Assessing the Causal Relationship of Maternal Height on Birth Size and Gestational Age at Birth: A Mendelian Randomization Analysis

Maternal height, and ethnicity and birth weight: A retrospective cohort study of uncomplicated term vaginal deliveries in Malaysia

BACKGROUND

Small for gestational age (SGA) and large for gestational age (LGA) are designations given to neonates based solely on birthweight, with no distinction made for maternal height. However, there is a possibility that maternal height is significantly correlated with neonatal birthweight, and if so, SGA and LGA cutoffs specific to maternal height may be a more precise and useful tool for clinicians. To explore this possibility, we analyzed the association between maternal height and ethnicity and neonate birthweight in women with low-risk, 37- to 40-week gestation, singleton pregnancies who gave birth vaginally between 2010 and 2017 (n = 354,488). For this retrospective cohort study, we used electronic obstetric records obtained from the National Obstetrics Registry in Malaysia.

METHODS

National Obstetric Registry (NOR) data were used to calculate the 10th and 90th birthweight percentiles for each maternal height group by gestational age and neonatal sex. Multiple linear regression models, adjusted for maternal age, weight, parity, gestational age, and neonatal sex, were used to examine the association between neonate birthweight and maternal ethnicity and height. The following main outcome measures were assessed: small for gestational age (<10th percentile), large for gestational age (>90th percentile), and birthweight.

RESULTS

The median height was 155 cm (IQR, 152-159), with mothers of Chinese descent being the tallest (median (IQR): 158 cm (154-162)) and mothers of Orang Asli (Indigenous) descent the shortest (median (IQR): 151 cm (147-155)). The median birthweight was 3000 g (IQR, 2740-3250), with mothers of Malay and Chinese ethnicity and Others having, on average, the heaviest babies, followed by other Bumiputeras (indigenous) mothers, mothers of Indian ethnicity, and lastly, mothers of Orang Asli ethnicity. For infants, maternal age, height, weight, parity, male sex, and gestational age were positively associated with birthweight. Maternal height had a positive association with neonate birthweight (B = 7.08, 95% CI: 6.85-7.31). For ethnicity, compared with neonates of Malay ethnicity, neonates of Chinese, Indian, Orang Asli, and other Bumiputera ethnicities had lower birthweights.

CONCLUSION

Birthweight increases with maternal height among Malaysians of all ethnicities. SGA and LGA cutoffs specific to maternal height may be useful to guide pregnancy management.

Recent Advances in Genomic Studies of Gestational Duration and Preterm Birth

Preterm birth (PTB) is the leading cause of infant mortality and morbidity. For several decades, extensive epidemiologic and genetic studies have highlighted the significant contribution of maternal and offspring genetic factors to PTB. This review discusses the challenges inherent in conventional genomic analyses of PTB and underscores the importance of adopting nonconventional approaches, such as analyzing the mother-child pair as a single analytical unit, to disentangle the intertwined maternal and fetal genetic influences. We elaborate on studies investigating PTB phenotypes through 3 levels of genetic analyses: single-variant, multi-variant, and genome-wide variants.

Stunting predictors among children aged 0-24 months in Southeast Asia: a scoping review

OBJECTIVE

To identify predictors of stunting among children 0-24 months in Southeast Asia.

METHODS

This scoping review focused on articles with observational study design in English published from 2012 to 2023 from five international databases. The primary keyword used were: "stunting" OR "growth disorder" AND "newborn" AND "predict" AND "Southeast Asia".

RESULTS

Of the 27 articles selected for the final analysis there are thirteen predictors of stunting in seven Southeast Asia countries. The thirteen predictors include the child, mother, home, inadequate complementary feeding, inadequate breastfeeding, inadequate care, poor quality foods, food and water safety, infection, political economy, health and healthcare, water, sanitation, and environment, and social culture factor.

CONCLUSION

All these predictors can lead to stunting in Southeast Asia. To prevent it, health service providers and other related sectors need to carry out health promotion and health prevention according to the predictors found.

Methodological approaches, challenges, and opportunities in the application of Mendelian randomisation to lifecourse epidemiology: A systematic literature review

Diseases diagnosed in adulthood may have antecedents throughout (including prenatal) life. Gaining a better understanding of how exposures at different stages in the lifecourse influence health outcomes is key to elucidating the potential benefits of disease prevention strategies. Mendelian randomisation (MR) is increasingly used to estimate causal effects of exposures across the lifecourse on later life outcomes. This systematic literature review explores MR methods used to perform lifecourse investigations and reviews previous work that has utilised MR to elucidate the effects of factors acting at different stages of the lifecourse. We conducted searches in PubMed, Embase, Medline and MedRXiv databases. Thirteen methodological studies were identified. Four studies focused on the impact of time-varying exposures in the interpretation of "standard" MR techniques, five presented methods for repeat measures of the same exposure, and four described methodological approaches to handling multigenerational exposures. A further 127 studies presented the results of an applied research question. Over half of these estimated effects in a single generation and were largely confined to the exploration of questions regarding body composition. The remaining mostly estimated maternal effects. There is a growing body of research focused on the development and application of MR methods to address lifecourse research questions. The underlying assumptions require careful consideration and the interpretation of results rely on select conditions. Whilst we do not advocate for a particular strategy, we encourage practitioners to make informed decisions on how to approach a research question in this field with a solid understanding of the limitations present and how these may be affected by the research question, modelling approach, instrument selection, and data availability.

Influence of maternal and neonatal continuum of care on the risk of intergenerational cycle of stunting: a cross-sectional study

OBJECTIVES

This study aimed to analyse the influence of the continuum of care during pregnancy and neonatal periods on the risk of intergenerational cycle of stunting.

DESIGN

This study was a cross-sectional study, with data analysed from the 2018 Basic Health Research in Indonesia.

SETTINGS

Basic Health Research 2018 was conducted throughout 513 cities/regencies in 34 provinces in Indonesia. The households were selected through two-stage sampling methods. First, census blocks (CB) were selected using probability proportional to size methods in each urban/rural stratum from each city/regency. Ten households were then selected from each CB using systematic sampling methods. All family members of the selected households were measured and interviewed.

PARTICIPANTS

This study analyses 31 603 children aged 0-24 months.

OUTCOMES MEASURES

The dependent variable was the risk of the intergenerational cycle of stunting. Mothers who had a height less than 150.1 cm (short stature mothers) and had children (≤ 24 months of age) with length-for-age Z-score less than -2 Standard Deviation (SD) of the WHO Child Growth Standard (stunted children) were defined as at risk of the intergenerational cycle of stunting.

RESULTS

Mothers with incomplete maternal and neonatal care visits were 30% more likely to be at risk on the intergenerational cycle of stunting (OR (95% CI): 1.3 (1.00 to 1.63)) after adjusting for economic status.

CONCLUSION

The continuum of maternal and neonatal healthcare visits could potentially break the intergenerational cycle of stunting, especially in populations where stunted mothers are prevalent.

Disentangling the link between maternal influences on birth weight and disease risk in 36,211 genotyped mother-child pairs

Epidemiological studies have robustly linked lower birth weight to later-life disease risks. These observations may reflect the adverse impact of intrauterine growth restriction on a child's health. However, causal evidence supporting such a mechanism in humans is largely lacking. Using Mendelian Randomization and 36,211 genotyped mother-child pairs from the FinnGen study, we assessed the relationship between intrauterine growth and five common health outcomes (coronary heart disease (CHD), hypertension, statin use, type 2 diabetes and cancer). We proxied intrauterine growth with polygenic scores for maternal effects on birth weight and took into account the transmission of genetic variants between a mother and a child in the analyses. We find limited evidence for contribution of normal variation in maternally influenced intrauterine growth on later-life disease. Instead, we find support for genetic pleiotropy in the fetal genome linking birth weight to CHD and hypertension. Our study illustrates the opportunities that data from genotyped parent-child pairs from a population-based biobank provides for addressing causality of maternal influences.

Reconsidering the developmental origins of adult disease paradigm: The 'metabolic coordination of childbirth' hypothesis

In uncomplicated pregnancies, birthweight is inversely associated with adult non-communicable disease (NCD) risk. One proposed mechanism is maternal malnutrition during pregnancy. Another explanation is that shared genes link birthweight with NCDs. Both hypotheses are supported, but evolutionary perspectives address only the environmental pathway. We propose that genetic and environmental associations of birthweight with NCD risk reflect coordinated regulatory systems between mother and foetus, that evolved to reduce risks of obstructed labour. First, the foetus must tailor its growth to maternal metabolic signals, as it cannot predict the size of the birth canal from its own genome. Second, we predict that maternal alleles that promote placental nutrient supply have been selected to constrain foetal growth and gestation length when fetally expressed. Conversely, maternal alleles that increase birth canal size have been selected to promote foetal growth and gestation when fetally expressed. Evidence supports these hypotheses. These regulatory mechanisms may have undergone powerful selection as hominin neonates evolved larger size and encephalisation, since every mother is at risk of gestating a baby excessively for her pelvis. Our perspective can explain the inverse association of birthweight with NCD risk across most of the birthweight range: any constraint of birthweight, through plastic or genetic mechanisms, may reduce the capacity for homeostasis and increase NCD susceptibility. However, maternal obesity and diabetes can overwhelm this coordination system, challenging vaginal delivery while increasing offspring NCD risk. We argue that selection on viable vaginal delivery played an over-arching role in shaping the association of birthweight with NCD risk.

