Acquisition and elimination of bacterial vaginosis during pregnancy: a Danish population-based study.

Objectives: the aim was to examine factors associated with acquisition and elimination of bacterial vaginosis in pregnancy.

Methods: a group of 229 pregnant women were randomly selected from a population-based prospective cohort study of 2927. They were examined at enrollment (mean gestational weeks 16w+0d) and again in mid-third trimester (mean gestational age 32w+3d).

Measures: BV (Amsel's clinical criteria), microbiological cultures of the genital tract and questionnaire data.

Results: BV prevalence decreased from 17% in early second trimester to 14% in mid-third trimester due to a tenfold higher elimination rate (39%) than incidence rate (4%). Heavy smokers (>10/d) in early pregnancy were at increased risk (5.3[1.1-25]) for the acquisition of BV during pregnancy, as were women receiving public benefits (4.8[1.0-22]), having a vaginal pH above 4.5(6.3[1.4-29]) or vaginal anaerobe bacteria (18[2.7-122]) at enrollment. A previous use of combined oral contraceptives was preventive for the acquisition of BV (0.2[0.03-0.96]). Elimination of BV in pregnancy tended to be associated with a heavy growth of Lactobacillus(3.2[0.8-13]) at enrollment.

Conclusions: acquisition of BV during pregnancy is rare and is associated with smoking, while the presence of anaerobe bacteria and a vaginal pH >4.5 are interpreted as steps on a gradual change towards BV. In the same way heavy growth of Lactobacillus spp in early pregnancy may be an indicator of women on the way to eliminate BV.