Factors associated with premature birth: a case-control study

OBJECTIVE: To analyze the socioeconomic, demographic, environmental, reproductive, behavioral, and health-care factors associated with preterm birth. METHODS: Case-control study, with case group composed of preterm infants and the control group by full term live births. Each case was paired with two controls according to sex and date of birth. Interviews were carried out with the mothers, as well as analysis of medical records. A logistic regression model was used for data analysis following the hierarchical order of entry of the blocks. RESULTS: 221 live births were allocated in the case group and 442 in the control group. After analysis adjusted for other factors under study, the highest chances of prematurity were associated with being the first child (OR 1.96; 95%CI 1.34–2.86; p=0.001); mothers with the highest income (OR 2.08; 95%CI 1.41–3.08; p<0.001), mothers with previous preterm births (OR 3.98; 95%CI 2.04–7.79; p<0.001), mothers that suffered violence during pregnancy (OR 2.50; 95%CI 1.31–4.78; p=0.005) and underwent cesarean section (OR 2.35; 95%CI 1.63–3.38; p<0.001). Live births to mothers who had more than six prenatal consultations had a lower risk of prematurity (OR 0.39; 95%CI 0.26–0.58; p<0.001). CONCLUSIONS: The factors associated with a higher chance of prematurity were: higher family income, previous preterm child, primiparity, violence against pregnant women and cesarean section. Having attended more than six prenatal visits was associated with a lower chance of premature birth. Violence against pregnant women showed a strong and consistent association, remaining in all final models, and should serve as an alert for the population and professionals.