Higher risk of preterm twin delivery among shorter nulliparous women

OBJECTIVE

To determine if maternal height in nulliparous women influences pregnancy results in twin pregnancies.

MATERIAL AND METHODS

Retrospective cohort analysis evaluating twin pregnancies followed at Centro Hospitalar Universitário Lisboa Central, between 1995 and 2020. Of the 2900 pregnancies followed in that period, 886 nulliparous women with dichorionic twin pregnancies were selected. Two groups were considered: A - maternal height <163 cm (

RESULT(S)

PTB rates decreased along increasing maternal height. The comparison between group A and group B revealed no statistically significant differences in maternal characteristics (age, mode of conception - spontaneous or ART pregnancies, or BMI). Statistically significant differences were found in mean gestational age at birth (35.1 ± 1.8 vs. 36.0 ± 2.6 wks), PTB rates < 32, 34 and 36 wks, OR: 3.2, 2.3 and 2.4 respectively, p < 0.01. Shorter women had a 1.7× and 2.6× increased risk for significantly low (<2500 g) and very low (<1500 g) newborn birth weight (BW), respectively, and a 40 % increased risk of Cesarian delivery. No significant differences were shown with respect to stillbirths, neonatal and perinatal deaths, which had a low incidence in this study. In ART pregnancies we found the same results regarding PTB rates and newborn birthweight in shorter women. In Logistic Regression analysis, maternal height

CONCLUSION

Increased pregnancy risk in nulliparous shorter women should be taken into consideration in double embryo transfers.

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Key Words

• Art
• Dichorionic twins
• Maternal height
• Nulliparous women
• Perinatal outcomes

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MESH Headings

• Pregnancy
• Infant, Newborn
• Female
• Humans
• Infant
• Pregnancy, Twin
• Stillbirth
• Retrospective Studies
• Cesarean Section/adverse effects
• Premature Birth/epidemiology
• Infant, Very Low Birth Weight
• Birth Weight

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Affiliation(s)

Teresinha Simões Department of Maternal-Fetal Medicine, Maternity Dr. Alfredo da Costa, Centro Hospitalar Lisboa Central and Nova Medical School, Lisbon, Portugal; Department of Reproductive Medicine, Maternity Dr. Alfredo da Costa, Centro Hospitalar Lisboa Central and Nova Medical School, Lisbon, Portugal.
Inês Pereira Department of Maternal-Fetal Medicine, Maternity Dr. Alfredo da Costa, Centro Hospitalar Lisboa Central, Lisbon, Portugal
Laura Gomes Department of Maternal-Fetal Medicine, Maternity Dr. Alfredo da Costa, Centro Hospitalar Lisboa Central, Lisbon, Portugal
Sofia Brás Department of Maternal-Fetal Medicine, Maternity Dr. Alfredo da Costa, Centro Hospitalar Lisboa Central, Lisbon, Portugal
Isabel Nogueira Department of Maternal-Fetal Medicine, Maternity Dr. Alfredo da Costa, Centro Hospitalar Lisboa Central, Lisbon, Portugal
Alexandra Queirós Department of Maternal-Fetal Medicine, Prenatal Diagnosis Unit Maternity Dr. Alfredo da Costa, Centro Hospitalar Lisboa Central and Nova Medical School, Lisbon, Portugal

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The Association Between Maternal Short Stature and Neonatal Intensive Care Unit Admission: A Longitudinal Study in Sabah

BACKGROUND

The rising number of newborns requiring neonatal intensive care unit (NICU) care poses immediate threats to their health and places emotional and financial burdens on families and healthcare systems. This study investigates the direct effect of maternal short stature on NICU admission in Sabah, Malaysia.

METHODS

A longitudinal study at Hospital Wanita Dan Kanak-Kanak Sabah (HWKKS) from 2018 to 2022 included 254 Malaysian women with singleton pregnancies and neonates born after the 37th week, excluding significant disorders, smoking/alcohol use, fetal death, and malformations. Birth weight, gestational age, and neonatal condition were recorded. The association between maternal height, low birth weight (LBW), and NICU admission was analyzed.

RESULTS

LBW prevalence was 15.35%, with an average participant height of 147.37 cm. Maternal stature was significantly associated with LBW, with the shortest quartile (Q1) having the highest risk. LBW was significantly associated with NICU admission, with LBW newborns at a sixfold higher risk. Maternal height was also significantly associated with NICU admission, with Q1 having the highest risk. The receiver operating characteristic (ROC) curve suggested combining Q1 and Q2 for the best prediction of NICU admission, indicating that shorter mothers face a higher risk of neonates requiring NICU care.

CONCLUSION

Maternal short stature could be a valuable predictor of LBW and NICU admission risk. It may be a screening tool to assess these risks in healthcare settings. However, further research is needed to explore this association's underlying mechanisms and potential interventions.

Meta-analysis of genome-wide association studies of gestational duration and spontaneous preterm birth identifies new maternal risk loci

BACKGROUND

Preterm birth (<37 weeks of gestation) is a major cause of neonatal death and morbidity. Up to 40% of the variation in timing of birth results from genetic factors, mostly due to the maternal genome.

METHODS

We conducted a genome-wide meta-analysis of gestational duration and spontaneous preterm birth in 68,732 and 98,370 European mothers, respectively.

RESULTS

The meta-analysis detected 15 loci associated with gestational duration, and four loci associated with preterm birth. Seven of the associated loci were novel. The loci mapped to several biologically plausible genes, for example HAND2 whose expression was previously shown to decrease during gestation, associated with gestational duration, and GC (Vitamin D-binding protein), associated with preterm birth. Downstream in silico-analysis suggested regulatory roles as underlying mechanisms for the associated loci. LD score regression found birth weight measures as the most strongly correlated traits, highlighting the unique nature of spontaneous preterm birth phenotype. Tissue expression and colocalization analysis revealed reproductive tissues and immune cell types as the most relevant sites of action.

CONCLUSION

We report novel genetic risk loci that associate with preterm birth or gestational duration, and reproduce findings from previous genome-wide association studies. Altogether, our findings provide new insight into the genetic background of preterm birth. Better characterization of the causal genetic mechanisms will be important to public health as it could suggest new strategies to treat and prevent preterm birth.

Predictive factors of catch-up growth in term, small for gestational age infants: a two-year prospective observational study in Algeria

OBJECTIVES

Most small for gestational age (SGA) infants show catch-up growth but the minority who do not may benefit from growth-promoting treatment. We determined the prevalence of, and risk factors for, failure to show catch-up growth in term SGA infants.

METHODS

Prospective observational study of infants born at 37-42 weeks gestation between December 2012 and March 2014 with birth weight <10th percentile. Length, weight and head circumference were measured from birth to 2 years.

RESULTS

Of 457 (3.9 %) term infants with SGA, 446 (97.6 %) were followed up until 2 years. At 24 months, supine length, weight and head circumference were ≥-2 standard deviation score (SDS) in 87.9 , 96.4 and 97.1 % subjects, with persistent short stature in 12.1 %. In a multivariate analysis, the independent predictors of failure to show catch-up growth at 24 months were: maternal height <150 cm, difference between mid-parental height and birth length of ≥2.2 SDS, height at 24 months <-2 SDS below mid-parental height SDS, history of SGA, ponderal index <3rd centile and duration of breast feeding <3 months.

CONCLUSIONS

This study provides data concerning the epidemiology of SGA in Algeria and the factors associated with post-natal growth. Establishing which children remain short at 2 years has identified a cohort of patients requiring continuing follow up, with a view to instituting growth hormone therapy in selected cases. These results favour the setting up of an integrated national program to register SGA infants at birth, with re-evaluation at 2 years. (250 words).

