[Consequences of sociodemographic inequalities on birth weight]

To analyze sociodemographic inequalities in prenatal and childbirth care and their consequences on birth weight.

The study was based on a sample of 10,072 postpartum women treated at public (those outsourced by the National Health System) and private maternity hospitals in Rio de Janeiro, Brazil, from 1999 to 2001. To test the association between birth weight and maternal sociodemographic and biological characteristics and prenatal care (modified Kotelchuck index), postpartum women were stratified by level of schooling and two multiple linear regressions were performed. The bootstrap technique was used in addition to accurate confidence intervals for the estimated effects.

For nearly all of the variables analyzed in the bivariate analysis, birth weight was lower among children of mothers with low schooling. In the multivariate analysis, among women with low schooling, there was a direct association between birth weight and the modified Kotelchuck index and gestational age. The variables black skin color, smoking, and history of premature birth were negatively associated with birth weight, while maternal age and parity showed distinct behaviors from the central range of data at the extremes. In the group with high schooling, only parity, gestational age, and modified Kotelchuck index were significant and directly associated with birth weight. The protective effect of prenatal care was observed, as well as the negative effect of smoking, regardless of the mother's level of schooling.

The variables associated with neonates' birth weight of mothers with high schooling in Rio de Janeiro were biological, in contrast to the social determinants in the group with low schooling.