Vaginal flora in postmenopausal women: the effect of estrogen replacement

To determine the effect of estrogen replacement therapy (ERT) on the vaginal flora of postmenopausal women.

Vaginal cultures were obtained from 15 postmenopausal women whose hormonal statuses were documented by serum follicle-stimulating hormone (FSH) and serum estrogen levels. After 8 weeks of ERT, consisting of 0.1 mg of estradiol delivered daily by dermal patch, the vaginal cultures were repeated, as were measurements of the vaginal pH, serum FSH, and serum estrogen levels.

Vaginal cultures revealed no significant change in the incidence of lactobacilli or of all aerobes. However, the incidence of anaerobic species fell after treatment from 47% to 13% (P = 0.05), and the incidence of anaerobic gram-negative rods declined after treatment from 40% prior to ERT to 7% (P = 0.035). Prior to ERT, the difference in mean vaginal pH between lactobacilli-positive and lactobacilli-negative subjects was not significant, but, following the administration of exogenous estrogen, the lactobacilli-positive subjects exhibited a significantly lower mean vaginal pH (4.4 +/- 0.4) relative to the lactobacilli-negative population (5.2 +/- 0.3) (P = 0.02).

We conclude that women on ERT are less likely to have vaginal colonization with anaerobic bacteria when compared with women not using replacement therapy. Estrogen replacement may potentiate the effect of lactobacilli on vaginal pH.