Birth weight and cognitive development in adolescence: causal relationship or social selection?

Birth Weight and Early Cognitive Skills: Can Parenting Offset the Link?

Objectives There is an enduring negative association between low birth weight (<2500 g) and early childhood cognitive skills. This study examines if parenting practices meaningfully contribute to or offset birth weight disparities in cognitive development prior to formal schooling. Methods This study uses the ECLS-B, a nationally representative sample of live births in the United States in 2001. Unlike studies focused on one or two measures of parenting and investment, this study considers a wide array parenting measures collected at multiple time points, tracked from before birth across 5 years of development. Results Regression results show that nearly 50 % of the low-birth-weight gap in early math and reading ability is associated with family socioeconomic status. Between-family OLS regressions show that parenting practices, including "parental interaction," "cognitive stimulation," and "parent quality", are negatively associated with low birth weight and positively associated with improved cognitive skill among all children. After adjustment for family socioeconomic status, parenting practices did little to offset (by mediation or moderation) remaining birth weight disparities in early cognitive development. Conclusions Effective parenting is positively associated with cognitive development, but parenting is not a panacea-the developmental disadvantages associated with poor child health are not linked to parenting practices. We argue that birth weight disparities are rooted in biology and cannot easily be offset by parenting practices.

The association of high birth weight with intelligence in young adulthood: a cohort study of male siblings

We aimed to explore why, in population studies, the positive association between normal-range birth weight and intelligence becomes negative at the highest birth weights. The study population comprised 217,746 Norwegian male singletons born at term between 1967 and 1976. All had data on birth weight and intelligence quotient (IQ) score at the time of military conscription; 137,574 had data on sibling birth weights; and 62,906 had data on male sibling birth weights. We estimated associations between birth weight and IQ score by ordinary least squares regression for the total study population and by fixed-effects regression for comparisons of brothers. The crude mean IQ score was 1.2 points (95% confidence interval (CI): 0.3, 2.2) lower for those with birth weights of 5,000 g or more compared with the reference group (with birth weights of 4,000-4,499 g). This difference leveled off to 0.0 (95% CI: -0.8, 0.9) in multivariable ordinary least squares regression and reversed to 2.2 points (95% CI: 0.3, 4.2) higher in fixed-effects regression. Results differed mainly because, at a given birth weight, participants who had a sibling with macrosomia had a lower mean IQ score. Nevertheless, within families with 1 or more macrosomic siblings, as in other families, men with higher birth weights tended to have higher IQ scores. Thus, a family-level confounder introduces a cross-level bias that cannot be detected in individual-level studies. We suggest ways in which future studies might elucidate the nature of this confounder.

Childbearing postponement and child well-being: a complex and varied relationship?

Over the past several decades, U.S. fertility has followed a trend toward the postponement of motherhood. The socioeconomic causes and consequences of this trend have been the focus of attention in the demographic literature. Given the socioeconomic advantages of those who postpone having children, some authors have argued that the disadvantage experienced by certain groups would be reduced if they postponed their births. The weathering hypothesis literature, by integrating a biosocial perspective, complicates this argument and posits that the costs and benefits of postponement may vary systematically across population subgroups. In particular, the literature on the weathering hypothesis argues that, as a consequence of their unique experiences of racism and disadvantage, African American women may experience a more rapid deterioration of their health which could offset or eventually reverse any socioeconomic benefit of postponement. But because very few African American women postpone motherhood, efforts to find compelling evidence to support the arguments of this perspective rely on a strategy of comparison that is problematic because a potentially selected group of older black mothers are used to represent the costs of postponement. This might explain why the weathering hypothesis has played a rather limited role in the way demographers conceptualize postponement and its consequences for well-being. In order to explore the potential utility of this perspective, we turn our attention to the UK context. Because first-birth fertility schedules are similar for black and white women, we can observe (rather than assume) whether the meaning and consequences of postponement vary across these population subgroups. The results, obtained using linked UK census and birth record data, reveal evidence consistent with the weathering hypothesis in the United Kingdom and lend support to the arguments that the demographic literature would benefit from integrating insights from this biosocial perspective.

Understanding links between adolescent health and educational attainment

The educational and economic consequences of poor health during childhood and adolescence have become increasingly clear, with a resurgence of evidence leading researchers to reconsider the potentially significant contribution of early-life health to population welfare both within and across generations. Meaningful relationships between early-life health and educational attainment raise important questions about how health may influence educational success in young adulthood and beyond, as well as for whom its influence is strongest. Using data from the National Longitudinal Survey of Youth 1997, I examine how adolescents'health and social status act together to create educational disparities in young adulthood, focusing on two questions in particular. First, does the link between adolescent health and educational attainment vary across socioeconomic and racial/ethnic groups? Second, what academic factors explain the connection between adolescent health and educational attainment? The findings suggest that poorer health in adolescence is strongly negatively related to educational attainment, net of both observed confounders and unobserved, time-invariant characteristics within households. The reduction in attainment is particularly large for non-Hispanic white adolescents, suggesting that the negative educational consequences of poor health are not limited to only the most socially disadvantaged adolescents. Finally, I find that the link between adolescent health and educational attainment is explained by academic factors related to educational participation and, most importantly, academic performance, rather than by reduced educational expectations. These findings add complexity to our understanding of how the educational consequences of poor health apply across the social hierarchy, as well as why poor health may lead adolescents to complete less schooling.

Reproducing inequalities: luck, wallets, and the enduring effects of childhood health

In this article, I argue that research on social stratification, on intergenerational transmission of inequalities, and on the theory of factor payments and wage determination will be strengthened by studying the role played by early childhood health. I show that the inclusion of such a factor requires researchers to integrate theories in each of these fields with new theories linking early childhood health conditions and events that occur at later stages in the life course of individuals, particularly physical and mental health as well as disability and mortality. The empirical evidence I gather shows that early childhood health matters for the achievement of or social accession to, adult social class positions. Even if the magnitude of associations is not overwhelming, it is not weaker than that found between adult social accession and other, more conventional and better-studied individual characteristics, such as educational attainment. It is very likely that the evidence presented in this article grossly underplays the importance of early childhood health for adult socioeconomic achievement.

Growth in early life and childhood IQ at age 11 years: the Newcastle Thousand Families Study

BACKGROUND

It has been suggested that in addition to genetic factors, fetal and post-natal growth influence childhood cognition, although it is unclear whether such an effect continues throughout childhood. This study aimed at investigating the potential relationships between childhood IQ at age 11 years and birth weight and height at the ages of 9 and 13 years, after adjusting for the confounding factors available to this investigation.

METHODS

The Newcastle Thousand Families study, a prospectively followed cohort, originally consisted of all 1142 births in the city of Newcastle in May and June 1947. Using data on 733 members of this cohort, we investigated the associations between IQ at age 11, and birth weight and height at ages 9 and 13 years.

RESULTS

Birth weight showed no association with childhood IQ. However, height at age 9 years was a significant predictor of childhood IQ after adjusting for socioeconomic status (standardized regression coefficient b = 2.6, 95% CI 1.6-3.6, P < 0.0001). Height at age 13 was also a significant predictor of IQ after adjusting for socioeconomic status (b = 3.4, 95% CI 2.3-4.4, P = 0.001), and explained an additional 2.5% of the variation in IQ scores to that already explained by socioeconomic status and height at age nine.

CONCLUSIONS

These results suggest a continuing effect of post-natal growth on childhood cognition beyond the age of 9 years. Post-natal growth, which may be influenced by genetic factors and nutrition and socioeconomic circumstances in childhood, may be more important than fetal growth in terms of childhood cognition.