeless source of nicotine that is common in Scandinavia and increasingly used by women of fertile age. Persistent use of snuff during pregnancy has been associated with adverse pregnancy outcomes. Emerging data from the Medical Birth Registry of Norway distinguishes between occasional use and daily use. We provide preliminary estimates of associations between frequency of snuff and gestational length and birth weight., Methods: Data on snuff use during pregnancies delivered in 2020 and 2021 were available for the west and central regions of Norway. Associations of snuff use with gestational length and birth weight at term (39-41 weeks) were estimated using quantile regression at the 25th, the 50th and the 75th percentiles, with adjustments for mother's age, pre-pregnancy weight, and parity. We compared associations with the pregnancy outcomes according to maternal snuff and cigarette use., Results: 12.4% of 18 042 non-smoking women reported daily use of snuff before pregnancy, and 4.6% reported continuing use during pregnancy, with 1.2% still reporting daily use in the last trimester. Women with daily use through the last trimester delivered babies with a median gestational length reduced by 3.4 days (95% CI: -5.0 to -1.7 days) compared with women who never used snuff. The reduction was even stronger at the 25th percentile of gestational age. The median term birth weight was reduced by 44 g (95% CI: -134 to 46 g). These associations were much weaker for women who quit snuff at some point during pregnancy or used snuff only occasionally. Mothers who smoked daily through the last trimester had a median gestational length reduced by 2.1 days (95% CI: -2.7 to -1.4) and a median term birth weight reduced by 294 g (95% CI: -325 to -262) compared with never-smokers., Conclusions: Daily snuff use through the last trimester reduced the median gestational length by more than three days. Snuff reduced birth weight, but not as much as smoking, suggesting that the predominant effect of smoking on fetal growth is not through nicotine but through the additional toxic chemicals in cigarettes or by reduced oxygen supply to the fetus., (© 2024. The Author(s).)

Previous studies have shown cord-blood DNA methylation differences in newborns conceived using assisted reproductive technologies (ART) compared to those conceived naturally. However, whether these ART-related DNA methylation differences vary with children's sex is unknown. We hypothesize that the DNA methylation differences in cord blood between ART-conceived and naturally conceived newborns also varies by the sex of the child, with distinct patterns of differential methylation present in males and females. We investigated sex differences in cord-blood DNA methylation variation according to conception by ART using the Illumina MethylationEPIC platform, comparing 456 ART-conceived versus 507 naturally-conceived girls, and 503 ART-conceived and 473 naturally-conceived boys. We identified 37 differentially methylated CpGs according to ART-conception among girls, and 70 differentially methylated CpGs according to ART-conception among boys, when we used a 1% false discovery rate to account for multiple testing. Ten CpGs were differentially methylated according to conception by ART in both sexes. Among the genes that were associated with these CpGs, we found the BRCA1; NBR2 gene (two CpGs) was hypermethylated in girls while the APC2 (two CpGs) and NECAB3;ACTL10, (four CpGs) related to cellular signaling were hypomethylated in boys. These findings confirm the presence of sex-specific epigenetic differences, illustrating the nuanced impact of ART on the fetal epigenome. There is a need for further explorations into the implications for sex-specific developmental trajectories and health outcomes in ART-conceived children., (© 2024. The Author(s).)

