Objective: The correlation between periodontal status and systemic conditions, among them pregnancy, is widely described in the scientific literature. The aim of the present systematic review of the literature was to evaluate periodontal diseases as an independent risk factor for adverse pregnancy outcomes. Data: Case-control studies reporting pregnancy outcomes and periodontal status of the subjects were included. Risk of bias evaluation was performed using a tool developed by the Cochrane Bias Methods Group. After risk of bias evaluation of included studies, a meta-analysis was performed computing the Risk Ratio (RR) for each pregnancy outcome. Sources: Electronic databases (MedLine, Embase, Cochrane Central) were searched after preparation of an appropriate search string. Study selection: The search resulted in 422 entries that were screened. After application of inclusion and exclusion criteria, a total of 22 studies were included in the review accounting for a total of 17,053 subjects. The computed RR for periodontitis was 1.61 for preterm birth evaluated in 16 studies (P .001), 1.65 for low birthweight evaluated in 10 studies (P .001), and 3.44 for preterm low birthweight evaluated in four studies. Conclusion: The present systematic review reported a low but existing association between periodontitis and adverse pregnancy outcomes. This assumption is the result of proper corrections of biased methodologies and of heterogeneity of studies. ( Keywords: adverse pregnancy outcomes, meta-analysis, periodontal diseases, periodontitis, risk factor