Background: Controversy exists regarding the benefits of treating bacterial vaginosis (BV) during pregnancy to reduce the incidence of preterm labor (PTL). Objectives:To evaluate whether treatment of BV with vaginal clindamycin or oral metronidazole before 28 weeks of pregnancy reduces PTL incidence.Search strategy: PubMed, Scopus, Web of Science, Science Direct, CENTRAL, and SciELO databases were searched until December 30, 2017. Search terms included "bacterial vaginosis" and "preterm labor." No language restrictions were applied. Selection criteria:Randomized clinical trials that evaluated treatment of BV with clindamycin or metronidazole to reduce PTL incidence. Data collection and analysis:The risk of PTL was evaluated by the odds ratio (OR) and 95% confidence interval (CI). Dichotomous data from each study were combined for meta-analysis using the Mantel-Haenszel model. Main results:Nine reports were included in the systematic review, with eight reports included in the meta-analysis. No reduction in the incidence of PTL was found for either metronidazole (OR 0.94, 95% CI 0.71-1.25) or clindamycin (OR 1.01, 95% CI 0.75-1.36).Conclusions: Use of oral metronidazole or vaginal clindamycin to treat BV before 28 weeks of pregnancy did not reduce the incidence of PTL.