['The purpose of this study was to test whether treating periodontal disease (PD) in pregnancy will reduce the incidence of spontaneous preterm delivery (SPTD) at < or = 35 weeks of gestation.', 'A multicenter, randomized clinical trial was performed. Subjects with PD were randomized to scaling and root planing (active) or tooth polishing (control). The primary outcome was the occurrence of SPTD at <35 weeks of gestation.', 'We screened 3563 subjects for PD; the prevalence of PD was 50%. Seven hundred fifty-seven subjects were assigned randomly; 378 subjects were assigned to the active group, and 379 subjects were assigned to the placebo group. Active treatment did not reduce the risk of SPTD at <35 weeks of gestation (relative risk, 1.19; 95% confidence interval [CI], 0.62-2.28) or composite neonatal morbidity (relative risk, 1.30; 95% CI, 0.83-2.04). There was a suggestion of an increase in the risk of indicated SPTD at <35 weeks of gestation in those subjects who received active treatment (relative risk, 3.01; 95% CI, 0.95-4.24).'] Does treatment of localized periodontal disease in pregnancy reduce the occurrence of preterm birth : results from the Periodontal Infections and Prematurity Study ( PIPS )?