To systematically review the randomized controlled trials that evaluated the effect of periodontal therapy on preterm birth and low birth weight (LBW). A systematic search was conducted of the PubMed, Bireme, LILACS, and Cochrane databases. Only randomized controlled trials on the effect of periodontal therapy on preterm birth and LBW were included. The Consolidated Standards of Reporting Trials statement was used in quality assessment and meta-analysis was carried out using random-effects methods. The search resulted in 14 clinical studies. Ten articles met the inclusion criteria for preterm birth and four for LBW. Five meta-analyses on preterm birth were performed according to different criteria: 1) use of probing depth and attachment loss for periodontitis definition, relative risk (RR) 0.58 (95% confidence interval [CI] 0.29-1.12) (four studies); 2) controlling for multiparity, RR 0.92 (95% CI 0.72-1.17) (eight studies); 3) controlling for previous preterm birth, RR 0.88 (95% CI 0.67-1.16) (seven studies); 4) controlling for genitourinary infections, RR 0.75 (95% CI 0.57-1.05) (six studies); and 5) all the previous criteria, RR 0.63 (95% CI 0.32-1.22) (three studies). Three meta-analysis on LBW were conducted according to controlling for multiparity, RR 1.03 (95% CI 0.76-1.40) (four studies); controlling for previous preterm birth, RR 0.93 (95% CI 0.65-1.30) (three studies); and use of probing depth and attachment loss for periodontitis definition, controlling for multiparity, previous preterm birth, and genitourinary infections, RR 0.52 (95% CI 0.10-2.60) (two studies). In all meta-analyses, the effect of periodontal treatment on preterm birth and LBW was not statistically significant. Results of this meta-analysis do not support the hypothesis that periodontal therapy reduces preterm birth and LBW indices.