Vaginal microbiome types show differing associations with pregnancy after assisted reproduction

A systematic review and network meta-analysis published in Human Reproduction Update evaluated associations between vaginal community state types (CSTs) and pregnancy after medically assisted reproduction, including IVF with or without ICSI and intrauterine insemination. The review included 12 longitudinal studies involving 2,289 women, with sequencing-based microbiome assessment before embryo transfer or insemination. Direct and indirect evidence was combined across six CST categories.

Compared with Lactobacillus crispatus-dominated communities, L. jensenii-dominated communities were associated with lower odds of pregnancy (OR 0.42, 95% CI 0.19–0.92), as were low-lactobacillus communities (OR 0.59, 95% CI 0.38–0.91). Other lactobacilli, including L. gasseri and L. iners, showed no statistically significant differences compared with L. crispatus. Tests found no evidence of overall or loop inconsistency in the primary network, although some subgroup networks showed local inconsistency.

These findings challenge the assumption that all Lactobacillus-dominated communities have similar associations with reproductive outcomes, but do not establish causation or justify clinical CST profiling. Interpretation is limited by observational designs, residual confounding, clinical and methodological heterogeneity, and sparse comparisons. Only five studies reported live births, totaling 57 events. Inconsistent reporting of potential effect modifiers prevented formal assessment of transitivity, a key network meta-analysis assumption. Larger standardized prospective studies are needed to assess prognostic usefulness and whether microbiome-targeted interventions improve outcomes.