Adverse effect of lactobacilli‐depauperate cervicovaginal microbiota on pregnancy outcomes in women undergoing frozen–thawed embryo transfer

PURPOSE: The cervicovaginal microbiota is essential for maintaining the health of the female reproductive tract. However, whether cervicovaginal microbiota status prior to frozen embryo transfer (FET) associates with pregnancy outcomes is largely unexplored. METHODS: Cervical mucus from 29 women who had undergone FET was collected. Microbial composition was analyzed using 16 S rRNA gene sequence to assess the correlation to the pregnancy outcomes. RESULTS: CST‐categorized Lactobacillus was the most dominant (41.71%) in the pregnant group, while CST‐IV‐based and BV‐related Gardnerella (34.96%) prevailed in the non‐pregnant group. The average abundance of Gardnerella compared non‐pregnant to pregnant women was the highest (34.96% vs. 4.22%, p = 0.0015) among other CST‐IV indicator bacteria. Multivariate analysis revealed that CST‐IV‐related bacteria have a significantly adverse effect on ongoing pregnancy outcomes (odds ratio, 0.083; 95% confidence index, 0.012–0.589, p = 0.013*). CONCLUSIONS: The study found that the CST‐IV microbiota, with significantly increasing Gardnerella and the loss of Lactobacilli as the dominant bacteria, can potentially contribute to pregnancy failure. Therefore, dysbiotic microbiota may be a risk factor in women undergoing FET. Assessing the health of the cervicovaginal microbiota prior to FET would enable couples to make a more thoughtful decision on the timing and might improve pregnancy outcomes.