Objective: To investigate dysbiosis of the vaginal microbiota related to increased risk of preterm premature rupture of fetal membrane (PPROM) and chorioamnionitis in singleton gestations with ultrasound-indicated cerclage. Design: Retrospective observational study. Setting: Fujian Maternity and Child Health Hospital. Population: 44 singleton gestations with ultrasound-indicated cerclage, including 13 cases of PPROM and 31 cases of normal-term delivery. Methods: Composition of the vaginal microbiota was assessed prior to cervical cerclage at 18–24 weeks of gestation, using MiSeq-based 16S rRNA gene sequencing. Main Outcome Measures: To characterize the vaginal microbial profile of women who later experienced PPROM and chorioamnionitis. Results: Furthermore, the vaginal microbiota of women who later experienced PPROM was relatively enriched with Streptococcus anginosus and Prevotella timonensis (P=0.042, P=0.032, respectively), while that of women who later experienced normal-term delivery was relatively enriched with Lactobacillus. Further, enrichment for Prevotella was noted in patients diagnosed with chorioamnionitis in the PPROM group (6 of 13, 53.8%), which was absent in women with normal histology in the PPROM group (P=0.012). Conclusions: Together, these results indicate that dysbiosis of the vaginal microbiota is a risk element for subsequent PPROM and chorioamnionitis in singleton gestations with ultrasound-indicated cerclage. These findings may contribute to the development of methods to identify pregnancies at high risk for cerclage failure following PPROM. Funding: This work was supported by a grant from the Fujian Maternity and Child Health Hospital Innovation Project (YCXZ 18-21). Keywords: Vaginal microbiota, PPROM, chorioamnionitis, ultrasound-indicated cerclage, Prevotella.