Racial differences in birth health risk: a quantitative genetic approach.

In the United States the gap between black and white babies' birth weights has remained largely unexplained. Rather than trying to measure all relevant variables, we used a genetically informative design to study the relative importance of genetic and environmental factors. Employing multiple indicators of "birth health risk," we found that the racial differences increased with the magnitude of the shared environmental effects. This suggested that possible genetic effects would not pertain to fetal genes, although genes affecting the mother's physical or physiological characteristics could be important because they contribute to shared environment in our analysis.