Maternal Metabolic Status and Vaginal Microbiome Ecology in Early Pregnancy: Associations with Microbial Stability and Birth Outcomes

The aim of this study was to characterize the vaginal microbiome during early pregnancy according to maternal metabolic status, including prepregnancy body mass index (BMI) and gestational weight gain (GWG), and to explore its relationship with subsequent birth outcomes. A prospective observational cohort study was conducted with sixty-nine pregnant women recruited during the first trimester of pregnancy. Vaginal samples collected between 11 and 13.6 weeks of gestation were analyzed using long-read 16S-rRNA gene sequencing (Oxford Nanopore Technologies). Microbial composition, alpha diversity (richness, Shannon diversity, and evenness), and community structure were evaluated according to prepregnancy BMI, GWG, and birth outcomes. Vaginal microbial communities were predominantly composed of Lactobacillus species across all groups; however, distinct ecological configurations were observed according to maternal metabolic status. Women with normal prepregnancy BMI exhibited a greater representation of Lactobacillus crispatus, whereas overweight, obesity, and excessive GWG were characterized by a predominance of Lactobacillus iners. Maternal obesity was associated with reduced richness and diversity, a trend toward lower community evenness, and enrichment of anaerobic taxa. Women with adverse birth outcomes, particularly preterm birth, exhibited greater community heterogeneity and a higher contribution of non-Lactobacillus anaerobes. Overall, maternal metabolic status was associated with distinct vaginal microbiome configurations during early pregnancy. These findings suggest subtle ecological differences in the predominance of Lactobacillus species, community composition, and microbial diversity that may be relevant to subsequent obstetric outcomes.