Your vaginal and uterine microbiome

The reproductive tract is not sterile, and which bacteria dominate matters. A meta-analysis of 17 studies found vaginal dysbiosis associated with poorer IVF outcomes, with Lactobacillus crispatus dominance specifically — not Lactobacillus generally — linked to higher implantation and live birth rates.

Chronic endometritis is the uterine version: across 22 studies and 4,022 women it was characterized by reduced Lactobacillus and enrichment of Enterobacteriaceae, Ureaplasma and Proteobacteria. It is linked to recurrent implantation failure, recurrent loss and unexplained infertility, and it is treatable.

The probiotic question, answered honestly. Oral L. acidophilus and L. rhamnosus did not colonize the vagina above detection limits in a randomized trial — so most oral products marketed for vaginal health are unlikely to reach their target. Vaginal capsules of L. gasseri/rhamnosus before fertility treatment performed no better than placebo. But LACTIN-V (L. crispatus CTV-05), applied vaginally after metronidazole, achieved 79–84% colonization versus 2–6% on placebo and significantly reduced recurrence (Cohen, NEJM 2020). Strain and route both matter.