Trends in preterm birth: results from five population-based surveys in the extreme south of Brazil.

This study aimed to analyze trends in preterm birth in Southern Brazil, and to identify associated maternal characteristics with this outcome. In five cross-sectional surveys, we included all 10,582 puerperal women residing in Rio Grande who had a single birth at years 2007, 2010, 2013, 2016 and 2019. A questionnaire was applied up to 48 hours after delivery. The prevalence of preterm birth (< 37 weeks of gestation) was presented according to maternal characteristics and year of study. We observed a reduction in preterm births, from 17.3% in 2007 to 15.5% in 2019 (-1.8 percentage points (p.p.)). The most expressive reduction was observed among women who gave birth in the private sector (-12.3 p.p.) and those with gestational diabetes (-10.3 p.p.). The risk of having a preterm birth was significantly higher for older women, with black skin color, lower education, multiparous, and those with hypertension, diabetes, and depression during pregnancy. Between 2007 and 2019, there was a reduction in preterm births for most identified risk groups, except for women with low education, depression, and diabetes. Despite the slight reduction in the preterm birth rate over time, this outcome continues to grow in some risk groups.