Determinants of preterm birth: Pelotas 2004 birth cohort

Introduction: Prematurity is a leading cause of neonatal death. Preterm birth is a global health problem that affects high, middle and low-income countries. Increase in preterm birth has been reported in Brazil, leading to a rising trend in the prevalence of low birth weight babies, and also may have had contributed to the lack of success in reducing neonatal mortality. In our cohort data, there is a high frequency of obstetric interventions among the rich, whereas the poor are more likely to present urinary and genital infections. We test the hypothesis that different risk factors determine preterm birth in different income groups by investigating whether risk factors vary among these groups.
Methods: From January to December 2004, a birth cohort study recruited all hospital births. Newborns were examined and mothers were interviewed soon after delivery using a pre-tested structured questionnaire. Information was obtained on demographic, socioeconomic, behavioral and biological characteristics, reproductive history and health care utilization. A total of 4,142 women were included in the analysis.
Results: In the multivariate analysis black skin color, low education, poverty, young maternal age, primiparity, previous preterm birth, absence of prenatal care, and reported hypertension remained significantly associated with preterm birth. In the analyses repeated after stratification by family income terciles there was no evidence of effect modification by income and no clear patterns differences between the socioeconomic groups emerged. No association between cesarean section and preterm delivery was found.
Discussion: Further studies are required to understand the causes for the epidemic of preterm births in Brazil. These studies, unlike our own, should recruit women during pregnancy and use laboratory tests and physical examination to document morbidity in a more reliable way. Better documentation of indications for medical interventions such as induction and cesarean sections is also needed.