Merchant AT, et al. - Given that the Obstetrics and Periodontal Therapy (OPT) study, a randomized controlled trial, reported no effect of periodontal treatment on preterm birth despite more spontaneous abortions or stillbirths in the control group, experts assessed the impact of the periodontal treatment on preterm birth. They utilized the survivor average causal effect (SACE), also known as the principal strata effect, to correct potential bias resulting from unequal survival of fetuses in the treatment and control arms of the OPT study. As per data, preterm births could be prevented by periodontal treatment provided to mothers with mild to moderate periodontal disease before 21-weeks of gestation. In the periodontal treatment group, the risks of preterm and spontaneous abortions or stillbirths were 11.86% and 1.21 % respectively, and 12.68% and 3.33% respectively in the control group.