Abstract

The vaginal microbiome is increasingly recognized as an important determinant of female reproductive health, with emerging evidence linking its composition and function to fertility, implantation, and pregnancy outcomes. This narrative review synthesizes current evidence on the role of the vaginal microbiome in natural conception and assisted reproductive technology (ART), with emphasis on underlying mechanisms, clinical implications, and emerging therapeutic applications. Contemporary literature examining vaginal microbiome composition, community state types (CSTs), host-microbiome interactions, and reproductive outcomes was qualitatively synthesized alongside evidence from mechanistic studies and emerging multi-omics and artificial intelligence (AI)-based approaches. Lactobacillus-dominant profiles, particularly those enriched in Lactobacillus crispatus, are often associated with more favorable reproductive outcomes, whereas Lactobacillus iners-dominant communities may show more variable associations; dysbiotic, highly diverse microbial profiles have been associated with adverse outcomes including infertility, implantation failure, and pregnancy loss, although these relationships vary according to the Lactobacillus species involved, sampling compartment, population studied, and reproductive endpoint. The vaginal microbiome may influence reproductive success through effects on epithelial barrier integrity, immune regulation, inflammatory signaling, microbial metabolite production, sperm function, and endometrial receptivity. Emerging evidence also supports functional interplay between the vaginal and endometrial microbial environments. In natural conception, microbial composition may affect sperm viability, fertilization, and early pregnancy maintenance, whereas in ART, it has been associated with implantation, clinical pregnancy, and live birth outcomes. Multi-omics and AI-based approaches may improve risk stratification and predictive modeling, while microbiome-directed interventions, including probiotics and vaginal microbiota transplantation, remain promising but investigational. The vaginal microbiome therefore represents a potential biomarker and investigational therapeutic target in reproductive medicine; however, routine clinical application remains limited by methodological heterogeneity, inconsistent definitions of dysbiosis, and insufficient interventional evidence. Standardized sampling and analytical methods, together with well-designed prospective and interventional studies, are needed before microbiome profiling and targeted modulation can be integrated into routine fertility care.