Main findings
This is the largest cross-sectional study conducted based on 16S rRNA sequencing that explored differences in VMB composition between the PCOS and control groups. Compared with the control group, we observed increased diversity and intra-group variability of the VMB in PCOS, including a significant declination in the abundance ofLactobacillus and the enrichment of potential pathogens, including U . parvum , G. vaginalis , P. buccalis, P. timonensis, and A. baumanni . Additionally, serum levels of LH, T, and AMH were closely associated with U.parvum, A. baumannii, and P. buccalis . We also found that opportunistic pathogens, such as L. crispus, P. timonensis, and P. buccalis contributed to alter the vaginal microbiome in PCOS and was identified as key bacteria, which drive changes in the vaginal microbial interaction network in patients with PCOS.