BackgroundPregnancy requires a delicate balance between the maternal immune system and inflammatory responses. Elevated maternal body mass index (BMI) significantly compromises the immune system and increases systemic inflammation. High maternal BMI is associated with adverse pregnancy outcomes, including an increased risk of both pre-eclampsia and preterm birth, which may be mediated through immune-related blood cell changes.MethodsThis study used Mendelian randomisation (MR) to investigate the causal relationship between maternal BMI and pregnancy outcomes, including birth weight, placental weight, gestational duration, and pre-eclampsia. We applied two-step MR to assess whether immune-related blood counts, such as neutrophils, lymphocytes, and platelets, mediate these relationships. Single-nucleotide polymorphism (SNP) effect estimates for maternal BMI and pregnancy outcomes were sourced from publicly available genome-wide association studies (GWASs), with pregnancy outcomes partitioned into maternal genetic effects to proxy genetic effects on the intrauterine environment.ResultsWe found that elevated maternal BMI causally increased placental weight (βIVW = 0.164 standard deviation (SD) increase in placental weight per SD increase in maternal BMI, p = 2.92 × 10−7) and the risk of pre-eclampsia (ORiVW 1.75, p = 6.3 × 10−30). The effect of maternal BMI on placental weight was larger than its effect on birth weight. Mediation analysis found no evidence of the involvement of immune-related blood counts in these relationships.ConclusionMaternal BMI has a significant impact on pregnancy outcomes, particularly by increasing placental weight and the risk of pre-eclampsia. These findings highlight BMI-driven placental adaptations as key contributors to pregnancy complications.

Despite significant advances in pre- and postnatal care over the last century, adverse pregnancy related events still occur frequently. We used Mendelian randomisation (MR) to investigate potential causal effects of the mother’s and fetal blood proteome on pregnancy related outcomes including birthweight, placental weight, preeclampsia, and sporadic miscarriage. We generated a list of genetic instruments to act as proxies for plasma proteins by combining two recent large protein GWAS (4719 proteins N = 35,559 individuals; 4775 proteins N = 10,708 individuals). We identified 1724 proteins with valid cis-pQTLs for use as genetic instruments. We identified evidence for causal relationships (MR Bonferroni corrected pBonferroni < 2.90 × 10−5) involving fetal effects and/or maternal effects on birthweight and preeclampsia. Increased levels of PSG7 and BCMA and decreased levels of VLCAD, INHBB, and PLCG1 in the fetal circulation were potentially causal for increased birthweight. Similarly, increased levels of LIMA1 and decreased levels of VLCAD, FBLN3, and galectin-4 in the maternal circulation were potentially causal for increased birthweight. Decreased levels of SERPINE2 and SIGLEC6 were potentially causal for increased risk of preeclampsia. We did not find any significant effects of proxied maternal or fetal proteins on placental weight or sporadic miscarriage, perhaps due to the smaller size of their GWAS meta-analyses. Our results implicate several proteins that may be involved in the aetiology of perinatal phenotypes that will need to be replicated in independent datasets.

IntroductionPreterm delivery risk is increased for women with a previous cesarean section, which are becoming more common worldwide. However, this risk is based on studies which have not fully accounted for selection bias, and the studied outcomes have been limited to the study of early deliveries. This study aimed to determine the impact of previous delivery modes on the incidence of deviant duration of subsequent pregnancies.Material and methodsThis retrospective cohort study used clinical data registered in the Swedish Medical Birth Register. 612 935 women with their first two pregnancies and 157 581 women with their first three pregnancies were included. The outcome was the gestational duration of the last pregnancy of the series, depending on previous delivery modes. The associations were analysed with multivariable logistic regression (with the gestational duration categorised) and survival models including Cox regression analyses.ResultsWhen using standard logistic regression, previous cesarean section was associated with an increased risk of both spontaneous preterm birth (adjusted odds ratio [aOR] 1.67, 95% CI 1.57-1.77) and postterm birth (aOR 1.55, 95% CI 1.49-1.62). However, the more appropriate survival models only showed an association between cesarean section and longer gestational duration of the subsequent pregnancy (adjusted hazard ratio 0.72, 95% CI 0.71-0.73).ConclusionsThe survival model handles bias related to management differences between the exposure and reference groups better than standard logistic regression, making it the statistical method of choice when conducting studies on this research topic. This study shows that the main association between cesarean section and the gestational duration of the subsequent pregnancy is the prolonging of it, which stands in contrast with previous research on the topic.