Influence of parental anthropometry and gestational weight gain on intrauterine growth and neonatal outcomes: Findings from the MAI cohort study in rural India

Poor foetal growth and subsequent low birth weight are associated with an increased risk for disease later in life. Identifying parental factors that determine foetal growth are important to curbing intergenerational malnutrition, especially among disadvantaged populations in the global south where undernutrition rates are high. The objective of this study was to assess the relationships between parental biometry, intrauterine growth and neonatal outcomes, while factoring in socioeconomic status of historically disadvantaged households in rural India. Using data from the prospective longitudinal cohort, pregnant women from rural Pune, India (n = 134) were assessed between August 2020 and November 2022. Data on socio-demography, ultrasound measurements, parental and foetal anthropometry were collected. Multiple linear regression models were run to predict determinants of foetal intrauterine and neonatal growth (p value<0.05). The dependent variables were ultrasound measurements and neonatal biometry, and independent variables were gestational weight gain, parental and mid-parental height. Mean(±SD) maternal age, maternal height, paternal height and mid-parental height were 22.8±3.7 years, 153.6±5.5cm, 165.9±6.5cm and 159.1±8.7cm, respectively. Pre-pregnancy body mass index and gestational weight gain was 20.5±4.0 kg/m2 and 9.8±3.7kg respectively. Mid-parental height and gestational weight gain were strongly correlated with neonatal growth and foetal intrauterine growth (p<0.05); however, the correlation peaked at 28 weeks of gestation (p<0.05). Gestational weight gain (B = 28.7, p = 0.001) and mid-parental height (B = 14.3, p = 0.001) were identified as strong determinants of foetal-intrauterine growth and neonatal anthropometry at birth. Maternal height was found to influence length of male neonate (B = 0.18, p = 0.001), whereas, paternal height influenced length of the female neonate (B = 0.11, p = 0.01). Parental socio-economic status, biometry and maternal gestational weight gain influence growth of the child starting from the intrauterine period. Our study underlines the need for interventions during pre-pregnancy, as well as during pregnancy, for optimal weight gain and improved foetal and neonatal outcomes.

Health of neonates born in the maternity hospital in Bern, Switzerland, 1880-1900 and 1914-1922

The identification of factors impeding normal fetal development and growth is crucial for improving neonatal health. Historical studies are relevant because they show which parameters have influenced neonatal health in the past in order to better understand the present. We studied temporal changes of neonatal health outcomes (birth weight, gestational age, stillbirth rate) and the influence of different cofactors in two time periods. Moreover, we investigated particularly neonatal health in the wake of the 1918/19 influenza pandemic. Data were transcribed from the Bern Maternity Hospital and consists of two time periods: A) The years 1880, 1885, 1890, 1895 and 1900 (N = 1530, births' coverage 20%); B) The years 1914-1922 (N = 6924, births' coverage 40-50%). Linear regression models were used to estimate the effect of birth year on birth weight, and logistic regression models to estimate the effect of birth year and of the exposure to the pandemic on premature birth, stillborn and low birth weight (LBW). Mean birth weight increased only minimally between the two datasets; whereas, in the years 1914-1922, the preterm birth and stillbirth rates were markedly reduced compared with the years 1880-1900. Sex, parity, gestational age and maternal age were significantly associated with birth weight in both time periods. The probability of LBW was significantly increased in 1918 (OR 1.49 (95% CI 1.00-2.23)) and in 1919 (OR 1.55 (95% CI 1.02-2.36)) compared to 1914. Mothers who were heavily exposed to the influenza pandemic during pregnancy had a higher risk of stillbirth (OR 2.27 (95% CI 1.32-3.9)). This study demonstrated that factors influencing neonatal health are multifactorial but similar in both time periods. Moreover, the exposure to the 1918/19 pandemic was less associated with LBW and more associated with an increased risk of stillbirth. If this trend is confirmed by further studies, it could indicate some consistency across pandemics, as similar patterns have recently been shown for COVID-19.

Intergenerational transmission of height in a historical population: From taller mothers to larger offspring at birth (and as adults)

Changes in growth and height reflect changes in nutritional status and health. The systematic surveillance of growth can suggest areas for interventions. Moreover, phenotypic variation has a strong intergenerational component. There is a lack of historical family data that can be used to track the transmission of height over subsequent generations. Maternal height is a proxy for conditions experienced by one generation that relates to the health/growth of future generations. Cross-sectional/cohort studies have shown that shorter maternal height is closely associated with lower birth weight of offspring. We analyzed the maternal height and offspring weight at birth in the maternity hospital in Basel, Switzerland, from 1896 to 1939 (N = ∼12,000) using generalized additive models (GAMs). We observed that average height of the mothers increased by ∼4 cm across 60 birth years and that average birth weight of their children shows a similarly shaped and upward trend 28 years later. Our final model (adjusted for year, parity, sex of the child, gestational age, and maternal birth year) revealed a significant and almost linear association between maternal height and birth weight. Maternal height was the second most important variable modeling birth weight, after gestational age. In addition, we found a significant association between maternal height and aggregated average height of males from the same birth years at time of conscription, 19 years later. Our results have implications for public health: When (female/maternal) height increases due to improved nutritional status, size at birth-and subsequently also the height in adulthood of the next generation-increases as well. However, the directions of development in this regard may currently differ depending on the world region.

Annual Research Review: Towards a deeper understanding of nature and nurture: combining family-based quasi-experimental methods with genomic data

Distinguishing between the effects of nature and nurture constitutes a major research goal for those interested in understanding human development. It is known, for example, that many parent traits predict mental health outcomes in children, but the causal processes underlying such associations are often unclear. Family-based quasi-experimental designs such as sibling comparison, adoption and extended family studies have been used for decades to distinguish the genetic transmission of risk from the environmental effects family members potentially have on one another. Recently, these designs have been combined with genomic data, and this combination is fuelling a range of exciting methodological advances. In this review we explore these advances - highlighting the ways in which they have been applied to date and considering what they are likely to teach us in the coming years about the aetiology and intergenerational transmission of psychopathology.

Environmental enteric dysfunction: gut and microbiota adaptation in pregnancy and infancy

Environmental enteric dysfunction (EED) is a subclinical syndrome of intestinal inflammation, malabsorption and barrier disruption that is highly prevalent in low- and middle-income countries in which poverty, food insecurity and frequent exposure to enteric pathogens impair growth, immunity and neurodevelopment in children. In this Review, we discuss advances in our understanding of EED, intestinal adaptation and the gut microbiome over the 'first 1,000 days' of life, spanning pregnancy and early childhood. Data on maternal EED are emerging, and they mirror earlier findings of increased risks for preterm birth and fetal growth restriction in mothers with either active inflammatory bowel disease or coeliac disease. The intense metabolic demands of pregnancy and lactation drive gut adaptation, including dramatic changes in the composition, function and mother-to-child transmission of the gut microbiota. We urgently need to elucidate the mechanisms by which EED undermines these critical processes so that we can improve global strategies to prevent and reverse intergenerational cycles of undernutrition.

Does maternal stature modify the association between infants who are small or large for gestational age and adverse perinatal outcomes? A retrospective cohort study

OBJECTIVE

To investigate the effect of maternal stature on adverse birth outcomes and quantify perinatal risks associated with small- and large-for-gestational age infants (SGA and LGA, respectively) born to mothers of short, average, and tall stature.

DESIGN

Retrospective cohort study.

SETTING

USA, 2016-2017.

POPULATION

Women with a singleton live birth (N = 7 325 741).

METHODS

Using data from the National Center for Health Statistics, short and tall stature were defined as <10th and >90th centile of the maternal height distribution. Modified Poisson regression was used to estimate adjusted risk ratios (aRRs) and 95% confidence intervals (95% CIs).

MAIN OUTCOME MEASURES

Preterm birth (<37 weeks of gestation), neonatal intensive care unit (NICU) admission and severe neonatal morbidity/mortality (SNMM).

RESULTS

With increased maternal height, the risk of adverse outcomes increased in SGA infants and decreased in LGA infants compared with infants appropriate-for-gestational age (AGA) (p < 0.001). Infants who were SGA born to women of tall stature had the highest risk of NICU admission (aRR 1.98, 95% CI 1.91-2.05; p < 0.001), whereas LGA infants born to women of tall stature had the lowest risk (aRR 0.85, 95% CI 0.82-0.88; p < 0.001), compared with AGA infants born to women of average stature. LGA infants born to women of short stature had an increased risk of NICU admission and SNMM, compared with AGA infants born to women of average stature (aRR 1.32, 95% CI 1.27-1.38; aRR 1.21, 95% CI 1.13-1.29, respectively).

CONCLUSIONS

Maternal height modifies the association between SGA and LGA status at birth and neonatal outcomes. This quantification of risk can assist healthcare providers in monitoring fetal growth, and optimising neonatal care and follow-up.

Birth anthropometry among three Asian racial groups in Singapore: proposed new growth charts

OBJECTIVE

We analysed birth anthropometry of babies of Chinese, Malay and Indian ancestry living in Singapore with an aim to develop gestational age (GA) and gender-specific birth anthropometry charts and compare these with the widely used Fenton charts.

DESIGN

Retrospective observational study.

SETTING

Department of Neonatology, National University Hospital, Singapore.

POPULATION

We report data from 52 220 infants, born between 1991-1997 and 2010-2017 in Singapore.

METHODS

Anthropometry charts were built using smoothened centile curves and compared with Fenton's using binomial test. Birth weight (BW), crown-heel length and head circumference (HC) were each modelled with maternal exposures using general additive model.

MAIN OUTCOME MEASURES

BW, crown-heel length and HC.