Purpose: To investigate the association between sibling relatedness and pubertal development in girls and boys., Methods: This cohort study consisted of 10,657 children from the Puberty Cohort, Denmark. Information on sibling relatedness was obtained by self-report. Information on pubertal markers was obtained half yearly from age 11 and throughout puberty. Mean age difference at attaining pubertal markers was estimated using interval-censored regression models according to sibling relatedness (full, half and/or step siblings; half and/or step siblings; no siblings; relative to full siblings)., Results: Girls with both full, half and/or step siblings (-1.2 (CI 95 %: -2.5; 0.1) months), only half- and/or stepsiblings (-2.2 (CI 95 %: -3.7; -0.7) months), and no siblings (-5.5 (CI 95 %: -8.5; -2.5) months) entered puberty earlier than girls with full siblings. Boys with full, half and/or step siblings (-1.4 (CI 95 %: -2.7; -0.1) months), only half and/or step siblings (-1.2 (CI 95 %: -3.0; 0.6) months), and no siblings (-4.5 (CI 95 %: -8.8; -0.3) months) entered puberty earlier than boys with full siblings., Conclusions: Children with sibling relatedness other than full siblings entered puberty earlier than their peers with full siblings even after adjustment for parental cohabitation status, childhood body mass index and childhood internalizing and externalizing symptoms., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Cecilia H. Ramlau-Hansen, Siri Eldevik Haberg, Mikko Myrskyla reports financial support was provided by European Research Council. Cecilia Ramlau-Hansen reports financial support was provided by Independent Research Fund Denmark. Cecilia H. Ramlau-Hansen reports financial support was provided by Independent Research Fund Denmark Health and Disease. Mikko Myrskyla reports financial support was provided by Strategic Research Council. Mikko Myrskyla reports financial support was provided by National Institute on Aging. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Disclosure of interest All authors declare no conflicts of interest. CHR declares to have received funding from the Danish Council for Independent Research (DFF 4183–00152), the Independent Research Fund Denmark (FSS 0602–02738B), the European Union (ERC, BIOSFER, 101071773). SEH declares to have received funding from the Research Council of Norway through its Centres of Excellence funding scheme (project No 262700), the European Union (ERC, BIOSFER, 101071773). MM declares to have received funding from the European Union (ERC, BIOSFER, 101071773), the Strategic Research Council (SRC), FLUX consortium, decision numbers 345130 and 345131; by the National Institute on Aging (R01AG075208); from any grants to the Max Planck – University of Helsinki Center from the Max Planck Society, Jane and Aatos Erkko Foundation, Faculty of Social Sciences at the University of Helsinki, and Cities of Helsinki, Vantaa and Espoo. The funding sources were not involved in the preparation, analysis, and interpretation of the data or submission of this report., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Aims: The overarching aim of this study was to evaluate the Norwegian guidelines for growth monitoring using routinely collected data from healthy children up to five years of age. We analysed criteria for both status (size for age) and change (centile crossing) in growth., Methods: Longitudinal data were obtained from the electronic health record (EHR) at the well-baby clinic for 2130 children included in the Bergen growth study 1 (BGS1). Measurements of length, weight, weight-for-length, body mass index (BMI) and head circumference were converted to z -scores and compared with the World Health Organization (WHO) growth standards and the national growth reference., Results: Using the WHO growth standard, the proportion of children above +2SD was generally higher than the expected 2.3% for all traits at birth and for length at all ages. Crossing percentile channels was common during the first two years of life, particularly for length/height. By the age of five years, 37.9% of the children had been identified for follow-up regarding length/height, 33% for head circumference and 13.6% for high weight-for-length/BMI., Conclusions: The proportion of children beyond the normal limits of the charts is higher than expected, and a surprisingly large number of children were identified for rules concerning length or growth in head circumference. This suggests the need for a revision of the current guidelines for growth monitoring in Norway., Competing Interests: Declaration of conflicting interestsThe authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Objectives: To evaluate the risk of major congenital anomalies according to infection with or vaccination against covid-19 during the first trimester of pregnancy., Design: Prospective Nordic registry based study., Setting: Sweden, Denmark, and Norway., Participants: 343 066 liveborn singleton infants in Sweden, Denmark, and Norway, with an estimated start of pregnancy between 1 March 2020 and 14 February 2022, identified using national health registries., Main Outcome Measure: Major congenital anomalies were categorised using EUROCAT (European Surveillance of Congenital Anomalies) definitions. The risk after covid-19 infection or vaccination during the first trimester was assessed by logistic regression, adjusting for maternal age, parity, education, income, country of origin, smoking, body mass index, chronic conditions, and estimated date of start of pregnancy., Results: 17 704 (5.2%) infants had a major congenital anomaly. When evaluating risk associated with covid-19 infection during the first trimester, the adjusted odds ratio ranged from 0.84 (95% confidence interval 0.51 to 1.40) for eye anomalies to 1.12 (0.68 to 1.84) for oro-facial clefts. Similarly, the risk associated with covid-19 vaccination during the first trimester ranged from 0.84 (0.31 to 2.31) for nervous system anomalies to 1.69 (0.76 to 3.78) for abdominal wall defects. Estimates for 10 of 11 subgroups of anomalies were less than 1.04, indicating no notable increased risk., Conclusions: Covid-19 infection and vaccination during the first trimester of pregnancy were not associated with risk of congenital anomalies., Competing Interests: Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/disclosure-of-interest/ and declare: support from Research Council of Norway, NordForsk, European Research Council for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work., (© Author(s) (or their employer(s)) 2019. Re-use permitted under CC BY. No commercial re-use. See rights and permissions. Published by BMJ.)