Early childhood obesity is a growing global concern; however, the role of common genetic variation on infant and child weight development is unclear. Here, we identify 46 loci associated with early childhood body mass index at specific ages, matching different child growth phases, and representing four major trajectory patterns. We perform genome-wide association studies across 12 time points from birth to 8 years in 28,681 children and their parents (27,088 mothers and 26,239 fathers) in the Norwegian Mother, Father and Child Cohort Study. Monogenic obesity genes are overrepresented near identified loci, and several complex association signals near LEPR, GLP1R, PCSK1 and KLF14 point towards a major influence for common variation affecting the leptin–melanocortin system in early life, providing a link to putative treatment strategies. We also demonstrate how different polygenic risk scores transition from birth to adult profiles through early child growth. In conclusion, our results offer a fine-grained characterization of a changing genetic landscape sustaining early childhood growth. Helgeland et al. characterize genetic loci associated with early childhood body mass index, highlighting roles of genes involved in monogenic obesity, appetite regulation and energy expenditure, many of which show age-specific association patterns.

Bleeding in early pregnancy and postpartum hemorrhage (PPH) bear substantial risks, with the former closely associated with pregnancy loss and the latter being the foremost cause of maternal death, underscoring the severe impact on maternal-fetal health. We identified five genetic loci linked to PPH in a meta-analysis. Functional annotation analysis indicated candidate genes HAND2, TBX3 and RAP2C/FRMD7 at three loci and showed that at each locus, associated variants were located within binding sites for progesterone receptors. There were strong genetic correlations with birth weight, gestational duration and uterine fibroids. Bleeding in early pregnancy yielded no genome-wide association signals but showed strong genetic correlation with various human traits, suggesting a potentially complex, polygenic etiology. Our results suggest that PPH is related to progesterone signaling dysregulation, whereas early bleeding is a complex trait associated with underlying health and possibly socioeconomic status and may include genetic factors that have not yet been identified.

ObjectiveEndometriosis affects 10% of women worldwide and is linked to adverse pregnancy outcomes, including preterm birth. Recent epidemiological and genetic studies indicate that endometriosis may influence gestational duration and the likelihood of preterm birth. This study aimed to estimate the direct genetic causal effects of endometriosis on gestational duration and preterm birth using Mendelian randomisation (MR) analysis, leveraging genetic data from recent genome-wide association studies (GWASs).DesignA two-sample MR study.SettingSummary statistics from published GWASs on European ancestry populations for endometriosis and gestational duration.Population or SampleInstrumental variables for endometriosis were derived from a meta-analysis comprising 60 674 endometriosis cases and 701 926 controls.MethodsGenetic correlations and heritability estimates were calculated using linkage disequilibrium score regression. Two-sample MR with multiplicative random-effects inverse variance weighting assessed the primary objectives, supplemented by sensitivity analyses to validate MR assumptions.Main Outcome MeasuresPrimary outcomes were gestational duration and preterm birth, sourced from the latest GWAS data.ResultsLD score regression revealed no genetic correlation between endometriosis and either gestational duration or preterm birth. MR analysis showed no causal association between endometriosis and maternal effects on offspring gestational duration (beta = 0.40, 95% CI: -0.39 to 1.19, p = 0.32) or preterm birth (OR = 0.94, 95% CI: 0.82-1.06, p = 0.36). Sensitivity analyses indicated pleiotropy but no violations of MR assumptions. Of the four loci overlapping between the gestational duration and endometriosis GWASs, three (EBF1, WNT4, and GDAP1) were identified as outliers using MR-Presso.ConclusionsContrary to observational studies, MR analyses found no direct causal link between endometriosis and gestational duration or preterm birth. Overlaps in genomic regions suggest that the relationship may be mediated through different biological pathways.