RESULTS

There were 22 248 Chinese (43%), 16 006 Malay (31%) and 8543 Indian (16%) babies. Mean BW was 3103 g (95% CI 3096 to 3109), 3075 g (95% CI 3067 to 3083) and 3052 g (95% CI 3041 to 3062) for Chinese, Malays and Indians, respectively. When exposed to a uniform socioeconomic environment, intrauterine growth and birth anthropometry of studied races were almost identical. From our GA-specific anthropometric charts until about late prematurity, Asian growth curves mirrored that of Fenton's; thereafter, Asian babies showed a reduction in growth velocity.

CONCLUSIONS

These findings suggest that Asian babies living in relatively uniform socioeconomic strata exhibit similar growth patterns. There is a slowing of growth among Asian babies towards term, prompting review of existing birth anthropometry charts. The proposed charts will increase accuracy of identification of true fetal growth restriction as well as true postnatal growth failure in preterm infants when applied to the appropriate population.

The estimation of environmental and genetic parental influences

Parents share half of their genes with their children, but they also share background social factors and actively help shape their child's environment - making it difficult to disentangle genetic and environmental causes of parent-offspring similarity. While adoption and extended twin family designs have been extremely useful for distinguishing genetic and nongenetic parental influences, these designs entail stringent assumptions about phenotypic similarity between relatives and require samples that are difficult to collect and therefore are typically small and not publicly shared. Here, we describe these traditional designs, as well as modern approaches that use large, publicly available genome-wide data sets to estimate parental effects. We focus in particular on an approach we recently developed, structural equation modeling (SEM)-polygenic score (PGS), that instantiates the logic of modern PGS-based methods within the flexible SEM framework used in traditional designs. Genetically informative designs such as SEM-PGS rely on different and, in some cases, less rigid assumptions than traditional approaches; thus, they allow researchers to capitalize on new data sources and answer questions that could not previously be investigated. We believe that SEM-PGS and similar approaches can lead to improved insight into how nature and nurture combine to create the incredible diversity underlying human behavior.

The causal association between maternal smoking around birth on childhood asthma: A Mendelian randomization study

To explore the causal relationship between maternal smoking around birth and childhood asthma using Mendelian randomization (MR). Using the data from large-scale genome-wide association studies, we selected independent genetic loci closely related to maternal smoking around birth and maternal diseases as instrumental variables and used MR methods. In this study, we considered the inverse variance weighted method (MR-IVW), weighted median method, and MR-Egger regression. We investigated the causal relationship between maternal smoking around birth and maternal diseases in childhood asthma using the odds ratio (OR) as an evaluation index. Multivariable MR (MVMR) included maternal history of Alzheimer's disease, illnesses of the mother: high blood pressure and illnesses of the mother: heart diseaseas covariates to address potential confounding. Sensitivity analyses were evaluated for weak instrument bias and pleiotropic effects. It was shown with the MR-IVW results that maternal smoking around birth increased the risk of childhood asthma by 1.5% (OR = 1.0150, 95% CI: 1.0018-1.0283). After the multivariable MR method was used to correct for relevant covariates, the association effect between maternal smoking around birth and childhood asthma was still statistically significant (P < 0.05). Maternal smoking around birth increases the risk of childhood asthma.

Genetics, epigenetics, and transcriptomics of preterm birth

Preterm birth contributes significantly to neonatal mortality and morbidity. Despite its global significance, there has only been limited progress in preventing preterm birth. Spontaneous preterm birth (sPTB) results from a wide variety of pathological processes. Although many non-genetic risk factors influence the timing of gestation and labor, compelling evidence supports the role of substantial genetic and epigenetic influences and their interactions with the environment contributing to sPTB. To investigate a common and complex disease such as sPTB, various approaches such as genome-wide association studies, whole-exome sequencing, transcriptomics, and integrative approaches combining these with other 'omics studies have been used. However, many of these studies were typically small or focused on a single ethnicity or geographic region with limited data, particularly in populations at high risk for sPTB, or lacked a robust replication. These studies found many genes involved in the inflammation and immunity-related pathways that may affect sPTB. Recent studies also suggest the role of epigenetic modifications of gene expression by the environmental signals as a potential contributor to the risk of sPTB. Future genetic studies of sPTB should continue to consider the contributions of both maternal and fetal genomes as well as their interaction with the environment.

Research Review: How to interpret associations between polygenic scores, environmental risks, and phenotypes

BACKGROUND

Genetic influences are ubiquitous as virtually all phenotypes and most exposures typically classified as environmental have been found to be heritable. A polygenic score summarises the associations between millions of genetic variants and an outcome in a single value for each individual. Ever lowering costs have enabled the genotyping of many samples relevant to child psychology and psychiatry research, including cohort studies, leading to the proliferation of polygenic score studies. It is tempting to assume that associations detected between polygenic scores and phenotypes in those studies only reflect genetic effects. However, such associations can reflect many pathways (e.g. via environmental mediation) and biases.

METHODS

Here, we provide a comprehensive overview of the many reasons why associations between polygenic scores, environmental exposures, and phenotypes exist. We include formal representations of common analyses in polygenic score studies using structural equation modelling. We derive biases, provide illustrative empirical examples and, when possible, mention steps that can be taken to alleviate those biases.

RESULTS

Structural equation models and derivations show the many complexities arising from jointly modelling polygenic scores with environmental exposures and phenotypes. Counter-intuitive examples include that: (a) associations between polygenic scores and phenotypes may exist even in the absence of direct genetic effects; (b) associations between child polygenic scores and environmental exposures can exist in the absence of evocative/active gene-environment correlations; and (c) adjusting an exposure-outcome association for a polygenic score can increase rather than decrease bias.

CONCLUSIONS

Strikingly, using polygenic scores may, in some cases, lead to more bias than not using them. Appropriately conducting and interpreting polygenic score studies thus requires researchers in child psychology and psychiatry and beyond to be versed in both epidemiological and genetic methods or build on interdisciplinary collaborations.

Birth weight distribution in Golden and Labrador retriever dogs: A similar morphotype with a different trend. Preliminary data

Birth weight (bW) is considered an indicator of neonatal maturity and a predictor of neonatal mortality. According to its importance, many efforts have been made so far to identify physiological body weight ranges at birth. Due to the high heterogeneity among breeds, optimal bW is difficult to define in dogs. The aim of this study was to carefully analyze the shape and pattern of the bW distribution in dogs. Furthermore, the role of breed on bW determination was specifically investigated in relation to maternal (age, weight, height, diet, season, litter size) and neonatal (sex, malformations, assistance at birth) aspects. For these purposes two canine breeds with very similar phenotypic characteristics, Golden and Labrador retrievers, were selected. An accurate statistical model to explore bW distribution and compare it between Goldens and Labradors was developed. At birth most of the Golden and Labrador pups (estimated 95th percentile) weighed up to 630 g and 500 g, respectively. The estimated 5th percentile of bW distributions was 295 g in Golden and 290 g in Labrador pups. These lowest values could be indicative cut-offs of underweight pups. The probability of neonatal mortality within 1 week of life decreased with increasing bW (P = 0.031) and was higher in Golden than Labrador pups even though this difference was not significant. In conclusion, our results suggest that genetics have a relevant influence on the determination of birth weight which is confirmed to be closely associated with neonatal mortality.

Assessing whether genetic scores explain extra variation in birthweight, when added to clinical and anthropometric measures

BACKGROUND

Human birthweight is a complex, multifactorial trait. Maternal characteristics contribute to birthweight variation by influencing the intrauterine environment. Variation explained by genetic effects is also important, but their contributions have not been assessed alongside other key determinants. We aimed to investigate variance in birthweight explained by genetic scores in addition to easily-measurable clinical and anthropometric variables.

METHODS

We analysed 549 European-ancestry parent-offspring trios from a UK community-based birth cohort. We investigated variance explained in birthweight (adjusted for sex and gestational age) in multivariable linear regression models including genetic scores, routinely-measured maternal characteristics, and parental anthropometric variables. We used R-Squared (R²) to estimate variance explained, adjusted R-squared (Adj-R²) to assess improvement in model fit from added predictors, and F-tests to compare nested models.

RESULTS

Maternal and fetal genetic scores together explained 6.0% variance in birthweight. A model containing maternal age, weight, smoking, parity and 28-week fasting glucose explained 21.7% variance. Maternal genetic score explained additional variance when added to maternal characteristics (Adj-R² = 0.233 vs Adj-R² = 0.210, p < 0.001). Fetal genetic score improved variance explained (Adj-R² = 0.264 vs 0.248, p < 0.001) when added to maternal characteristics and parental heights.

CONCLUSIONS

Genetic scores account for variance explained in birthweight in addition to easily measurable clinical variables. Parental heights partially capture fetal genotype and its contribution to birthweight, but genetic scores explain additional variance. While the genetic contribution is modest, it is comparable to that of individual clinical characteristics such as parity, which suggests that genetics could be included in tools aiming to predict risk of high or low birthweights.

