Abstract
Preterm birth is more prevalent in African Americans than European Americans and contributes to 3.4 times more African American infant deaths. Models of social inequity do not appreciably account for this marked disparity and molecular genetic studies have yet to characterize whether allelic differences that exist between races contribute to this gap. In this study, biometrical genetic models are applied to a large mixed-race sample consisting of 733,339 births to measure the extent that heritable factors and environmental exposures predict the timing of birth and explain differences between racial groups. Although we expected significant differences in mean gestational age between racial groups, we did not anticipate the variance of gestational age in African Americans (σ2 = 7.097) to be nearly twice that of European Americans (σ2 = 3.764). Our results show that this difference in the variance of gestational age can largely be attributed to environmental sources; which were 3.1 times greater in African Americans. Specifically, environmental factors that change between pregnancies, versus exposures that influence all pregnancies within a family, are largely responsible for the increased reproductive heterogeneity observed in African American mothers. Although the contribution of both fetal and maternal genetic factors differed between race categories, genetic studies may best be directed to understanding the differences in the socio-cultural sources of this heterogeneity, and their possible interaction with genetic differences within and between races. This study provides a comprehensive description of the relative genetic and environmental contributions to racial differences in gestational age.
Highlights
Preterm birth, defined as delivery before 37 weeks of complete gestation, is a major cause of perinatal mortality and morbidity
Previous preterm birth associated with an increased odds of 5.9 (95% C.I. = 4.1, 8.6) for a subsequent preterm birth [7], may involve fetal and maternal genetic sources that are shared in successive births, and environmental exposures common to all pregnancies of individual mothers
The maximum likelihood estimate of variance in gestational age for African Americans was 7.097, almost twice as large as that observed for European Americans (s2 = 3.764)
Summary
Preterm birth, defined as delivery before 37 weeks of complete gestation, is a major cause of perinatal mortality and morbidity. The difference in prevalence of preterm birth observed between self-reported African American and European American race (17.8% and 11.5% respectively) remains largely unexplained and contributes to 3.4 times more African American infant deaths [2]. While salient risk factors for preterm birth have been indentified, ambiguity about the overall contribution of genetic and environmental sources remains. Previous preterm birth associated with an increased odds of 5.9 = 4.1, 8.6) for a subsequent preterm birth [7], may involve fetal and maternal genetic sources that are shared in successive births, and environmental exposures common to all pregnancies of individual mothers. The increased risk associated with self-identified African American race
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