BackgroundSocioeconomic status in the risk of developing type 1 diabetes seems inconsistent. We investigated whether risk of childhood-onset type 1 diabetes differed by parental education or occupation in a nationwide cohort., Methods: This cohort study included all children born in Norway from 1974 to 2013. In individually linked data from nationwide population registries following children born in Norway up to 15 years of age, we identified 4647 with newly diagnosed type 1 diabetes during 15 381 923 person-years of follow-up., Results: Children of mothers with a master's degree had lower risk of type 1 diabetes than children of mothers with completed upper secondary education only (adjusted incidence rate ratio, aIRR=0.82 95% CI: 0.70 to 0.95). There was no difference between upper secondary and lower secondary maternal education (aIRR=0.98, 95% CI: 0.89 to 1.08). Paternal education was not significantly associated with type 1 diabetes, lower secondary compared with upper secondary aIRR 0.96 (0.88-1.05) and master compared with upper secondary aIRR 0.93 (0.83-1.05). While maternal elementary occupation was associated with a lower risk of type 1 diabetes, specific maternal or paternal occupations were not., Conclusions: Our results suggested inverse U-shaped associations between maternal socioeconomic status and risk of type 1 diabetes. Non-linear associations may be part of the reason why previous literature has been inconsistent., Competing Interests: Competing interests: PL-DR reports participation in a research project funded by LEO Pharma, all regulator mandated phase IV studies, all with funds paid to her institution (no personal fees) and with no relation to the work reported in this paper. All other authors declare no competing interests., (© Author(s) (or their employer(s)) 2024. No commercial re-use. See rights and permissions. Published by BMJ.)

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., (© The Author(s) 2024. Published by Oxford University Press on behalf of European Society of Human Reproduction and Embryology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

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/m 2 ) 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., (© 2023 The Authors. Paediatric and Perinatal Epidemiology published by John Wiley & Sons Ltd.)

Background: Studies indicate that individuals who deliver after assisted reproductive technologies (ART) may have an increased risk of cardiovascular disease (CVD). A recent large study from the U.S. showed a higher risk of stroke during the first year after delivery., Objectives: To compare the risk of stroke during the first year after delivery according to the use of ART in the Nordic countries., Methods: Registry-based cohort study using nationwide data from Denmark (1994-2014), Finland (1990-2014), Norway (1984-2015) and Sweden (1985-2015). Data on ART conception were available from ART quality registries and/or Medical Birth Registries (MBRs). National data on stroke were available from hospital and cause-of-death registries. The risk of stroke during the first year after delivery was estimated with Cox proportional hazard regression, adjusting for age, calendar year of delivery, multiple births, and country., Results: A total of 2,659,272 primiparous individuals had a registered delivery in the MBRs during the study period, and 91,466 (4%) of these gave birth after ART. We observed no overall increased risk of stroke during the first year after delivery among individuals conceiving after ART (adjusted hazard ratio [HR] 1.10, 95% CI 0.77, 1.57). Similarly, there was no convincing evidence that the short-term risk of stroke was higher within 1, 2, 3, or 6 months after delivery, with adjusted HRs ranging between 1.23 and 1.33 and confidence intervals including the null value for all time periods. A secondary analysis also including multiparous individuals (n = 3,335,478) at the start of follow-up yielded similar findings., Conclusions: We found no evidence of an increased short-term risk of stroke among individuals who delivered after using ART., (© 2023 The Authors. Paediatric and Perinatal Epidemiology published by John Wiley & Sons Ltd.)

