Temporal shifts and cross-site relationships of oral, gut, and vaginal microbiota during the third trimester of pregnancy

Background

The maternal microbiome during pregnancy influences maternal and neonatal health, yet its dynamics and cross-site relationships in the third trimester remain unclear.

Methods

Oral, fecal, and vaginal samples were collected from 22 healthy pregnant women and analyzed using 16S rRNA gene sequencing.

Results

As pregnancy progressed, gut microbial richness significantly increased, while vaginal richness significantly declined. Source tracking showed that the majority of microbes originated from their respective niches, although low-level cross-site contributions were also observed. Correlation-based network analysis revealed complex associations among microbial communities across sites. The oral microbiome exhibited distinct relative contributions and network relationships to the gut and vaginal microbiomes. Moreover, some low-abundance genera (relative abundance <1 %) played a critical role in maintaining ecological balance compared to high-abundance genera.

Conclusions

This study demonstrates dynamic, site-specific microbial changes and highlights potential microbial connections across body sites during late pregnancy, offering new ecological insights relevant to maternal–fetal health.