Objective:To explore the predictive value of changes in vaginal microecology during pregnancy on adverse pregnancy outcomes in pregnant women with threatened preterm labor.Methods:The clinical data of 208 women with threatened preterm labor were retrospectively analyzed.According to the pregnancy outcomes,the pregnant women were divided into preterm group(n=75)and full-term group(n=133).The pH value of vaginal secretion,relative abundance of microbial flora and related biochemical indicators[hydrogen peroxide concentration(H2 O2),sialidase activity(SNA)and leukocyte esterase(LE)]were detected and compared be-tween the two groups.Receiver operating characteristic(ROC)curve were used to analyze the predictive value of vaginal microecologi-cal flora and related biochemical indicators on adverse pregnancy outcomes.Results:Compared with full-term group,the relative abun-dance of Lactobacillus in preterm group was lower(P＜0.05)while the pH value,relative abundances of Genus Gardnerella and posi-tive rates of H2O2 and LE were higher(P＜0.05).ROC curve analysis showed that the area under the curve(AUC)for predicting ad-verse pregnancy outcomes for pH value,Lactobacilli,and Genus Gardnerella was 0.712,0.931,and 0.921,with cutoff values of 4.14,59.95％,and 17.7％,respectively.Conclusion:The adverse pregnancy outcomes of pregnant women with threatened preterm labor are closely related to the changes of vaginal microecology.The relative abundance of Lactobacillus is lower than 59.95％,relative abun-dances of Genus Gardnerella is higher than 17.7％,pH value is higher than 4.14,suggesting that pregnant women have the risk of ad-verse pregnancy outcomes of threatened preterm labor.