Study Question: Are impaired glucose tolerance (as measured by fasting glucose, glycated hemoglobin, and fasting insulin) and cardiovascular disease risk (as measured by low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, triglycerides, systolic blood pressure, and diastolic blood pressure) causally related to infertility?, Summary Answer: Genetic instruments suggest that higher fasting insulin may increase infertility in women., What Is Known Already: Observational evidence suggests a shared etiology between impaired glucose tolerance, cardiovascular risk, and fertility problems., Study Design, Size, Duration: This study included two-sample Mendelian randomization (MR) analyses, in which we used genome-wide association summary data that were publicly available for the biomarkers of impaired glucose tolerance and cardiovascular disease, and sex-specific genome-wide association studies (GWASs) of infertility conducted in the Norwegian Mother, Father, and Child Cohort Study., Participants/materials, Setting, Methods: There were 68 882 women (average age 30, involved in 81 682 pregnancies) and 47 474 of their male partners (average age 33, 55 744 pregnancies) who had available genotype data and who provided self-reported information on time-to-pregnancy and use of ARTs. Of couples, 12% were infertile (having tried to conceive for ≥12 months or used ARTs to conceive). We applied the inverse variance weighted method with random effects to pool data across variants and a series of sensitivity analyses to explore genetic instrument validity. (We checked the robustness of genetic instruments and the lack of unbalanced horizontal pleiotropy, and we used methods that are robust to population stratification.) Findings were corrected for multiple comparisons by the Bonferroni method (eight exposures: P-value < 0.00625)., Main Results and the Role of Chance: In women, increases in genetically determined fasting insulin levels were associated with greater odds of infertility (+1 log(pmol/l): odds ratio 1.60, 95% CI 1.17 to 2.18, P-value = 0.003). The results were robust in the sensitivity analyses exploring the validity of MR assumptions and the role of pleiotropy of other cardiometabolic risk factors. There was also evidence of higher glucose and glycated hemoglobin causing infertility in women, but the findings were imprecise and did not pass our P-value threshold for multiple testing. The results for lipids and blood pressure were close to the null, suggesting that these did not cause infertility., Limitations, Reasons for Caution: We did not know if underlying causes of infertility were in the woman, man, or both. Our analyses only involved couples who had conceived. We did not have data on circulating levels of cardiometabolic risk factors, and we opted to conduct an MR analysis using GWAS summary statistics. No sex-specific genetic instruments on cardiometabolic risk factors were available. Our results may be affected by selection and misclassification bias. Finally, the characteristics of our study sample limit the generalizability of our results to populations of non-European ancestry., Wider Implications of the Findings: Treatments for lower fasting insulin levels may reduce the risk of infertility in women., Study Funding/competing Interest(s): The MoBa Cohort Study is supported by the Norwegian Ministry of Health and Care Services and the Norwegian Ministry of Education and Research. This work was supported by the European Research Council [grant numbers 947684, 101071773, 293574, 101021566], the Research Council of Norway [grant numbers 262700, 320656, 274611], the South-Eastern Norway Regional Health Authority [grant numbers 2020022, 2021045], and the British Heart Foundation [grant numbers CH/F/20/90003, AA/18/1/34219]. Open Access funding was provided by the Norwegian Institute of Public Health. The funders had no role in the study design; the collection, analysis, and interpretation of data; the writing of the report; or the decision to submit the article for publication. D.A.L. has received research support from National and International government and charitable bodies, Roche Diagnostics and Medtronic for research unrelated to the current work. O.A.A. has been a consultant to HealthLytix. The rest of the authors declare that no competing interests exist., Trial Registration Number: N/A., (© The Author(s) 2023. Published by Oxford University Press on behalf of European Society of Human Reproduction and Embryology.)

Maternal educational attainment (MEA) shapes offspring health through multiple potential pathways. Differential DNA methylation may provide a mechanistic understanding of these long-term associations. We aimed to quantify the associations of MEA with offspring DNA methylation levels at birth, in childhood and in adolescence. Using 37 studies from high-income countries, we performed meta-analysis of epigenome-wide association studies (EWAS) to quantify the associations of completed years of MEA at the time of pregnancy with offspring DNA methylation levels at birth (n = 9 881), in childhood (n = 2 017), and adolescence (n = 2 740), adjusting for relevant covariates. MEA was found to be associated with DNA methylation at 473 cytosine-phosphate-guanine sites at birth, one in childhood, and four in adolescence. We observed enrichment for findings from previous EWAS on maternal folate, vitamin-B 12 concentrations, maternal smoking, and pre-pregnancy BMI. The associations were directionally consistent with MEA being inversely associated with behaviours including smoking and BMI. Our findings form a bridge between socio-economic factors and biology and highlight potential pathways underlying effects of maternal education. The results broaden our understanding of bio-social associations linked to differential DNA methylation in multiple early stages of life. The data generated also offers an important resource to help a more precise understanding of the social determinants of health., (© 2023. The Author(s).)

