BACKGROUND: Although neonatal mortality has been declining in the City of São Paulo, it still is an important public health problem. Four basic categories constitute risk factors: newborn characteristics, maternal characteristics, socio-economic conditions and quality of health care. Low birth weight and prematurity are the dominant factors and constitute a complex network with other factors. METHODS: A case-control study was carried out based on linked birth and death certificates of the City of São Paulo for the first semester of 1995. The study performed a hierarchical analysis, considering four blocks of variables (characteristics of the new-born; mothers, health care and socio-economic status) for all birth-weight groups together and separately for three birth-weight groups: <1,500g, 1,500-2,499g and >2,500g. RESULTS: The final model for all newborns together showed statistical significant association for mothers under 20 years of age, being born in a SUS hospital, birth weight <2,500g and prematurity. The three birth weight groups showed distinctive patterns of risk factors. Those <1,500g had lower mortality when born in a university hospital and caesarean section. The 1,500-2,499g group had increased risk for mortality with prematurity, male sex and high parity of mother. In the more than 2,500g group, risk factors for mortality were prematurity, adolescent mother, living in an area with low quality of life, being born in a SUS hospital and caesarean section. CONCLUSION: This study, while pointing out the enormous influence of low birth weight on neonatal mortality in São Paulo, demonstrated that different birth weight categories have distinct biological and social vulnerabilities with complex links, and that health services have an important role to play for each of them.
Neonatal mortality; Birth weight; Socioeconomic risk factors; Socioeconomic health services
