Objective: To investigate the predictive value of cervical length (CL) measured by transvaginal ultrasound for preterm birth <32 weeks, <34 weeks in twin pregnancies in the second and the third trimester of pregnancy. Methods: A total of 490 twin pregnant women with CL measured by transvaginal ultrasound during the second trimester of pregnancy (20-24 weeks) and the third trimester of pregnancy (28-32 weeks) delivered in Peking University Third Hospital, and Tongzhou Maternal and Child Health Hospital from January 2014 to December 2017 were collected, and 161 cases out of which were measured by CL during both the second trimester and the third trimester of pregnancy. Based on the measured gestational weeks, 427 cases were in the second trimester group and 224 cases in the third trimester group. The predictive value of CL for preterm birth was evaluated by calculating the optimal cut-off point with sensitivity and specificity. Logistic regression analysis was used to assess the relationship between CL and preterm birth after adjusting for confounding factors (age of pregnant women, chorionic status, mulipara, assisted reproductive pregnancy and pre-pregnancy body mass index). Results: (1) The median CL of pregnant women in the second trimester group and the third trimester group were 36 mm (33-40 mm) and 28 mm (18-33 mm) respectively. In the second trimester group, 151 cases (35.4%, 151/427) were preterm birth and 276 cases (64.6%, 276/427) were full-term birth; the median CL of preterm and full-term pregnant women were 34 mm (30-37 mm) and 37 mm (34-40 mm), respectively, with significant difference (P<0.01). In the third trimester group, 100 cases (44.6%, 100/224) were preterm birth and 124 cases (55.4%, 124/224) were full-term birth; the median CL of preterm and full-term pregnant women were 22 mm (15-30 mm) and 31 mm (23-34 mm), respectively, with significant difference (P<0.01). (2) Prediction of preterm birth <32 weeks and <34 weeks was performed with CL in the second trimester group. The area under the receiver-operating characteristics curve were 0.78 (95%CI: 0.70-0.86) and 0.71 (95%CI: 0.64-0.79), respectively. The optimal cut-off points were 36.5 mm and 33.5 mm, respectively. After adjusting for confounding factors, CL was inversely associated with preterm birth <32 weeks and <34 weeks of gestation. (3) Prediction of preterm birth <32 weeks and <34 weeks were performed with CL in the third trimester group. The area under the receiver-operating characteristics curve were 0.86 (0.75-0.96) and 0.75 (0.67-0.84), respectively. The optimal cut-off points were 17.5 mm and 18.5 mm, respectively. After adjusting for confounding factors, CL was inversely associated with preterm birth at <32 weeks and <34 weeks of gestation. Conclusions: CL measured by transvaginal ultrasound in the second and the third trimester is a good predictor for preterm birth of twin pregnancy. CL≤36.5 mm and ≤33.5 mm at 20-24 weeks of gestation could predict preterm birth <32 weeks and <34 weeks respectively. CL≤17.5 mm and ≤18.5 mm at 28-32 weeks of gestation could predict preterm birth <32 weeks and <34 weeks respectively.
目的： 探讨双胎孕妇妊娠中期和晚期的子宫颈长度（CL）对妊娠<32周、<34周早产的预测价值。 方法： 收集2014年1月至2017年12月于北京大学第三医院和北京市通州区妇幼保健院分娩的妊娠中期（20~24周）和妊娠晚期（28~32周）行经阴道超声测量CL的双胎孕妇共490例，其中161例于妊娠中期及晚期均行CL测量。按照测量的孕周分为妊娠中期组427例，妊娠晚期组224例，评估CL对早产的预测价值，并以敏感度和特异度计算最佳界值。采用logistic回归分析，校正混杂因素后（孕妇年龄、绒毛膜性、经产妇、辅助生殖治疗、孕前体质指数），评估孕妇CL与早产之间的相关性。 结果： （1）妊娠中期组、妊娠晚期组孕妇的中位CL分别为36 mm（33~40 mm）、28 mm（18~33 mm）。妊娠中期组孕妇中，早产者151例（35.4%，151/427），足月分娩者276例（64.6%，276/427）；早产和足月分娩孕妇的中位CL分别为34 mm（30~37 mm）和37 mm（34~40 mm），两者比较，差异有统计学意义（P<0.01）。妊娠晚期组孕妇中，早产者100例（44.6%，100/224），足月分娩者124例（55.4%，124/224）；早产和足月分娩孕妇的中位CL分别为22 mm（15~30 mm）和31 mm（23~34 mm），两者比较，差异有统计学意义（P<0.01）。（2）采用妊娠中期CL预测妊娠<32周、<34周早产的受试者工作特征曲线下面积（AUC）分别为0.78（95%CI为0.70~0.86）、0.71（95%CI为0.64~0.79），其最佳界值分别为36.5、33.5 mm。校正混杂因素后，妊娠中期CL与妊娠<32周、<34周早产均呈负相关。（3）采用妊娠晚期CL预测妊娠<32周、<34周早产的AUC分别为0.86（95%CI为0.75~0.96）、0.75（95%CI为0.67~0.84），其最佳界值分别为17.5、18.5 mm。校正混杂因素后，妊娠晚期CL与妊娠<32周、<34周早产均呈负相关。 结论： 妊娠中期和晚期经阴道超声测量CL是无症状双胎孕妇早产的良好预测指标。妊娠20~24周CL≤36.5 mm和≤33.5 mm，可分别预测双胎妊娠<32周和<34周的早产；妊娠28~32周CL≤17.5 mm和≤18.5 mm，也可分别预测妊娠<32周和<34周的早产。.
Keywords: Cervical length measuement; Forecasting; Pregnancy, twins; Preterm birth; Ultrasound, prenatal.