Background: Smoking impacts DNA methylation, but data are lacking on smoking-related differential methylation by sex or dietary intake, recent smoking cessation (<1 year), persistence of differential methylation from in utero smoking exposure, and effects of environmental tobacco smoke (ETS)., Methods: We meta-analysed data from up to 15,014 adults across 5 cohorts with DNA methylation measured in blood using Illumina's EPIC array for current smoking (2560 exposed), quit < 1 year (500 exposed), in utero (286 exposed), and ETS exposure (676 exposed). We also evaluated the interaction of current smoking with sex or diet (fibre, folate, and vitamin C)., Findings: Using false discovery rate (FDR < 0.05), 65,857 CpGs were differentially methylated in relation to current smoking, 4025 with recent quitting, 594 with in utero exposure, and 6 with ETS. Most current smoking CpGs attenuated within a year of quitting. CpGs related to in utero exposure in adults were enriched for those previously observed in newborns. Differential methylation by current smoking at 4-71 CpGs may be modified by sex or dietary intake. Nearly half (35-50%) of differentially methylated CpGs on the 450 K array were associated with blood gene expression. Current smoking and in utero smoking CpGs implicated 3049 and 1067 druggable targets, including chemotherapy drugs., Interpretation: Many smoking-related methylation sites were identified with Illumina's EPIC array. Most signals revert to levels observed in never smokers within a year of cessation. Many in utero smoking CpGs persist into adulthood. Smoking-related druggable targets may provide insights into cancer treatment response and shared mechanisms across smoking-related diseases., Funding: Intramural Research Program of the National Institutes of Health, Norwegian Ministry of Health and Care Services and the Ministry of Education and Research, Chief Scientist Office of the Scottish Government Health Directorates and the Scottish Funding Council, Medical Research Council UK and the Wellcome Trust., Competing Interests: Declaration of interests DLM is a part-time employee of Optima Partners Ltd. ETGK received a grant from the Netherlands Lung Foundation. GHK received grants or contracts from ZON-MW, Vertex, Netherlands Lung Foundation, GSK, TEVA the Netherlands, and European Union; consulting fees from Astra Zeneca (money to institution); honoraria from Sanofi, Boehringer Ingelheim; and chairs the exquAlro Foundation. MCM received grants from the Research Council of Norway and European Research Council. REM is a scientific advisor to the Epigenetic Clock Development Foundation and Optima Partners. All other authors have nothing to disclose., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Background: Higher maternal pre-pregnancy body mass index (BMI) is associated with adverse pregnancy and perinatal outcomes. However, whether these associations are causal remains unclear., Methods: We explored the relation of maternal pre-/early-pregnancy BMI with 20 pregnancy and perinatal outcomes by integrating evidence from three different approaches (i.e. multivariable regression, Mendelian randomisation, and paternal negative control analyses), including data from over 400,000 women., Results: All three analytical approaches supported associations of higher maternal BMI with lower odds of maternal anaemia, delivering a small-for-gestational-age baby and initiating breastfeeding, but higher odds of hypertensive disorders of pregnancy, gestational hypertension, preeclampsia, gestational diabetes, pre-labour membrane rupture, induction of labour, caesarean section, large-for-gestational age, high birthweight, low Apgar score at 1 min, and neonatal intensive care unit admission. For example, higher maternal BMI was associated with higher risk of gestational hypertension in multivariable regression (OR = 1.67; 95% CI = 1.63, 1.70 per standard unit in BMI) and Mendelian randomisation (OR = 1.59; 95% CI = 1.38, 1.83), which was not seen for paternal BMI (OR = 1.01; 95% CI = 0.98, 1.04). Findings did not support a relation between maternal BMI and perinatal depression. For other outcomes, evidence was inconclusive due to inconsistencies across the applied approaches or substantial imprecision in effect estimates from Mendelian randomisation., Conclusions: Our findings support a causal role for maternal pre-/early-pregnancy BMI on 14 out of 20 adverse pregnancy and perinatal outcomes. Pre-conception interventions to support women maintaining a healthy BMI may reduce the burden of obstetric and neonatal complications., Funding: Medical Research Council, British Heart Foundation, European Research Council, National Institutes of Health, National Institute for Health Research, Research Council of Norway, Wellcome Trust., (© 2024. The Author(s).)

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., (© 2024. The Author(s).)

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., (© The Author(s) 2023. Published by Oxford University Press on behalf of European Society of Human Reproduction and Embryology.)

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/m 2 (95% CI 21.5, 23.5) among nulliparous women and 25.9 kg/m 2 (95% CI 24.1, 31.7) among multiparous women, with values of 20.4 kg/m 2 (20.0, 21.1) and 22.2 kg/m 2 (21.1, 24.3), respectively, for MPTB; for SPTB, the risk remained roughly largely constant above a BMI of around 25-30 kg/m 2 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., (© 2023. The Author(s).)

