Recurrence of preterm births: a population-based linkage with 3.5 million live births from the CIDACS Birth Cohort

OBJECTIVE: To investigate the recurrence of preterm birth (PTB) among the poorest half of the Brazilian population. METHODS: We conducted a population-based retrospective study in Brazil with the live births of multiparous women extracted from the CIDACS Birth Cohort between 2001 and 2015. We used multivariate logistic regression to estimate the odds of recurrent PTB in second and third births. RESULTS: A total of 3,528,050 live births from 1,764,025 multiparous women were analyzed. The adjusted odds for the occurrence of a PTB given a previous PTB was 2.58 (95% CI 2.53-2.62). Lower gestational age increased the odds of a subsequent PTB [(aOR <28 weeks 3.61, 95% CI 3.41-3.83), (aOR 28 to 31 weeks 3.34, 95% CI 3.19-3.49), (aOR 32 to 36 weeks 2.42, 95% CI 2.38-2.47)]. Women who had two previous PTBs were at high risk of having a third (aOR 4,98 IC 95% 4.70-5.27). Recurrence of a PTB was more likely when the inter-birth interval was less than 12 months. CONCLUSIONS: In Brazil, a middle-income country, women with a previous PTB had an increased risk of a subsequent one. This association was affected by gestational age, the number of PTBs, severity of previous PTBs, and a short interval between births.