Jaundice affects almost all neonates in their first days of life and is caused by the accumulation of bilirubin. Although the core biochemistry of bilirubin metabolism is well understood, it is not clear why some neonates experience more severe jaundice and require treatment with phototherapy. Here, we present the first genome-wide association study of neonatal jaundice to date in nearly 30,000 parent-offspring trios from Norway (cases ≈ 2000). The alternate allele of a common missense variant affecting the sequence of UGT1A4 reduces the susceptibility to jaundice five-fold, which replicated in separate cohorts of neonates of African American and European ancestries. eQTL colocalization analyses indicate that the association may be driven by regulation of UGT1A1 in the intestines, but not in the liver. Our results reveal marked differences in the genetic variants involved in neonatal jaundice compared to those regulating bilirubin levels in adults, suggesting distinct genetic mechanisms for the same biological pathways.

The timing of parturition is crucial for neonatal survival and infant health. Yet, its genetic basis remains largely unresolved. We present a maternal genome-wide meta-analysis of gestational duration ( n = 195,555), identifying 22 associated loci (24 independent variants) and an enrichment in genes differentially expressed during labor. A meta-analysis of preterm delivery (18,797 cases, 260,246 controls) revealed seven associated loci and large genetic similarities with gestational duration. Analysis of the parental transmitted and nontransmitted alleles ( n = 136,833) shows that 15 of the gestational duration genetic variants act through the maternal genome, whereas 7 act both through the maternal and fetal genomes and 2 act only via the fetal genome. Finally, the maternal effects on gestational duration show signs of antagonistic pleiotropy with the fetal effects on birth weight: maternal alleles that increase gestational duration have negative fetal effects on birth weight. The present study provides insights into the genetic effects on the timing of parturition and the complex maternal–fetal relationship between gestational duration and birth weight.

Background:While polygenic risk scores hold significant promise in estimating an individual's risk of developing a complex trait such as obesity, their application in the clinic has, to date, been limited by a lack of data from non-European populations. As a collaboration model of the International Hundred K+ Cohorts Consortium (IHCC), we endeavored to develop a globally applicable trans-ethnic PRS for body mass index (BMI) through this relatively new international effort. Methods:The PRS model was developed trained and tested at the Center for Applied Genomics (CAG) of The Children's Hospital of Philadelphia (CHOP) based on a BMI meta-analysis from the GIANT consortium. The validated PRS models were subsequently disseminated to the participating sites. Scores were generated by each site locally on their cohorts and summary statistics returned to CAG for final analysis. Results:We show that in the absence of a well powered trans-ethnic GWAS from which to derive SNPs and effect estimates, trans-ethnic scores can be generated from European ancestry GWAS using Bayesian approaches such as LDpred to adjust the summary statistics using trans-ethnic linkage disequilibrium reference panels. The ported trans-ethnic scores outperform population specific-PRS across all non-European ancestry populations investigated including East Asians and three-way admixed Brazilian cohort. Conclusions:Widespread use of PRS in the clinic is hampered by a lack of genotyping data in individuals of non-European ancestry for the vast majority of traits. Here we show that for a truly polygenic trait such as BMI adjusting the summary statistics of a well powered European ancestry study using trans-ethnic LD reference results in a score that is predictive across a range of ancestries including East Asians and three-way admixed Brazilians.

Delivering preterm is the leading cause of death in neonates and children under five years of age. Both genetics and environmental factors play a role in timing of delivery, and these influences can be unique to a single pregnancy or shared across pregnancies of the same mother. The aim of this study was to understand how gestational duration is affected by parity and how parity modifies the association between history of preterm delivery and gestational duration. To investigate this, we analysed 1 118 318 spontaneous deliveries (1990 - 2012) from the Swedish Medical Birth Register, with access to pedigrees, using linear regressions and linear mixed models. We found that parity has a modest effect on the mean and a large effect on the variance of gestational duration. Interactions with a woman's clinical and family history of preterm delivery revealed both pregnancy-specific and shared factors. For instance, the effect of a previous preterm delivery on gestational duration is present across pregnancies, but the magnitude of its effect is pregnancy specific. The access to pedigrees made it possible to apply linear mixed models, thus including all woman's pregnancies in the model and accounting for unobserved mother-specific covariates. The linear mixed models highlighted a group effect bias when using linear regression to estimate the association between parity and gestational duration, likely caused by socioeconomic factors. Our study shed light on how parity affects gestational duration and modifies the effect of well-known risk factors of preterm delivery.

