Non-Lactobacillus dominance of the vagina is associated with reduced live birth rate following IVF/ICSI: a propensity score-matched cohort study

Purpose Whether the dominant status of vaginal Lactobacillus is associated with IVF/ICSI outcomes. Methods This is a propensity score-matched retrospective cohort study consists of 2285 women undergoing their first fresh autologous IVF cycles. We divided the patients into the Lactobacillus-dominant group and non-Lactobacillus-dominant group based on the abundance of Lactobacillus in Gram-stained vaginal smear examined by microscopy. We compared IVF outcomes between the two groups. We matched Lactobacillus-dominant women with non-Lactobacillus-dominant women by propensity score (PS) to reduce the impact of confounding factors. We evaluated the effect of vaginal Lactobacillus on live birth using univariate and multivariate analysis models. We also conducted interaction and stratified analyses. Results Compare to the Lactobacillus-dominant group, the biochemical pregnancy rate (50.12% vs. 57.61%, P = 0.03), clinical pregnancy rate (40.98% vs. 50.82%, P < 0.01), and live birth rate (31.83% vs. 41.22%, P < 0.01) were significantly lower in the non-Lactobacillus-dominant group, the preclinical pregnancy loss rate (18.22% vs. 11.79%, P = 0.05) and preterm birth rate (33.09% vs. 21.59%, P = 0.02) were significantly higher in the non-Lactobacillus-dominant group. However, the miscarriage rate (18.86% vs. 15.67%, P = 0.40) and ectopic pregnancy rate (1.41% vs.1.64%, P = 0.78) were similar between the two groups. Loss dominance of Lactobacillus in the vagina was an independent risk factor for live birth (OR 0.66, 95% CI 0.50-0.88). Conclusions Loss dominance of Lactobacillus in the vagina negatively affects IVF outcomes by decreasing the chances of pregnancy and live birth, increasing risks of preclinical pregnancy loss and preterm birth.