Racial differences in the relation of birth weight and gestational age to neonatal mortality.

Utilizing South Carolina live birth-infant death cohort files for the period 1975-80, this study examines the bivariate distribution of birth weight-gestational age (BW-GA), intrauterine growth curves, and BW-GA specific neonatal mortality rates (NMRs) by race. Comparison of BW-GA distributions revealed an appreciable shift between racial subgroups. Nonwhites, on the average, were born 1 week earlier and 270 grams lighter in weight than whites. In addition to racial differences in rates of intrauterine growth, nonwhites experienced lower BW-GA NMRs than whites in BW-GA categories less than 3,000 grams and less than 38 weeks. However, the improved mortality experience of nonwhites at more immature BW-GA categories was not consistently present when different cause-specific NMRs were considered. These persistent racial variations highlight continuing issues regarding both the use of a single norm for defining low birth weight or prematurity and the role of nonsocioeconomic factors related to racial BW-GA distribution and mortality disparities. As birth weight and gestational age represent empirical indicators of the maturity and survivability of an infant at birth, these data and previous supporting research raise further concerns regarding the ability of these indicators to accurately reflect equivalent fetal development and subsequent risk of mortality among racial groups.