The endometrial microbiota of women with or without a live birth within 12 months after a first failed IVF/ICSI cycle

Objective: To compare endometrial microbiota profiles of women with and without a live birth within 12 months after a failed first IVF/ICSI cycle, and by infertility cause and type. Design: Exploratory study. Setting: Secondary/tertiary care hospitals in the Netherlands. Population or sample: 141 infertile women with a failed first IVF/ICSI cycle. Endometrial tissue obtained during scratching by Pipelle in the natural cycle prior to the second IVF/ICSI cycle. Methods: Total DNA was extracted followed by 16S rRNA sequencing (V1-V2). Samples with <100 bacterial reads were excluded. Main outcome measures: Endometrial microbiota characteristics (alpha and beta diversities, relative abundances (RAs) of bacterial taxa and Lactobacillus-domination). Results: Lactobacillus was the most abundant genus in the majority of samples. The endometrial microbiota of women with a live birth compared to those without had a higher median Lactobacillus crispatus RA in targeted Wilcoxon analyses but not in untargeted ANCOM-BC analyses. Taxa were not differentially relatively abundant by infertility cause. Women with primary compared to secondary infertility had a higher median L. crispatus and “other bacteria” RAs, and a lower median Gardnerella vaginalis RA in targeted Wilcoxon analyses; mean G. vaginalis RA was also lower in untargeted ANCOM-BC analyses. No other microbiota outcomes differed between groups. Conclusions: Our data add to the evidence for a beneficial role of L. crispatus in IVF/ICSI success and suggest that secondary infertility may be associated with endometrial dysbiosis more often than primary infertility.