The events leading to preterm birth are still not completely understood. A quantitative systematic review was performed to estimate the effects of periodontal care during pregnancy on preventing preterm birth and low birth weight. The meta-analysis included randomized trials with pregnant women with a diagnosis of periodontal disease before 20 weeks of gestation. Relative risk (RR) with 95% confidence intervals (95%CI) was calculated. We evaluated the reduction in preterm and low birth weight. Thirteen trials were included, comparing 3,576 women in intervention groups with 3,412 women receiving usual care. The meta-analysis of the effects of periodontal disease treatment during pregnancy indicated a non-significant reduction in preterm births (RR = 0.90; 95%CI: 0.68-1.19) and low birth weights (RR = 0.92; 95%CI: 0.71-1.20). The creation and examination of a funnel plot revealed clear evidence of publication bias. In summary, primary periodontal care during pregnancy cannot be considered an efficient way of reducing the incidence of preterm birth.