VAGINAL MICROBIOTA AND REPRODUCTIVE HEALTH: FERTILITY, PREGNANCY, AND VAGINAL MICROBIOTA TRANSPLANTATION

The vaginal microbiota is a dynamic ecosystem made up of many different types of bacteria that live on the vaginal epithelial surface and interact with each other. The predominance of Lactobacillus species maintains the vaginal pH within an acidic range, thereby inhibiting the growth of pathogenic microorganisms and helping regulate local immunological responses. Vaginal microbiota undergoes ongoing changes throughout life and is impacted by various factors, including hormonal status, age, sexual activity, hygiene practices, antibiotic exposure, dietary habits, psychological stress, and environmental conditions. These variables play a significant role in defining microbial composition and stability and are essential determinants in the development of vaginal dysbiosis. Vaginal dysbiosis, characterized by a disruption of the normal microbial balance, is becoming recognized as a significant biological component affecting both natural fertility and the outcomes of assisted reproductive technologies. The decline of Lactobacillus dominance, coupled with the proliferation of anaerobic and potentially pathogenic bacteria, may negatively impact sperm function, implantation, and early pregnancy via mechanisms including increased vaginal pH, chronic inflammation, and disruption of epithelial barrier integrity. Prior research has shown that infertile women display heightened microbial diversity, diminished levels of protective Lactobacillus species, and an elevated presence of anaerobic genera such as Gardnerella and Prevotella. However, despite accumulating evidence, a globally accepted diagnostic standard or conclusive microbiological biomarkers for vaginal dysbiosis have not yet been established, underlining the need for larger, methodologically harmonized investigations to create standardized diagnostic and therapeutic approaches. Pregnancy induces hormonal changes that result in a more stable and protective vaginal microbial profile, marked by diminished microbial diversity and heightened prevalence of Lactobacillus species, specifically Lactobacillus crispatus, Lactobacillus gasseri, and Lactobacillus jensenii. Dysbiotic profiles characterized by anaerobic bacteria, including Gardnerella, Prevotella, Sneathia, Atopobium, and Megasphaera have been linked to negative pregnancy outcomes, such as preterm birth, preterm premature rupture of membranes (PPROM), preeclampsia, and various obstetric complications. Microbiota-based therapeutic strategies, including probiotics, prebiotics, synbiotics, and vaginal microbiota transplantation, aim primarily to restore Lactobacillus dominance and reduce pathogenic microbial burden. Clinical studies indicate that vaginal probiotic interventions may enhance Lactobacillus abundance and diminish bacterial vaginosis associated taxa; nevertheless, the overall evidence is constrained by variability in probiotic strains, doses, and treatment durations. Vaginal microbiota transplantation has emerged as a viable alternative, especially for recurrent and treatment-resistant patients; nonetheless, its safety profile, long-term efficacy, and integration into standard clinical practice remain inadequately established.