ABSTRACT
OBJECTIVE: To investigate the predictive value of cervical length（CL）changes in spontaneous preterm birth（SPTB）in twin pregnancies in the second and third trimesters of pregnancy.METHODS: A retrospective analysis was made of 166 cases of twin pregnant women who underwent transvaginal ultrasound to measure CL during the second trimester of pregnancy（20~25 weeks）and the third trimester of pregnancy（28~32 weeks）from January 2014 to December 2017 in the Third Hospital of Peking University and Tongzhou Maternal and Child Health Hospital of Beijing.Evaluate the predictive value of CL changes in SPTB before 32 and 34 weeks.The area under the receiver-operating characteristics（ROC）curve was compared by bootstrap method.Assessment of the value of CL in the third trimester of pregnancy and CL in the second trimester of pregnancy alone in predicting SPTB before 32 and 34 weeks.RESULTS: Of the 166 cases,90 were full-term delivery and 76 were premature delivery.The median CL of mid and late pregnancy was 34 mm and 29 mm respectively,and it was 35.5 mm and 31 mm,and in full-term delivery.32.5 mm and21 mm in premature delivery,respectively.There were significant differences among the three groups（All P25 mm and CL shortening≥ 20%,it can better predict preterm birth before 32 weeks.