Vaginal Ecosystem During Gestation and Puerperium: Microbiota, Dysbiosis, Infection and Fetal–Maternal Implications

Introduction: The vaginal ecosystem undergoes profound physiological adaptations during pregnancy and the puerperium through dynamic interactions among the vaginal microbiota, epithelial barrier, local immune system, and hormonal milieu. Disruption of this homeostasis may lead to vaginal dysbiosis and infection, with potential consequences for maternal, fetal, and neonatal health. Objective: This narrative review aimed to provide a comprehensive and updated overview of the vaginal ecosystem throughout pregnancy and the puerperium, integrating current evidence on physiological changes in the vaginal microbiota, mechanisms of dysbiosis, major vaginal infections, diagnostic approaches, therapeutic management, and maternal–fetal implications. Methods: A structured literature search was conducted in PubMed/MEDLINE and Scopus through July 2026. Priority was given to recent systematic reviews, meta-analyses, international clinical guidelines, randomized clinical trials, and observational studies addressing the vaginal microbiota, dysbiosis, bacterial vaginosis, vulvovaginal candidiasis, trichomoniasis, aerobic vaginitis, pregnancy, and the puerperium. Results: Pregnancy is generally characterized by a stable, low-diversity, Lactobacillus-dominated vaginal microbiota, whereas the postpartum period is associated with reduced Lactobacillus abundance, increased microbial diversity, and gradual restoration of eubiosis. Disruption of this ecosystem promotes biofilm formation, microbial persistence, inflammation, and ascending infection. Bacterial vaginosis, vulvovaginal candidiasis, trichomoniasis, and aerobic vaginitis represent the major vaginal infections during pregnancy and the puerperium and have varying associations with adverse outcomes, including preterm birth, preterm premature rupture of membranes, chorioamnionitis, postpartum infection, and neonatal morbidity. Molecular diagnostics and microbiome profiling have improved etiological characterization, while emerging microbiome-directed interventions offer potential strategies for restoring vaginal homeostasis. Conclusions: Current evidence supports an increasingly ecosystem-centered approach to vaginal health during pregnancy and the puerperium. Accurate etiological diagnosis and evidence-based treatment remain essential, while preservation and restoration of vaginal homeostasis may represent important complementary objectives for improving maternal, fetal, and neonatal outcomes.