[Birth weight intra-urban differentials in the city of São Paulo].

OBJECTIVE To identify intra-urban differentials and risk factors in low birth weight prevalence. METHODS Information was gathered in the live birth declarations made by mothers residing in the city of São Paulo (Southern Brazil), and obtained through the Live Birth Information System and the Seade Foundation, for the period between 2002 and 2003, totaling 388,980 live births. The addresses were georeferenced in census tracts and classified into six vulnerability groups according to the São Paulo State Social Vulnerability Index. To identify potential risk factor logistic regression analysis was performed. RESULTS A positive growth trend was observed in the prevalence of low birth weight with an increase in the vulnerability rate (from 6.8% to 8.1%). There were significant differences among groups in terms of mothers' demographics, prenatal care and the proportion of non-preterm low weight births. In the low birth weight non-preterm group, a proxy measure to estimate intra-uterine growth delay, residing in vulnerable areas (1.29;1.17-1.43) and unfavorable mothers' demographics, such as teenage mothers (1.13;1.04-1.22), low schooling (1.26;1.17-1.35) and high number of children (1.10;1.01-1.20) were considered risk factors, as were older mothers (1.38;1.30-1.47), and single mothers (1.15;1.11-1.20). The lack of prenatal care produced the highest risk of low weight at birth in preterm (3.39;2.86-4.02) and non-preterm births (2.12;1.87-2.41). There was a decrease in the risk for low birth weight with an increase in prenatal care appointments in preterm and non-preterm births. CONCLUSIONS There are low birth weight prevalence differences across vulnerability groups. Prenatal care proved to be unequal across vulnerability groups and its high risk in terms of low birth weight shows the importance of increasing the access to and the quality of healthcare services.