A well-functioning placenta is essential for fetal and maternal health throughout pregnancy. Using placental weight as a proxy for placental growth, we report genome-wide association analyses in the fetal ( n = 65,405), maternal ( n = 61,228) and paternal ( n = 52,392) genomes, yielding 40 independent association signals. Twenty-six signals are classified as fetal, four maternal and three fetal and maternal. A maternal parent-of-origin effect is seen near KCNQ1 . Genetic correlation and colocalization analyses reveal overlap with birth weight genetics, but 12 loci are classified as predominantly or only affecting placental weight, with connections to placental development and morphology, and transport of antibodies and amino acids. Mendelian randomization analyses indicate that fetal genetically mediated higher placental weight is causally associated with preeclampsia risk and shorter gestational duration. Moreover, these analyses support the role of fetal insulin in regulating placental weight, providing a key link between fetal and placental growth.

Preterm birth is a major burden to neonatal health worldwide, determined in part by genetics. Recently, studies discovered several genes associated with this trait or its continuous equivalent - gestational duration. However, their effect timing, and thus clinical importance, is still unclear. Here, we use genotyping data of 31,000 births from the Norwegian Mother, Father and Child cohort (MoBa) to investigate different models of the genetic pregnancy "clock". We conduct genome-wide association studies using gestational duration or preterm birth, replicating known maternal associations and finding one new foetal variant. We illustrate how the interpretation of these results is complicated by the loss of power when dichotomizing. Using flexible survival models, we resolve this complexity and find that many of the known loci have time-varying effects, often stronger early in pregnancy. The overall polygenic control of birth timing appears to be shared in the term and preterm, but not very preterm periods, and exploratory results suggest involvement of the major histocompatibility complex genes in the latter. These findings show that the known gestational duration loci are clinically relevant, and should help design further experimental studies.

Atopic dermatitis (AD) is a common inflammatory skin condition and prior genome-wide association studies (GWAS) have identified 71 associated loci. In the current study we conducted the largest AD GWAS to date (discovery N = 1,086,394, replication N = 3,604,027), combining previously reported cohorts with additional available data. We identified 81 loci (29 novel) in the European-only analysis (which all replicated in a separate European analysis) and 10 additional loci in the multi-ancestry analysis (3 novel). Eight variants from the multi-ancestry analysis replicated in at least one of the populations tested (European, Latino or African), while two may be specific to individuals of Japanese ancestry. AD loci showed enrichment for DNAse I hypersensitivity and eQTL associations in blood. At each locus we prioritised candidate genes by integrating multi-omic data. The implicated genes are predominantly in immune pathways of relevance to atopic inflammation and some offer drug repurposing opportunities.

Bleeding in early pregnancy and postpartum hemorrhage (PPH) bear substantial risks, with the former closely associated with pregnancy loss and the latter being the foremost cause of maternal death, underscoring the severity of these complications in maternal-fetal health. Here, we investigated the genetic variation underlying aspects of pregnancy-associated bleeding and identified five loci associated with PPH through a meta-analysis of 21,512 cases and 259,500 controls. Functional annotation analysis indicated candidate genes, HAND2, TBX3, and RAP2C/FRMD7, at three loci and showed that at each locus, associated variants were located within binding sites for progesterone receptors (PGR). Furthermore, there were strong genetic correlations with birth weight, gestational duration, and uterine fibroids. Early bleeding during pregnancy (28,898 cases and 302,894 controls) yielded no genome-wide association signals, but showed strong genetic correlation with a variety of human traits, indicative of polygenic and pleiotropic effects. Our results suggest that postpartum bleeding is related to myometrium dysregulation, whereas early bleeding is a complex trait related to underlying health and possibly socioeconomic status.

Purpose: Preterm delivery is a major cause of child mortality. While the relationship between parity and preterm delivery is known, its association with gestational duration and variability remains underexplored. Differences in variance may suggest interaction with other well-established risk factors.Methods: With 1.1 million spontaneous deliveries (1990-2012) from the Swedish Medical Birth Register, we assessed while accounting for potential confounders the effects of parity on the mean and variance of gestational duration, and its possible interactions with history of preterm delivery. Pedigrees allowed to account for nonobserved, shared confounders using linear mixed models. Results: Parity has a modest association with mean gestational duration, but a large effect on its variance. For example, the first pregnancy had the shortest mean gestational duration, 0.29 days shorter (95% CI: -0.33, -0.25) than the second, and the largest variance (sigma 2 = 135 days2). Accounting for shared unobserved confounders highlighted a group effect bias, likely linked to the mothers' total number of offspring. Parity interacts with other risk factors, including previous preterm delivery where the magnitude of its effect increases with parity (up to 4.6 days effect difference).Conclusions: Nonshared factors across a mother's pregnancies highlight parity's importance to gain insight into the mechanisms governing the timing of delivery.(c) 2023 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