Estimating effects of parents' cognitive and non-cognitive skills on offspring education using polygenic scores

Understanding how parents' cognitive and non-cognitive skills influence offspring education is essential for educational, family and economic policy. We use genetics (GWAS-by-subtraction) to assess a latent, broad non-cognitive skills dimension. To index parental effects controlling for genetic transmission, we estimate indirect parental genetic effects of polygenic scores on childhood and adulthood educational outcomes, using siblings (N = 47,459), adoptees (N = 6407), and parent-offspring trios (N = 2534) in three UK and Dutch cohorts. We find that parental cognitive and non-cognitive skills affect offspring education through their environment: on average across cohorts and designs, indirect genetic effects explain 36-40% of population polygenic score associations. However, indirect genetic effects are lower for achievement in the Dutch cohort, and for the adoption design. We identify potential causes of higher sibling- and trio-based estimates: prenatal indirect genetic effects, population stratification, and assortative mating. Our phenotype-agnostic, genetically sensitive approach has established overall environmental effects of parents' skills, facilitating future mechanistic work.

Using adopted individuals to partition indirect maternal genetic effects into prenatal and postnatal effects on offspring phenotypes

Maternal genetic effects can be defined as the effect of a mother's genotype on the phenotype of her offspring, independent of the offspring's genotype. Maternal genetic effects can act via the intrauterine environment during pregnancy and/or via the postnatal environment. In this manuscript, we present a simple extension to the basic adoption design that uses structural equation modelling (SEM) to partition maternal genetic effects into prenatal and postnatal effects. We examine the power, utility and type I error rate of our model using simulations and asymptotic power calculations. We apply our model to polygenic scores of educational attainment and birth weight associated variants, in up to 5,178 adopted singletons, 943 trios, 2687 mother-offspring pairs, 712 father-offspring pairs and 347,980 singletons from the UK Biobank. Our results show the expected pattern of maternal genetic effects on offspring birth weight, but unexpectedly large prenatal maternal genetic effects on offspring educational attainment. Sensitivity and simulation analyses suggest this result may be at least partially due to adopted individuals in the UK Biobank being raised by their biological relatives. We show that accurate modelling of these sorts of cryptic relationships is sufficient to bring type I error rate under control and produce asymptotically unbiased estimates of prenatal and postnatal maternal genetic effects. We conclude that there would be considerable value in following up adopted individuals in the UK Biobank to determine whether they were raised by their biological relatives, and if so, to precisely ascertain the nature of these relationships. These adopted individuals could then be incorporated into informative statistical genetics models like the one described in our manuscript to further elucidate the genetic architecture of complex traits and diseases.

Exploring and mitigating potential bias when genetic instrumental variables are associated with multiple non-exposure traits in Mendelian randomization

With the increasing size and number of genome-wide association studies, individual single nucleotide polymorphisms are increasingly found to associate with multiple traits. Many different mechanisms could result in proposed genetic IVs for an exposure of interest being associated with multiple non-exposure traits, some of which could bias MR results. We describe and illustrate, through causal diagrams, a range of scenarios that could result in proposed IVs being related to non-exposure traits in MR studies. These associations could occur due to five scenarios: (i) confounding, (ii) vertical pleiotropy, (iii) horizontal pleiotropy, (iv) reverse causation and (v) selection bias. For each of these scenarios we outline steps that could be taken to explore the underlying mechanism and mitigate any resulting bias in the MR estimation. We recommend MR studies explore possible IV-non-exposure associations across a wider range of traits than is usually the case. We highlight the pros and cons of relying on sensitivity analyses without considering particular pleiotropic paths versus systematically exploring and controlling for potential pleiotropic or other biasing paths via known traits. We apply our recommendations to an illustrative example of the effect of maternal insomnia on offspring birthweight in UK Biobank.

Is birthweight influenced equally by maternal and paternal anthropometry?

OBJECTIVES

To elucidate the influence of parental biometric factors on fetal birthweight (BW).

STUDY DESIGN

This prospective study was conducted between 2015 and 2017 in Hadassah University Hospital. Inclusion criteria included singletons that were born to healthy mothers at 37-41 weeks' gestation and had no growth abnormality or congenital malformation. Maternal and paternal head circumference, weight, and height were measured. Other data including neonatal head circumference and neonatal birthweight were also collected. Neonatal head circumference and birthweight percentiles were converted to sex-specific ranks according to the neonatal Intergrowth 21 charts (rank = 1 for percentile <3, rank = 2 for percentile 3-10, etc.).

RESULTS

One hundred and ninety-nine trios (mother, father, and neonate) were included in the final analysis. In univariate analysis, maternal head circumference (p = .006), maternal height (p = .001), maternal weight before pregnancy (p < .001), maternal weight at term (p < .001), gestational weight gain (p = .009), paternal height (p = .018), neonatal head circumference (p < .001), and neonatal head circumference percentile rank (p < .001) were significant predictors of neonatal birthweight percentile rank. In multivariate regression, the three factors that were significant independent predictors of neonatal birthweight percentile rank were maternal weight before pregnancy (p = .047), maternal weight at term (p = .01), and neonatal head circumference percentile rank (p < .001). No interaction was found between neonatal sex and any of the tested variables. Neonatal sex-specific multivariate analysis showed that maternal height (p = .013), gestational weight gain (p = .005), and neonatal head circumference percentile rank (p < .001) were predictors of birthweight percentile rank in males. Maternal weight at term (p < .001) and neonatal head circumference percentile rank (p < .001) were predictors of birthweight percentile rank in females.

CONCLUSIONS

Maternal height and weight parameters as well as neonatal head circumference percentile rank were found to be independent predictors of birthweight percentile rank. Paternal parameters did not show any significant association in multivariable analysis. The biological regulation of fetal size is assumed to be the result of strong evolutionary selection. As the fetus must pass through the mother's birth canal, there should be a natural match between maternal and fetal size to ensure the successful birth and survival of mother and offspring.

Smoking during pregnancy is associated with child overweight independent of maternal pre-pregnancy BMI and genetic predisposition to adiposity

High maternal body mass index (BMI) and smoking during pregnancy are risk factors for child overweight. Maternal smoking tends to reduce her BMI and the association of smoking with child overweight may be confounded by or interacting with maternal genetic predisposition to adiposity. In the Danish National Birth Cohort, we investigated whether smoking during pregnancy is associated with child BMI/overweight independent of pre-pregnancy BMI and maternal genetic predisposition to adiposity estimated as total, transmitted and non-transmitted genetic risk scores (GRSs) based on 941 common genetic variants associated with BMI. Smoking during pregnancy was associated with higher child BMI and higher odds of child overweight in a dose–response relationship. The odds ratio (95% CI) for smoking 11 + cigarettes in third trimester versus no smoking was 2.42 (1.30; 4.50), irrespective of maternal BMI and maternal GRSs (total, transmitted or non-transmitted). There were no statistically significant interactions between maternal GRSs and smoking (all p-values for interactions > 0.05). In conclusion, in this study, smoking during pregnancy exhibits a dose–response association with increased child BMI/overweight, independent of maternal pre-pregnancy BMI, maternal transmitted, and non-transmitted genetic predisposition to adiposity. Avoidance of smoking during pregnancy may help prevent childhood obesity irrespective of the mother–child genetic predisposition.

Population-based rates, risk factors and consequences of preterm births in South-Asia and sub-Saharan Africa: A multi-country prospective cohort study

BACKGROUND

Preterm birth is the leading cause of neonatal deaths in low middle-income countries (LMICs), yet there exists a paucity of high-quality data from these countries. Most modelling estimates are based on studies using inaccurate methods of gestational age assessment. We aimed to fill this gap by measuring the population-based burden of preterm birth using early ultrasound dating in five countries in South-Asian and sub-Saharan Africa.

METHODS

We identified women early in pregnancy (<20 weeks based on last menstrual period) by home visits every 2-3 months (except in Zambia where they were identified at antenatal care clinics) in 5 research sites in South-Asia and sub-Saharan Africa between July 2012 and September 2016. Trained sonographers performed an ultrasound scan for gestational age dating. Women were enrolled if they were 8-19 weeks pregnant on ultrasound. Women <8 weeks were rescheduled for repeat scans after 4 weeks, and identified women were followed through pregnancy until 6 weeks postpartum. Site-specific rates and proportions were calculated and a logistic regression model was used to predict the risk factors of preterm birth.

RESULTS

Preterm birth rates ranged from 3.2% in Ghana to 15.7% in Pakistan. About 46% of all neonatal deaths occurred among preterm infants, 49% in South Asia and 40% in sub-Saharan Africa. Fourteen percent of all preterm infants died during the neonatal period. The mortality was 37.6% for early preterm babies (<34 weeks), 5.9% for late preterm babies (34 to <37 weeks), and 1.7% for term babies (37 to <42 weeks). Factors associated lower gestation at birth included South-Asian region (adjusted mean difference (Adj MD) = -6.2 days, 95% confidence interval (CI) = -5.5, -6.9), maternal morbidities (Adj MD = -3.4 days, 95% CI = -4.6, -2.2), multiple pregnancies (Adj MD = -17.8 days, 95% CI = -19.9,-15.8), adolescent pregnancy (Adj MD = -2.7 days, 95% CI = -3.7, -1.6) and lowest wealth quintile (Adj MD = -1.3 days, 95% CI = -2.4, -0.3).

