The role of the vaginal microbiome in pregnancy loss and preterm birth: a commentary.

backgroundEubiosis or dysbiosis of the vaginal microbiome may influence the rate of pregnancy loss and preterm birth, the major cause of neonatal and perinatal mortality worldwide.

methodsThis was a comparison of two vaginal microbiome studies; one a cohort study and the other a multinational randomised controlled feasibility study. Both studies used cultivation-independent molecular microbiological techniques that together have implications on the risk of pregnancy loss and preterm birth in association with vaginal dysbiosis.

resultsThe cohort study identified a risk-associated vaginal microbiome signature in association with early pregnancy-loss that comprised an increase in the relative abundance of potentially dysbiotic organisms such as Lactobacillus iners, Sneathia and Prevotella spp and a concomitant decrease in the abundance of eubiotic microorganisms such as Lactobacillus crispatus. Convergent evidence across the two studies demonstrated that a synbiotic intervention was able to shift the vaginal microbiome from the signature demonstrated by Skafte-Holm et al., to a decrease in the abundance of Prevotella, Gardnerella and Atopobium spp, while simultaneously increasing the abundance of eubiotic vaginal Lactobacillus spp.

conclusionsWe concluded that there is convergent evidence across the two studies which might otherwise have gone unnoticed. While neither study was powered to demonstrate clinical endpoints and did not establish causal relationships between microbiome modulation and pregnancy outcomes, when administered regularly, vaginal commensal probiotics in ice-cream were effective in optimizing both the vaginal and intestinal microbiota in pregnant women at increased risk of pregnancy loss, particularly preterm birth. This emphasises the need for adequately powered trials to test whether early pregnancy vaginal microbiome modulation can improve clinical outcomes.