A well-functioning placenta is essential for fetal and maternal health throughout pregnancy. Using placental weight after term delivery as a proxy for placental growth, we report genome-wide association analyses in the fetal ( n = 65,405), maternal ( n = 61,228), and paternal ( n = 52,392) genomes, yielding 40 independent association signals. Twenty-six signals are confidently classified as fetal only, four maternal only, and three fetal and maternal. A maternal parent-of-origin effect is seen near KCNQ1 . Genetic correlation and colocalization analyses reveal overlap with birth weight genetics, but twelve loci are classified as predominantly or only affecting placental weight, with connections to placental development and morphology, and transport of antibodies and amino acids. Mendelian randomization analyses indicate that fetal genetically mediated higher placental weight is causally associated with risk of preeclampsia or shorter gestational duration. Moreover, these analyses support a role for insulin produced by the fetus in regulating the growth of the placenta, providing a key link between fetal and placental growth.

Background C-reactive protein (CRP) is an acute-phase marker of inflammation. Previous epidemiological studies have associated elevated maternal CRP levels during pregnancy with preterm birth risk and lower birth weight. However, the causal relationships behind these observed associations are not clear. Methods and Findings We utilized phenotype and genotype data on 10,734 mother/child pairs of European ancestry collected from six birth cohorts. We performed two-sample multivariate Mendelian Randomization (MR) using maternal non-transmitted alleles to interrogate the causal effect of maternal CRP on gestational duration and birth weight. Based on the non-transmitted alleles of 55 CRP associated single nucleotide polymorphisms (SNPs), a unit increase in log-transformed maternal CRP level was associated with a reduction of 1.58 days (95% CI: 0.23, 2.94, P = 0.022) in gestational duration and a reduction of 76.3g (95% CI: 18.2, 134.4, P = 0.010) in birth weight. The magnitude of the association between genetically increased CRP and birth weight was reduced after adjusting for gestational age. Utilizing the effect estimates of CRP-associated SNPs on birth weight from the UK Biobank genome-wide association (GWA) summary results, our results suggested one unit of genetically increased maternal CRP was associated with a decrease of 50.1g (95% CI: 24.7, 75.5, P = 9.6E-5) of birth weight (unadjusted by gestational age). We validated the results using a single genetic variant (rs2794520) near the CRP gene, which is less prone to horizontal pleiotropy bias. Conclusions Increased maternal CRP levels appear to causally reduce gestational duration and birth weight. The effect of maternal CRP on birth weight is partially due to its effect on gestational duration. The estimated causal effect sizes are consistent with previous epidemiological reports and this triangulation increases confidence in these results being causal.

To elucidate the role of common genetic variation on infant and child weight development, we performed genome-wide association studies across 12 time points from birth to eight years in 28,681 children and their parents (27,088 mothers and 26,239 fathers) in the Norwegian Mother, Father and Child Cohort Study (MoBa). We identify 46 distinct loci associated with early childhood BMI at specific ages, matching different child growth phases, and representing four major trajectory patterns. Among these loci, 30 are independent of known birth weight and adult BMI loci, and 21 show peak effect between six months and three years, making these discoverable only at early age. Several of the 21 variants reside in/near genes previously implicated in severe forms of early-onset obesity, and monogenic obesity genes are enriched in the vicinity of the 46 loci. Four loci demonstrate evidence of several independent association signals as key drivers for BMI development near LEPR, GLP1R, PCSK1 , and KLF14 , all central to appetite and energy balance. At the KLF14 locus, we detect significant associations for maternally inherited alleles only, consistent with imprinting effects. Finally, we demonstrate how the BMI distribution stratified by different polygenic risk scores transitions from birth to adult profile throughout early childhood, and how age-specific polygenic risk scores improve the prediction of childhood obesity, outperforming scores based on adult BMI. In conclusion, our results offer a fine-grained characterization of the rapidly changing genetic association landscape sustaining early growth.