CONCLUSIONS

Preterm birth rates are higher in South Asia than in sub-Saharan Africa and contribute to 49% and 40% of all neonatal deaths in the two regions, respectively. Adolescent pregnancy and maternal morbidities are modifiable risk factors associated with preterm birth.

Exploring the causal effect of maternal pregnancy adiposity on offspring adiposity: Mendelian randomisation using polygenic risk scores

BACKGROUND

Greater maternal adiposity before or during pregnancy is associated with greater offspring adiposity throughout childhood, but the extent to which this is due to causal intrauterine or periconceptional mechanisms remains unclear. Here, we use Mendelian randomisation (MR) with polygenic risk scores (PRS) to investigate whether associations between maternal pre-/early pregnancy body mass index (BMI) and offspring adiposity from birth to adolescence are causal.

METHODS

We undertook confounder adjusted multivariable (MV) regression and MR using mother-offspring pairs from two UK cohorts: Avon Longitudinal Study of Parents and Children (ALSPAC) and Born in Bradford (BiB). In ALSPAC and BiB, the outcomes were birthweight (BW; N = 9339) and BMI at age 1 and 4 years (N = 8659 to 7575). In ALSPAC only we investigated BMI at 10 and 15 years (N = 4476 to 4112) and dual-energy X-ray absorptiometry (DXA) determined fat mass index (FMI) from age 10-18 years (N = 2659 to 3855). We compared MR results from several PRS, calculated from maternal non-transmitted alleles at between 29 and 80,939 single nucleotide polymorphisms (SNPs).

RESULTS

MV and MR consistently showed a positive association between maternal BMI and BW, supporting a moderate causal effect. For adiposity at most older ages, although MV estimates indicated a strong positive association, MR estimates did not support a causal effect. For the PRS with few SNPs, MR estimates were statistically consistent with the null, but had wide confidence intervals so were often also statistically consistent with the MV estimates. In contrast, the largest PRS yielded MR estimates with narrower confidence intervals, providing strong evidence that the true causal effect on adolescent adiposity is smaller than the MV estimates (Pdifference = 0.001 for 15-year BMI). This suggests that the MV estimates are affected by residual confounding, therefore do not provide an accurate indication of the causal effect size.

CONCLUSIONS

Our results suggest that higher maternal pre-/early-pregnancy BMI is not a key driver of higher adiposity in the next generation. Thus, they support interventions that target the whole population for reducing overweight and obesity, rather than a specific focus on women of reproductive age.

Maternal respiratory health and intrauterine exposure-driven birthweight: a two-sample Mendelian randomization study

BACKGROUND

Observationally, poorer maternal respiratory health is associated with poorer birth outcomes, possibly confounded by socioeconomic position and other maternal attributes. We used multivariable Mendelian randomization (MR) to obtain unconfounded estimates of effect of maternal lung function on birthweight, independent of maternal height.

METHODS

Single nucleotide polymorphisms (SNPs) for forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC) in women were obtained from publicly available summary statistics from the UK Biobank. SNPs for asthma were obtained from the Trans-National Asthma Genetic consortium. SNPs for height in women were obtained from the Genetic Investigation of Anthropometric Traits consortium and the genetic estimates were obtained the UK Biobank. The genetic associations with maternally-driven birthweight were obtained from the Early Growth Genetics consortium. Multivariable MR estimates were obtained using inverse variance weighting with multivariable MR-Egger as sensitivity analysis.

RESULTS

Maternal lung capacity, as indicated by FVC, was positively associated with maternally-driven birthweight (0.08 per standard deviation, 95% confidence interval 0.01 to 0.15) independent of maternal height, whereas no clear such associations were shown for maternal airway function, indicated by FEV1 and peak expiratory flow, or for asthma, on maternally-driven birthweight. Similar findings were shown using MR-Egger.

CONCLUSIONS

These findings suggest that maternal lung function, especially lung capacity independent of maternal height, is directly associated with maternally-driven birthweight, and highlights the importance of maternal respiratory health in fetal growth.

Placenta mediates the effect of maternal hypertension polygenic score on offspring birth weight: a study of birth cohort with fetal growth velocity data

BACKGROUND

Low birth weight (LBW) and fetal growth restriction are associated with the development of cardio-metabolic diseases later in life. A recent Mendelian randomization study concluded that the susceptibility of LBW infants to develop hypertension during adulthood is due to the inheritance of hypertension genes from the mother and not to an unfavorable intrauterine environment. Therein, a negative linear association has been assumed between genetically estimated maternal blood pressure (BP) and birth weight, while the observed relationship between maternal BP and birth weight is substantially different from that assumption. As many hypertension genes are likely involved in vasculature development and function, we hypothesized that BP-increasing genetic variants could affect birth weight by reducing the growth of the placenta, a highly vascular organ, without overtly elevating the maternal BP.

METHODS

Using a birth cohort in the Japanese population possessing time-series fetal growth velocity data as a target and a GWAS summary statistics of BioBank Japan as a base data, we performed polygenic score (PGS) analyses for systolic BP (SBP), diastolic BP, mean arterial pressure, and pulse pressure. A causal mediation analysis was performed to assess the meditation effect of placental weight on birth weight reduced by maternal BP-increasing PGS. Maternal genetic risk score constituted of only "vasculature-related" BP single nucleotide polymorphisms (SNPs) was constructed to examine the involvement of vascular genes in the mediation effect of placental weight. We identified gestational week in which maternal SBP-increasing PGS significantly decreased fetal growth velocity.

RESULTS

We observed that maternal SBP-increasing PGS was negatively associated with offspring birth weight. A causal mediation analysis revealed that a large proportion of the total maternal PGS effect on birth weight was mediated by placental weight. The placental mediation effect was remarkable when genetic risk score was constituted of "vasculature-related" BP SNPs. The inverse association between maternal SBP PGS and fetal growth velocity only became apparent in late gestation.

CONCLUSIONS

Our study suggests that maternal hypertension genes are strongly associated with placental growth and that fetal growth inhibition is induced through the intrauterine environment established by the placenta.

Identification of maternal continuous glucose monitoring metrics related to newborn birth weight in pregnant women with gestational diabetes

PURPOSE

To identify the specific glucose metrics derived from maternal continuous glucose monitoring (CGM) data, which were associated with a higher percentile of offspring birth weight.

METHODS

In this cohort study, we recruited singleton pregnant women with GDM who underwent CGM for 5-14 days at a mean of 28.8 gestational weeks between Jan 2017 and Nov 2018. Commonly used single summary glucose metrics of glucose exposure (including mean 24-h, daytime, and nighttime glucose level) and variability (including J-index and mean amplitude of glycaemic excursions) were derived from CGM data. A novel comprehensive glucose metric-hours per-day spent in a severe variability glucose mode (HSSV)-was identified using the spectral clustering method, which reflects both glucose level and variability. Multiple linear regression models were used to estimate the associations of sex- and gestational age-adjusted birth weight percentile with CGM parameters.

RESULTS

Ninety-seven women comprising 127,279 glucose measurements were included. Each 1-SD increase in maternal nighttime mean glucose level and HSSV was associated with 6.0 (95% CI 0.4, 11.5) and 6.3 (95% CI 0.4, 12.2) percentage points increase in birth weight percentile, respectively. No associations were found between other glucose metrics and birth weight percentile.

CONCLUSION

Nighttime mean glucose level has a comparable effect size to HSSV in association with fetal growth, suggesting that endogenous hyperglycemia might drive the association between maternal hyperglycemia and birth weight. Further studies need to examine the effect of lowering nighttime glucose level and/or HSSV on preventing fetal overgrowth in GDM women.

Association of Parental Height With Offspring Stunting in 14 Low- and Middle-Income Countries

Background: Maternal height has been confirmed to be associated with offspring stunting in low- and middle-income countries (LMICs), but only limited studies have examined the paternal-offspring association, and few studies have examined the joint effect of maternal and paternal height on stunting.

Objective: To investigate the association between parental height and stunting of children aged under five in LMICs.

Methods: We obtained data from the Demographic and Health Surveys (DHS) conducted in 14 LMICs from 2006 to 2016. The association between maternal and paternal height and height-for-age z score (HAZ) of children aged under five was analyzed using a linear regression model in consideration of complex survey design, and regression coefficients (β) with 95% confidence intervals (CIs) were reported. Then, the association between maternal and paternal height quintile and child stunting was analyzed using a modified Poisson regression approach with robust error variance in consideration of complex survey design with adjustment for covariates. The effect estimates were expressed as relative risks (RRs) with 95% CIs.

