A cross-sectional pilot study of birth mode and vaginal microbiota in reproductive-age women Original paper

What was studied?

This study examined the relationship between birth mode and vaginal microbiota in adulthood, evaluating whether being born by Cesarean section influences a woman’s likelihood of developing a low-Lactobacillus vaginal community state type (CST IV, also known as Molecular-BV). Using archived vaginal samples from two U.S. cohorts and newly collected survey data, the researchers assessed microbial composition via 16S rRNA gene sequencing and compared the prevalence of Lactobacillus-dominated versus dysbiotic CSTs. Birth mode and vaginal microbiota associations were analyzed with logistic regression, incorporating BMI as a key confounder.

Who was studied?

The study included 144 reproductive-age women originally enrolled in the HCL and VM400 studies. Participants were 17–44 years old, mostly nulliparous, and without active menstruation or recent antibiotic use at sampling. Twenty-seven women (19%) reported being born by C-section. Vaginal specimens were clinician- or self-collected depending on the parent study, and microbiota profiles were clustered into CSTs based on the relative abundance of Lactobacillus species versus BV-associated anaerobes. Marked demographic and behavioral differences existed between the two study cohorts, necessitating stratified analyses.

Most important findings

Across the combined cohort, C-section birth was associated with a non-significant trend toward higher odds of Molecular-BV (aOR 1.22). However, stratification revealed a stronger association in the HCL cohort, where C-section birth conferred approximately 3.5-fold higher odds of CST IV. The VM400 cohort showed no such association, likely due to differences in sample size and participant characteristics. Prevotella bivia emerged as the most discriminative taxon linked to C-section birth, with relative abundance ≥2.8% markedly increasing the probability that a woman was C-section–born. This species is a known marker of BV and a contributor to mucosal inflammation. Heatmap analyses visually confirmed greater prevalence of P. bivia and other BV-associated anaerobes in women with CST IV profiles, while Lactobacillus jensenii and L. iners trended higher among vaginally delivered women.

Key implications

The findings suggest that birth mode may exert a subtle yet persistent influence on vaginal microbial ecology into adulthood. C-section birth may predispose some women to a less protective vaginal environment characterized by reduced Lactobacillus dominance and greater abundance of BV-associated anaerobes such as P. bivia. Because Molecular-BV is linked to heightened risk of bacterial vaginosis, sexually transmitted infections, and adverse reproductive outcomes, early-life microbial exposures may represent a previously underappreciated determinant of long-term vaginal health. Larger longitudinal studies are needed to clarify causal pathways, incorporate maternal and early-childhood factors, and evaluate whether interventions such as microbial seeding or targeted probiotics could modify risk trajectories.

Citation

Stennett CA, Dyer TV, He X, Robinson CK, Ravel J, Ghanem KG, Brotman RM. A cross-sectional pilot study of birth mode and vaginal microbiota in reproductive-age women. PLoS One. 2020;15(4):e0228574. doi:10.1371/journal.pone.0228574