The Impact of Local Estrogen on the Urogenital Microbiome in Genitourinary Syndrome of Menopause: A Randomized-Controlled Trial

Importance The postmenopausal urinary bladder microbiome is not well defined. Objectives The aims of this study were to characterize the effect of vaginal estrogen on the vaginal and urinary bladder microbiome in postmenopausal women and describe any clinical associations with the symptoms of genitourinary syndrome of menopause. Study Design This was a participant-masked, randomized controlled trial comparing the effect of a 12-week course of an estrogen-containing vaginal ring to a placebo vaginal ring. Standardized evaluations were performed at baseline and 12 weeks. Vaginal samples were obtained for pH, vaginal maturation index, and microbiome analysis. Concomitant catheterized urine samples were obtained for microbiome analysis. 16S ribosomal RNA gene sequencing was performed to characterize the resident microbial communities, with Lactobacillus relative abundance as the primary outcome variable. Genitourinary syndrome of menopause symptoms was measured using validated questionnaires (Pelvic Floor Distress Inventory-Short Form, Female Sexual Function Index, Vulvovaginal Symptoms Questionnaire). Results Of the 39 postmenopausal women randomized, baseline characteristics were similar between arms, with a mean age of 62 years and mean vaginal pH of 5.0. Using intention-to-treat analysis, there were no significant changes in vaginal or urinary Lactobacillus relative abundance. Two participants in each arm removed their ring prior to the end of the study. Eighty percent of participants experienced at least 1 bothersome genitourinary syndrome of menopause symptom. Vulvovaginal dryness and urinary frequency were most common at baseline, whereas painful intercourse and urinary urgency were most common at the final visit, none of which were statistically significant. Conclusions Our study did not show a significant change in the bacterial composition of the vaginal or urinary bladder microbiome after either vaginal ring in this relatively asymptomatic postmenopausal population.