Results: A total of 50,372 singleton children were included and the weighted prevalence of stunting was 34.5%. Both maternal height and paternal height were associated with child HAZ (β = 0.047; 95% CI, 0.043, 0.050; and β = 0.022; 95% CI, 0.018, 0.025, respectively). Compared with those born to the tallest mothers and fathers, children from the shortest mothers and the shortest fathers had higher risks of stunting (adjusted RR = 1.89; 95% CI, 1.78, 2.01; adjusted RR = 1.56; 95% CI, 1.47, 1.65, respectively). The mother-offspring associations are substantively larger than the father-offspring associations for each corresponding height quintile. Children from the shortest parents had the highest risk of stunting compared with children from the tallest parents (adjusted RR = 3.23; 95% CI, 2.83, 3.68).

Conclusions: Offspring born to short parents are at increased risk of stunting in LMICs, and this intergenerational effect is partly driven by maternal intrauterine influence. This suggests the importance of improving the nutritional status of children and adults in LMICs, especially female caregivers.

Integrative genetic, genomic and transcriptomic analysis of heat shock protein and nuclear hormone receptor gene associations with spontaneous preterm birth

Heat shock proteins are involved in the response to stress including activation of the immune response. Elevated circulating heat shock proteins are associated with spontaneous preterm birth (SPTB). Intracellular heat shock proteins act as multifunctional molecular chaperones that regulate activity of nuclear hormone receptors. Since SPTB has a significant genetic predisposition, our objective was to identify genetic and transcriptomic evidence of heat shock proteins and nuclear hormone receptors that may affect risk for SPTB. We investigated all 97 genes encoding members of the heat shock protein families and all 49 genes encoding nuclear hormone receptors for their potential role in SPTB susceptibility. We used multiple genetic and genomic datasets including genome-wide association studies (GWASs), whole-exome sequencing (WES), and placental transcriptomics to identify SPTB predisposing factors from the mother, infant, and placenta. There were multiple associations of heat shock protein and nuclear hormone receptor genes with SPTB. Several orthogonal datasets supported roles for SEC63, HSPA1L, SACS, RORA, and AR in susceptibility to SPTB. We propose that suppression of specific heat shock proteins promotes maintenance of pregnancy, whereas activation of specific heat shock protein mediated signaling may disturb maternal–fetal tolerance and promote labor.

The role of genetics in fetal programming of adult cardiometabolic disease

Disturbances affecting early development have broad repercussions on the individual's health during infancy and adulthood. Multiple observational studies throughout the years have shown that alterations of fetal growth are associated with increased cardiometabolic disease risks. However, the genetic component of this association only started to be investigated in the last 40 years, when single genes with distinct effects were investigated. Birth weight (BW), commonly reported as the outcome of developmental growth, has been estimated to be 20% to 60% heritable. Through Genome-Wide Association (GWA) meta-analyses, 190 different loci have been identified being associated with BW, and while many of these loci designate genes involved in glucose and lipid metabolism, with clear ties to fetal development, the role of others is not yet understood. In addition, due to its influence over the intrauterine environment, the maternal genotype also plays an important part in the determination of offspring BW, with the same loci having independent effects of different magnitude or even direction. There is still much to uncover regarding the genetic determinants of BW and the interactions between maternal, offspring, and even paternal genotype. To fully understand these, diverse and novel cohorts from multiple ancestries collecting extensive neonatal phenotype will be needed. This review compiles, chronologically, the main findings in the investigation of the genetics of BW.

Maternal factors associated with birth length in Gowa district, South Sulawesi province, Indonesia

OBJECTIVE

This study aims to determine the factors of the mother that influence the body length of the baby at birth.

METHODS

This study used a cross sectional design involving 269 babies born in several health centers in Gowa district. Measurement of body length is carried out a maximum of 72h after the baby is born, as well as the height and weight of the mother. Information regarding maternal age, parity, and gestational age were obtained by conducting interviews using a structured questionnaire. Data analysis used linear regression.

RESULTS

The results showed that maternal height (p=0.000) and gestational age (p=0.000) are correlated with the child's body length at birth. While maternal weight, parity and maternal age were not significantly associated (p>0.05).

CONCLUSION

In this study, it can be concluded that maternal factors that related to the child's body length are height and gestational age when the mother gives birth.

Bias and Precision of Parameter Estimates from Models Using Polygenic Scores to Estimate Environmental and Genetic Parental Influences

In a companion paper Balbona et al. (Behav Genet, in press), we introduced a series of causal models that use polygenic scores from transmitted and nontransmitted alleles, the offspring trait, and parental traits to estimate the variation due to the environmental influences the parental trait has on the offspring trait (vertical transmission) as well as additive genetic effects. These models also estimate and account for the gene-gene and gene-environment covariation that arises from assortative mating and vertical transmission respectively. In the current study, we simulated polygenic scores and phenotypes of parents and offspring under genetic and vertical transmission scenarios, assuming two types of assortative mating. We instantiated the models from our companion paper in the OpenMx software, and compared the true values of parameters to maximum likelihood estimates from models fitted on the simulated data to quantify the bias and precision of estimates. We show that parameter estimates from these models are unbiased when assumptions are met, but as expected, they are biased to the degree that assumptions are unmet. Standard errors of the estimated variances due to vertical transmission and to genetic effects decrease with increasing sample sizes and with increasing [Formula: see text] values of the polygenic score. Even when the polygenic score explains a modest amount of trait variation ([Formula: see text]), standard errors of these standardized estimates are reasonable ([Formula: see text]) for [Formula: see text] trios, and can even be reasonable for smaller sample sizes (e.g., down to 4K) when the polygenic score is more predictive. These causal models offer a novel approach for understanding how parents influence their offspring, but their use requires polygenic scores on relevant traits that are modestly predictive (e.g., [Formula: see text] as well as datasets with genomic and phenotypic information on parents and offspring. The utility of polygenic scores for elucidating parental influences should thus serve as additional motivation for large genomic biobanks to perform GWAS's on traits that may be relevant to parenting and to oversample close relatives, particularly parents and offspring.

Estimation of Parental Effects Using Polygenic Scores

Offspring resemble their parents for both genetic and environmental reasons. Understanding the relative magnitude of these alternatives has long been a core interest in behavioral genetics research, but traditional designs, which compare phenotypic covariances to make inferences about unmeasured genetic and environmental factors, have struggled to disentangle them. Recently, Kong et al. (2018) showed that by correlating offspring phenotypic values with the measured polygenic score of parents' nontransmitted alleles, one can estimate the effect of "genetic nurture"-a type of passive gene-environment covariation that arises when heritable parental traits directly influence offspring traits. Here, we instantiate this basic idea in a set of causal models that provide novel insights into the estimation of parental influences on offspring. Most importantly, we show how jointly modeling the parental polygenic scores and the offspring phenotypes can provide an unbiased estimate of the variation attributable to the environmental influence of parents on offspring, even when the polygenic score accounts for a small fraction of trait heritability. This model can be further extended to (a) account for the influence of different types of assortative mating, (b) estimate the total variation due to additive genetic effects and their covariance with the familial environment (i.e., the full genetic nurture effect), and (c) model situations where a parental trait influences a different offspring trait. By utilizing structural equation modeling techniques developed for extended twin family designs, our approach provides a general framework for modeling polygenic scores in family studies and allows for various model extensions that can be used to answer old questions about familial influences in new ways.

Mendelian randomisation approaches to the study of prenatal exposures: A systematic review

BACKGROUND

Mendelian randomisation (MR) designs apply instrumental variable techniques using genetic variants to study causal effects. MR is increasingly used to evaluate the role of maternal exposures during pregnancy on offspring health.

OBJECTIVES

We review the application of MR to prenatal exposures and describe reporting of methodologic challenges in this area.

DATA SOURCES

We searched PubMed, EMBASE, Medline Ovid, Cochrane Central, Web of Science, and Google Scholar.

STUDY SELECTION AND DATA EXTRACTION

Eligible studies met the following criteria: (a) a maternal pregnancy exposure; (b) an outcome assessed in offspring of the pregnancy; and (c) a genetic variant or score proposed as an instrument or proxy for an exposure.

SYNTHESIS

We quantified the frequency of reporting of MR conditions stated, techniques used to examine assumption plausibility, and reported limitations.

RESULTS

Forty-three eligible studies were identified. When discussing challenges or limitations, the most common issues described were known potential biases in the broader MR literature, including population stratification (n = 29), weak instrument bias (n = 18), and certain types of pleiotropy (n = 30). Of 22 studies presenting point estimates for the effect of exposure, four defined their causal estimand. Twenty-four studies discussed issues unique to prenatal MR, including selection on pregnancy (n = 1) and pleiotropy via postnatal exposure (n = 10) or offspring genotype (n = 20).

