Vaginal douching, bacterial vaginosis, and spontaneous preterm birth.

Objective: Vaginal douching and bacterial vaginosis (BV) are independently associated with spontaneous preterm birth. Because the interrelationships among these variables remain unclear, we sought to examine the associations in a prospective study.

Methods: We conducted a nested case-control study within a prospectively recruited cohort of pregnant women. We prospectively collected demographic and health status data, data on pre-pregnancy vaginal douching, vaginal smears for bacterial vaginosis as defined by Nugent's criteria, fetal fibronectin at 26 weeks of pregnancy, and placental pathology at delivery. Spontaneous preterm births before 37 weeks' gestation were selected as cases. All spontaneous births occurring after 37 weeks were potential control subjects. To limit costs, some tests were performed only in selected control subjects.

Results: Preterm birth occurred in 207 of 5092 women (4.1%). In bivariate analysis, BV was not associated with preterm birth (OR 1.2; 95% CI 0.5 to 2.4). Vaginal douching was significantly associated with bacterial vaginosis (P < 0.05) and preterm birth (P < 0.05). On multivariate analysis, vaginal douching was no longer associated with preterm birth, but a significant association with early preterm birth < 34 weeks (OR, 6.9; 95% CI 1.7 to 28.2) and preterm birth due to preterm labour (OR 3.0; 95% CI 1.1 to 8.5) persisted after controlling for the presence of bacterial vaginosis and placental inflammation.

Conclusion: Vaginal douching and bacterial vaginosis were not associated with spontaneous preterm birth overall. However, vaginal douching appears to be an independent and potentially modifiable risk factor for early preterm birth (32-34 weeks), although the mechanism remains unclear.