Race, intervening variables, and two components of low birth weight.

The low birth weight (LBW) gap between blacks and whites has remained largely unexplained in past research. Most previous research on the topic has focused on LBW as a single entity, and without using a causal framework for analysis. The present study examines the determinants of race differences in the two main components of LBW--preterm birth (PRETERM) and intrauterine growth retardation (IUGR)-within a partially causal framework that includes social and proximate explanatory variables. The data come from the 1988 National Survey of Family Growth. This study asks, first, through what intervening variables do race and other exogenous sociodemographic variables operate to raise the risk of these adverse pregnancy outcomes? Second, what are the determinants of the two components of LBW when all explanatory variables are included in the model? The findings reveal differences in how race (and other exogenous variables) act through downstream variables to affect PRETERM and IUGR, as well as differences in the net determinants of these pregnancy outcomes. The models are better able to account statistically for race differences in IUGR (which is explained by intervening sociodemographic, attitude, and behavior variables) than in PRETERM (which is explained partly by intervening health variables).