Alteration in vaginal microflora, douching prior to pregnancy, and preterm birth.

We aimed to determine the relationship of douching prior to pregnancy and bacterial vaginosis (BV) during pregnancy on preterm birth, addressing individual and joint effects. We used a prospective cohort study and assessed vaginal microflora using gram stains and Nugent's criteria. Douching behaviour was based on self-report about the 12 months prior to pregnancy. Preterm births were categorised as spontaneous or medically indicated. A total of 2561 women provided vaginal specimens and 1492 provided self-reports on douching behaviour. Bacterial vaginosis assessed at 24-28 weeks' gestation in the absence of douching prior to pregnancy was associated with spontaneous preterm birth (odds ratio = 2.74 [95% confidence interval 1.13, 6.66]) as was douching in the absence of BV (OR = 2.20 [1.29, 3.75]). The combination of BV and douching was unrelated to spontaneous or medically indicated preterm birth. We concluded that acute alterations in vaginal microflora at mid-pregnancy or douching prior to pregnancy were associated with an increased risk of preterm birth, but the combination did not appear to increase the risk further than would be expected.