Background Recent data suggests that birth mode (Cesarean section [C-section] versus vaginal delivery) is an important seeding event in the initial colonization of the human microbiome and is associated with long-term health. We sought to determine the association between C-section delivery and vaginal microbiota in adulthood.

Methods We re-contacted 144 adult women from two concluded studies. In a phone survey, women reported their birth mode, obesity, breastfeeding, and age at menarche. Vaginal microbiota was characterized on a single baseline sample by amplicon sequencing of the V3-V4 hypervariable regions of the 16S rRNA gene and clustered into community state types (CSTs). We evaluated the association between birth mode and low versus high relative abundance of Lactobacillus spp. in logistic regression models controlling for body mass index, a significant confounder in this study.

Results 19% (n=27) reported C-section delivery. Overall, C-section was non-significantly associated with increased odds of a low-Lactobacillus CST (aOR=1.22, 95% CI: 0.45, 3.32). Because the two archived studies had different participant characteristics and inclusion criteria (interaction p=0.048), we stratified the analysis by study site. In the study with larger sample size (n=88), women born via C-section had 3-fold higher odds of having low-Lactobacillus vaginal communities compared to vaginally-delivered women (aOR=3.55, p=0.06, 95% CI: 0.97, 13.02). No association was found in the smaller study (n=56, aOR=0.19, p=0.14, 95% CI: 0.02, 1.71).

Conclusion This cross-sectional study suggests a possible association between C-section and increased odds of a low-Lactobacillus vaginal microbiota in adulthood. However, this analysis is limited by relatively small sample size and lack of comparability in participant age, personal hygiene behaviors, and other characteristics between the study sites. Future longitudinal studies could better account for expected fluctuations in CST and may also explore confounders including behavioral factors and socioeconomic status known to be associated with both delivery mode and vaginal microbiota.

Disclosure No significant relationships.