The Vaginal Microbiome in Pregnancy: Microbial Changes, Functions and Pregnancy Outcomes

Abstract

The vaginal microbiome undergoes dynamic changes during pregnancy and plays an important role in maintaining maternal reproductive health and supporting a healthy pregnancy. The vaginal microbial community is commonly dominated by Lactobacillus species, which contribute to vaginal homeostasis through lactic acid production, maintenance of a low vaginal pH, the inhibition of pathogenic microorganisms, and modulation of host immune responses. Pregnancy-associated hormonal and physiological changes can influence the composition, diversity, and functional activity of the vaginal microbiome. In many healthy pregnancies, increased dominance of Lactobacillus and reduced microbial diversity are observed, although substantial interindividual and population-level variations exist. Disruption of this microbial balance, commonly referred to as vaginal dysbiosis, has been associated with bacterial vaginosis, vulvovaginal infections, and adverse pregnancy outcomes. Alterations in the vaginal microbiome have been investigated in relation to preterm birth, premature rupture of membranes, spontaneous abortion, chorioamnionitis, and other pregnancy complications. Microbial metabolites, biofilm formation, inflammatory pathways, and interactions between vaginal microorganisms and the maternal immune system may contribute to these associations. Recent advances in culture-independent approaches, particularly 16S rRNA gene sequencing, shotgun metagenomics, and multi-omics analyses, have improved understanding of microbial composition and function during pregnancy. This mini-review summarizes current knowledge of the vaginal microbiome during pregnancy, focusing on pregnancy-associated microbial changes, major microbial functions, mechanisms underlying microbial–host interactions, and their potential relationships with pregnancy outcomes. Understanding these microbial dynamics may contribute to the development of microbiome-based biomarkers and targeted strategies for improving maternal and neonatal health.