The interaction effect of bacterial vaginosis and periodontal disease on the risk of preterm delivery.

The objective of this article is to determine if coexistence of periodontal disease (PD) and bacterial vaginosis (BV) is synergistic on the risk of spontaneous preterm delivery (sPTD). The study design was secondary analysis of a prospective cohort study. Women were screened 6 to 20 weeks gestation for PD and BV. Groups were defined by presence of BV and stratified on PD. The primary outcome was sPTD <37 weeks gestation. Univariable, stratified, and multivariable analyses were performed to estimate the main and interaction effects of BV and PD on sPTD. Of 1453 women screened, 792 (54.5%) were diagnosed with BV. Neither women with BV in the first trimester nor PD was at higher risk of sPTD (risk ratio [RR] for BV 1.1; 95% confidence interval (CI), 0.8-1.5, and RR for PD 0.9; 95% CI, 0.7-1.3). The interaction between BV and PD did not statistically significantly impact the odds of sPTD. Coexistence of PD and BV did not have a synergistic effect on sPTD.