The reproductive tract microbiome and female fertility: dysbiosis, disease links, and emerging therapeutic strategies.

The reproductive tract microbiome plays a pivotal role in female fertility, with Lactobacillus-dominated communities maintaining a protective, low-pH environment. Dysbiosis-characterized by a reduction in Lactobacillus species and overgrowth of anaerobes-is associated with adverse outcomes. Chronic endometritis frequently involves diminished Lactobacillus species and colonization by pathogenic microbes such as Gardnerella and Escherichia, and antibiotic treatment may restore eubiosis and has been reported to improve implantation rates. Recurrent implantation failure is often linked to non-Lactobacillus-dominated endometrial microbiota, which can be partially normalized through combined antibiotic and probiotic interventions. In polycystic ovary syndrome, gut dysbiosis-marked by low microbial diversity, reduced short-chain fatty acid-producing bacteria, and increased lipopolysaccharide-producing Gram-negative species-correlates with both metabolic and reproductive dysfunction. Dietary fiber, probiotics, and metformin may help reestablish microbial balance. Patients with endometriosis and adenomyosis tend to harbor high-diversity reproductive tract microbiota with decreased Lactobacillus abundance, potentially exacerbating inflammatory pathways. During pregnancy, a Lactobacillus-rich vaginal microbiota is associated with lower risks of miscarriage and preterm birth, whereas bacterial vaginosis-like, high-diversity communities are linked to increased risks. Emerging therapies-including antibiotics, vaginal probiotics, and vaginal microbiota transplantation-aim to restore eubiosis and improve reproductive outcomes. Collectively, this review highlights the impact of dysbiosis on fertility and summarizes emerging therapeutic strategies to optimize reproductive success.