Abstract

Background: The human endometrium carries a unique low-biomass microbiome that has the potential to mediate the implantation of an embryo and support an outcome during Assisted Reproductive Technology (ART) yet available evidence is contradictory. Methods: The systematic review complied with PRISMA 2020. The 16S rRNA sequencing, shotgun metagenomics, or culturomics to characterize endometrial or other related genital tract microbiota was searched in PubMed, Embase, Web of Science and Scopus in original human studies. The risk of bias was determined with ROBINS-I, and (where possible) random-effects meta-on several data were similar) was used. Findings: Eleven studies were included on women who were undergoing ART. Eight studies were included in the meta-analysis that revealed that a Lactobacillus-dominated endometrial microbiome correlated with a much better implantation, clinical pregnancy, or live birth (OR 2.42, 95% CI 1.683.49; I2 = 54%). Reduced Lactobacillus dominance and microbial diversity were regular in chronic endometritis and adenomyosis. At the species level, data indicated that Lactobacillus crispatus was a more predictive indicator of successful live birth compared to total Lactobacillus abundance. Conclusion: The optimal ART results are found when a Lactobacillus-dominant endometrial microbiome is present, but standardized sampling, sequencing, and outcome measures are necessary before it can be put into routine clinical practice. Microbiome biomarkers ought to be validated by future multicenter, prospective studies. 

Keywords: Endometrial microbiome, Lactobacillus, Implantation, Embryo transfer, 16S Rrna sequencing, Chronic endometritis