Vaginal microbiome composition in pregnant and non-pregnant women: community structure, population variation, clinical impact, and metagenomics approaches

The vaginal microbiome plays a critical role in reproductive health and undergoes characteristic remodeling during pregnancy that influences maternal and neonatal outcomes. Although the non-pregnant vaginal microbiome shows substantial inter-individual variability, pregnancy is associated with reduced microbial diversity and increased dominance by Lactobacillus species, creating a protective environment for fetal development. Disruption of this balance, termed vaginal dysbiosis, has been linked to adverse obstetric and neonatal outcomes. This narrative review synthesizes current evidence on pregnancy-associated vaginal microbiome dynamics, with emphasis on community state types (CSTs), gestational changes, population-specific variation, and clinical implications. We review studies that use 16S rRNA sequencing, next-generation sequencing, and shotgun metagenomics to characterize microbial composition across pregnancy and the postpartum period. Lactobacillus -dominated communities, particularly those dominated by Lactobacillus crispatus , are consistently associated with microbiome stability and favorable pregnancy outcomes, whereas high-diversity anaerobic communities (CST IV) are linked to bacterial vaginosis, preterm birth, miscarriage, gestational diabetes mellitus, and infection-related complications. The vaginal microbiome composition varies significantly across racial, ethnic, and geographic populations. African-descended populations more often show L. iners -dominant or diverse anaerobic profiles, whereas European populations more commonly show L. crispatus dominance. Future longitudinal and mechanistic studies across diverse populations are needed to establish causality and evaluate microbiome-based interventions to improve maternal and neonatal health.