Circulating vitamin B12 concentrations during pregnancy are associated with offspring health. Foetal DNA methylation changes could underlie these associations. Within the Pregnancy And Childhood Epigenetics Consortium, we meta-analysed epigenome-wide associations of circulating vitamin B12 concentrations in mothers during pregnancy ( n  = 2,420) or cord blood ( n  = 1,029), with cord blood DNA methylation. Maternal and newborn vitamin B12 concentrations were associated with DNA methylation at 109 and 7 CpGs, respectively (False Discovery Rate P -value <0.05). Persistent associations with DNA methylation in the peripheral blood of up to 482 children aged 4-10 y were observed for 40.7% of CpGs associated with maternal vitamin B12 and 57.1% of CpGs associated with newborn vitamin B12. Of the CpGs identified in the maternal meta-analyses, 4.6% were associated with either birth weight or gestational age in a previous work. For the newborn meta-analysis, this was the case for 14.3% of the identified CpGs. Also, of the CpGs identified in the newborn meta-analysis, 14.3% and 28.6%, respectively, were associated with childhood cognitive skills and nonverbal IQ. Of the 109 CpGs associated with maternal vitamin B12, 18.3% were associated with nearby gene expression. In this study, we showed that maternal and newborn vitamin B12 concentrations are associated with DNA methylation at multiple CpGs in offspring blood ( P FDR <0.05). Whether this differential DNA methylation underlies associations of vitamin B12 concentrations with child health outcomes, such as birth weight, gestational age, and childhood cognition, should be further examined in future studies.

Prenatal maternal stressful life events are associated with adverse neurodevelopmental outcomes in offspring. Biological mechanisms underlying these associations are largely unknown, but DNA methylation likely plays a role. This meta-analysis included twelve non-overlapping cohorts from ten independent longitudinal studies (N = 5,496) within the international Pregnancy and Childhood Epigenetics consortium to examine maternal stressful life events during pregnancy and DNA methylation in cord blood. Children whose mothers reported higher levels of cumulative maternal stressful life events during pregnancy exhibited differential methylation of cg26579032 in ALKBH3. Stressor-specific domains of conflict with family/friends, abuse (physical, sexual, and emotional), and death of a close friend/relative were also associated with differential methylation of CpGs in APTX, MyD88, and both UHRF1 and SDCCAG8, respectively; these genes are implicated in neurodegeneration, immune and cellular functions, regulation of global methylation levels, metabolism, and schizophrenia risk. Thus, differences in DNA methylation at these loci may provide novel insights into potential mechanisms of neurodevelopment in offspring., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Background: Prenatal caffeine exposure may influence offspring health via DNA methylation, but no large studies have tested this. Materials & methods: Epigenome-wide association studies and differentially methylated regions in cord blood (450k or EPIC Illumina arrays) were meta-analyzed across six European cohorts (n = 3725). Differential methylation related to self-reported caffeine intake (mg/day) from coffee, tea and cola was compared with assess whether caffeine is driving effects. Results: One CpG site (cg19370043, PRRX1 ) was associated with caffeine and another (cg14591243, STAG1 ) with cola intake. A total of 12-22 differentially methylated regions were detected with limited overlap across caffeinated beverages. Conclusion: We found little evidence to support an intrauterine effect of caffeine on offspring DNA methylation. Statistical power limitations may have impacted our findings.

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., (© 2023. BioMed Central Ltd., part of Springer Nature.)

Infertility is a heterogeneous phenotype, and for many couples, the causes of fertility problems remain unknown. One understudied hypothesis is that allelic interactions between the genotypes of the two parents may influence the risk of infertility. Our aim was, therefore, to investigate how allelic interactions can be modeled using parental genotype data linked to 15,789 pregnancies selected from the Norwegian Mother, Father, and Child Cohort Study. The newborns in 1304 of these pregnancies were conceived using assisted reproductive technologies (ART), and the remainder were conceived naturally. Treating the use of ART as a proxy for infertility, different parameterizations were implemented in a genome-wide screen for interaction effects between maternal and paternal alleles at the same locus. Some of the models were more similar in the way they were parameterized, and some produced similar results when implemented on a genome-wide scale. The results showed near-significant interaction effects in genes relevant to the phenotype under study, such as Dynein axonemal heavy chain 17 (DNAH17) with a recognized role in male infertility. More generally, the interaction models presented here are readily adaptable to the study of other phenotypes in which maternal and paternal allelic interactions are likely to be involved., (© 2023 The Authors. Genetic Epidemiology published by Wiley Periodicals LLC.)

Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.