RESUMO
BACKGROUND: Prematurity is considered to be the leading cause of death in children under 5 years of age, with one child dying every 2 s. Smoking is known to be one of the factors associated with prematurity, with both immediate and late consequences. However, it is difficult to obtain concrete data on the relationship between smoking and spontaneous preterm birth. OBJECTIVE: The aim of this study was to evaluate the influence of active and passive smoking on spontaneous preterm birth. METHODS: This was a multicenter, cross-sectional complementary study that included data on preterm births in 20 maternity hospitals in Brazil between 2011 and 2012. The relationship between smoking category (people who smoke [PWS]; people who smoke indirectly [PWSI]; and people who do not smoke [PWDNS]) and sociodemographic characteristics, birth, and neonatal data was assessed. Statistical analysis was performed using frequencies, percentages, the χ2 test, and stepwise comparisons, with a significance level of 5%. RESULTS: The original study included 5295 pregnant participants and their preterm infants. There were 1491 spontaneous preterm births (SPBs); 1191 preterm rupture of membranes; 1468 therapeutic preterm births; and 1146 term births. The proportion of women who were PWS during pregnancy was 13.5%, and 31.6% were PWSI. Pregnant individuals who smoked and who smoked indirectly had a higher incidence of SPBs (61.2%) compared with PWDNS (48.4%; P < 0.0001); however, multivariate analysis did not confirm causality. CONCLUSIONS: This study did not confirm that smoking during pregnancy increases the risk of SPB. PWSI also did not have an increased incidence of spontaneous preterm birth or adverse neonatal outcomes.