CONCLUSIONS

Prenatal MR studies frequently discuss issues that affect all MR studies, but rarely discuss problems specific to the prenatal context, including selection on pregnancy and effects of postnatal exposure. Future prenatal MR studies should report and attempt to falsify their assumptions, with particular attention to issues specific to prenatal MR. Further research is needed to evaluate the impacts of biases unique to prenatal MR in practice.

Developing a theoretical evolutionary framework to solve the mystery of parturition initiation

Eutherian mammals have characteristic lengths of gestation that are key for reproductive success, but relatively little is known about the processes that determine the timing of parturition, the process of birth, and how they are coordinated with fetal developmental programs. This issue remains one of biology's great unsolved mysteries and has significant clinical relevance because preterm birth is the leading cause of infant and under 5 year old child mortality worldwide. Here, we consider the evolutionary influences and potential signaling mechanisms that maintain or end pregnancy in eutherian mammals and use this knowledge to formulate general theoretical evolutionary models. These models can be tested through evolutionary species comparisons, studies of experimental manipulation of gestation period and birth timing, and human clinical studies. Understanding how gestation time and parturition are determined will shed light on this fundamental biological process and improve human health through the development of therapies to prevent preterm birth.

Estimating indirect parental genetic effects on offspring phenotypes using virtual parental genotypes derived from sibling and half sibling pairs

Indirect parental genetic effects may be defined as the influence of parental genotypes on offspring phenotypes over and above that which results from the transmission of genes from parents to their children. However, given the relative paucity of large-scale family-based cohorts around the world, it is difficult to demonstrate parental genetic effects on human traits, particularly at individual loci. In this manuscript, we illustrate how parental genetic effects on offspring phenotypes, including late onset conditions, can be estimated at individual loci in principle using large-scale genome-wide association study (GWAS) data, even in the absence of parental genotypes. Our strategy involves creating “virtual” mothers and fathers by estimating the genotypic dosages of parental genotypes using physically genotyped data from relative pairs. We then utilize the expected dosages of the parents, and the actual genotypes of the offspring relative pairs, to perform conditional genetic association analyses to obtain asymptotically unbiased estimates of maternal, paternal and offspring genetic effects. We apply our approach to 19066 sibling pairs from the UK Biobank and show that a polygenic score consisting of imputed parental educational attainment SNP dosages is strongly related to offspring educational attainment even after correcting for offspring genotype at the same loci. We develop a freely available web application that quantifies the power of our approach using closed form asymptotic solutions. We implement our methods in a user-friendly software package IMPISH (IMputing Parental genotypes In Siblings and Half Siblings) which allows users to quickly and efficiently impute parental genotypes across the genome in large genome-wide datasets, and then use these estimated dosages in downstream linear mixed model association analyses. We conclude that imputing parental genotypes from relative pairs may provide a useful adjunct to existing large-scale genetic studies of parents and their offspring.

Indirect parental genetic effects may be defined as the influence of parental genotypes on offspring phenotypes over and above that which results from the transmission of genes from parents to children. Estimating indirect parental genetic effects on offspring outcomes at the genotype level has been challenging because it requires large-scale, individual level genotypes from both parents and their offspring, and there is a paucity of cohorts around the world with this information. Here we present a new approach to estimate indirect parental genetic effects without the requirement of physically genotyped parents. Our method creates virtual parental genotypes based on the genotypes of offspring pairs, and then uses these virtual genotypes in downstream genetic association analyses. We developed a software package “IMPISH” that allows users to impute virtual parental genotypes in their own genome-wide datasets and then use these in downstream genome-wide association analyses, as well a series of power calculators to estimate the power to detect indirect parental genetic effects on offspring phenotypes. We apply our method to educational attainment data from the UK Biobank and show that indirect parental genetic effects are related to offspring educational attainment even after correcting for offspring genotype at the same loci.

Dissecting maternal and fetal genetic effects underlying the associations between maternal phenotypes, birth outcomes, and adult phenotypes: A mendelian-randomization and haplotype-based genetic score analysis in 10,734 mother-infant pairs

BACKGROUND

Many maternal traits are associated with a neonate's gestational duration, birth weight, and birth length. These birth outcomes are subsequently associated with late-onset health conditions. The causal mechanisms and the relative contributions of maternal and fetal genetic effects behind these observed associations are unresolved.

METHODS AND FINDINGS

Based on 10,734 mother-infant duos of European ancestry from the UK, Northern Europe, Australia, and North America, we constructed haplotype genetic scores using single-nucleotide polymorphisms (SNPs) known to be associated with adult height, body mass index (BMI), blood pressure (BP), fasting plasma glucose (FPG), and type 2 diabetes (T2D). Using these scores as genetic instruments, we estimated the maternal and fetal genetic effects underlying the observed associations between maternal phenotypes and pregnancy outcomes. We also used infant-specific birth weight genetic scores as instrument and examined the effects of fetal growth on pregnancy outcomes, maternal BP, and glucose levels during pregnancy. The maternal nontransmitted haplotype score for height was significantly associated with gestational duration (p = 2.2 × 10-4). Both maternal and paternal transmitted height haplotype scores were highly significantly associated with birth weight and length (p < 1 × 10-17). The maternal transmitted BMI scores were associated with birth weight with a significant maternal effect (p = 1.6 × 10-4). Both maternal and paternal transmitted BP scores were negatively associated with birth weight with a significant fetal effect (p = 9.4 × 10-3), whereas BP alleles were significantly associated with gestational duration and preterm birth through maternal effects (p = 3.3 × 10-2 and p = 4.5 × 10-3, respectively). The nontransmitted haplotype score for FPG was strongly associated with birth weight (p = 4.7 × 10-6); however, the glucose-increasing alleles in the fetus were associated with reduced birth weight through a fetal effect (p = 2.2 × 10-3). The haplotype scores for T2D were associated with birth weight in a similar way but with a weaker maternal effect (p = 6.4 × 10-3) and a stronger fetal effect (p = 1.3 × 10-5). The paternal transmitted birth weight score was significantly associated with reduced gestational duration (p = 1.8 × 10-4) and increased maternal systolic BP during pregnancy (p = 2.2 × 10-2). The major limitations of the study include missing and heterogenous phenotype data in some data sets and different instrumental strength of genetic scores for different phenotypic traits.

CONCLUSIONS

We found that both maternal height and fetal growth are important factors in shaping the duration of gestation: genetically elevated maternal height is associated with longer gestational duration, whereas alleles that increase fetal growth are associated with shorter gestational duration. Fetal growth is influenced by both maternal and fetal effects and can reciprocally influence maternal phenotypes: taller maternal stature, higher maternal BMI, and higher maternal blood glucose are associated with larger birth size through maternal effects; in the fetus, the height- and metabolic-risk-increasing alleles are associated with increased and decreased birth size, respectively; alleles raising birth weight in the fetus are associated with shorter gestational duration and higher maternal BP. These maternal and fetal genetic effects may explain the observed associations between the studied maternal phenotypes and birth outcomes, as well as the life-course associations between these birth outcomes and adult phenotypes.

The influence of transmitted and non-transmitted parental BMI-associated alleles on the risk of overweight in childhood

Overweight in children is strongly associated with parental body mass index (BMI) and overweight. We assessed parental transmitted and non-transmitted genetic contributions to overweight in children from the Danish National Birth Cohort by constructing genetic risk scores (GRSs) from 941 common genetic variants associated with adult BMI and estimating associations of transmitted maternal/paternal and non-transmitted maternal GRS with child overweight. Maternal and paternal BMI (standard deviation (SD) units) had a strong association with childhood overweight [Odds ratio (OR): 2.01 (95% confidence interval (CI) 1.74; 2.34) and 1.64 (95% CI 1.43; 1.89)]. Maternal and paternal transmitted GRSs (SD-units) increased odds for child overweight equally [OR: 1.30 (95% CI 1.16; 1.46) and 1.30 (95% CI 1.16; 1.47)]. However, both the parental phenotypic and the GRS associations may depend on maternal BMI, being weaker among mothers with overweight. Maternal non-transmitted GRS was not associated with child overweight [OR 0.98 (95% CI 0.88; 1.10)] suggesting no specific influence of maternal adiposity as such. In conclusion, parental transmitted GRSs, based on adult BMI, contribute to child overweight, but in overweight mothers other genetic and environmental factors may play a greater role.

Variable prediction accuracy of polygenic scores within an ancestry group

Fields as diverse as human genetics and sociology are increasingly using polygenic scores based on genome-wide association studies (GWAS) for phenotypic prediction. However, recent work has shown that polygenic scores have limited portability across groups of different genetic ancestries, restricting the contexts in which they can be used reliably and potentially creating serious inequities in future clinical applications. Using the UK Biobank data, we demonstrate that even within a single ancestry group (i.e., when there are negligible differences in linkage disequilibrium or in causal alleles frequencies), the prediction accuracy of polygenic scores can depend on characteristics such as the socio-economic status, age or sex of the individuals in which the GWAS and the prediction were conducted, as well as on the GWAS design. Our findings highlight both the complexities of interpreting polygenic scores and underappreciated obstacles to their broad use.