Periodontitis has been associated with adverse pregnancy outcomes. Results from intervention studies are few and controversial. The present study assessed the effects of non-surgical periodontal treatment in the occurrence of adverse pregnancy outcomes. Two hundred forty-six eligible women were randomly divided into two groups: periodontitis intervention (n = 122; undergoing non-surgical treatment during gestation) and periodontitis control (n = 124; not treated during gestation). Univariate analysis was performed and estimates of relative risk were reported. Data from 225 women were analyzed. No differences for preterm birth (p = 0.721), low birth weight (p = 0.198), and preterm low birth weight (p = 0.732) rates were observed. Relative risk estimates for preterm birth, low birth weight, and preterm low birth weight in the periodontitis intervention group were 0.915 (95% CI 0.561-1.493), 0.735 (95% CI 0.459-1.179), and 0.927 (0.601-1.431), respectively. Non-surgical periodontal treatment during the second semester of gestation did not reduce the risk for preterm birth, low birth weight, and preterm low birth weight.