Birth Weight and Development: Bias or Heterogeneity by Polygenic Risk Factors?

Exploring the Fetal Origins Hypothesis Using Genetic Data

Birth weight is a robust predictor of valued life course outcomes, emphasizing the importance of prenatal development. But does birth weight act as a proxy for environmental conditions in utero, or do biological processes surrounding birth weight themselves play a role in healthy development? To answer this question, we leverage variation in birth weight that is, within families, orthogonal to prenatal environmental conditions: one's genes. We construct polygenic scores in two longitudinal studies (Born in Bradford, N = 2008; Wisconsin Longitudinal Study, N = 8488) to empirically explore the molecular genetic correlates of birth weight. A 1 standard deviation increase in the polygenic score is associated with an ~100-grams increase in birth weight and a 1.4 pp (22 percent) decrease in low birth weight probability. Sibling comparisons illustrate that this association largely represents a causal effect. The polygenic score-birth weight association is increased for children who spend longer in the womb and whose mothers have higher body mass index, though we find no differences across maternal socioeconomic status. Finally, the polygenic score affects social and cognitive outcomes, suggesting that birth weight is itself related to healthy prenatal development.

Patterns of Co-occurring Developmental Failures in Adolescence: Socioeconomic and Genetic Antecedents and Health Outcomes in Adulthood

This study investigates (1) conjoint latent classes of adolescent co-occurring developmental problems (obesity, depressive symptoms, and low educational attainment), (2) socioeconomic and genetic influences on these classes of adolescents' problem trajectories, and (3) physical health consequences of those latent classes. Data from the National Longitudinal Study of Adolescent to Adult Health (Add Health; N = 9,107; mean age = 15.5 years; Female = 52.9 per cent) were used to identify classes of early socioeconomic adversity and conjoint trajectory groups of co-occurring developmental problems. Profiles of social antecedents, genetic endowments (polygenic scores), and physical health outcomes in young adulthood were compared across identified four conjoint trajectory risk groups (overall high-risk, overall low-risk, BMI-risk or obesity, low education-risk). The results showed that youth with overall high-risk and BMI/education-specific risk trajectory groups were more likely to be Black or Hispanic, reported more adverse socioeconomic characteristics and genetic endowment, and averaged significantly poorer physical health in young adulthood compared with youth in the overall low-risk problem trajectory group. Less pronounced differences emerged between the high-risk and problem-specific-risk groups. The findings highlight heterogeneity in adolescent co-occurring developmental problems. Adolescent heterogeneous problem co-development is associated with background socioeconomic and genetic characteristics and physical health in young adulthood.