The Use of Mid-Pregnancy Cervical Length to Predict Preterm Birth in Brazilian Asymptomatic Twin Gestations

Abstract Objective To describe a reference curve for cervical length (CL) in mid-trimester twin gestations using transvaginal ultrasound (TVU) and to investigate whether short CL increases spontaneous preterm birth (sPTB) in asymptomatic twin pregnancies. Methods This was a prospective cohort study performed at 17 outpatient antenatal facilities of Brazil with women at 18 0/7 to 22 6/7 weeks of gestation who participated in a randomized clinical trial screening phase (P5 trial) between July 2015 and March 2019. TVU was performed to provide CL measurement in all screened women. Almost all women with CL ≤ 30 mm received vaginal progesterone 200mg/day and they were also randomized to receive cervical pessary or not. We considered data from the CL distribution among asymptomatic twin pregnancies and analyzed CL and its association with PTB generating receiver operating characteristics (ROC) curves and Kaplan-Meier curves. Results A total of 253 pregnant women with twins were included in the distribution curve. The mean CL was 33.7 mm and median was 35.5mm. The 10th percentile was 17.8mm. We identified a PTB rate of 73.9% (187/253) with 33.6% of sPTB < 37 (85/253) and 15% (38/253) of sPTB < 34 weeks. The best cutoff point to predict sPTB < 37 was 24.15 mm. However, the ROC curve showed a poor performance (0.64). The Kaplan-Meier survival curves identified that only CL values ≤ 20mm were associated to sPTB < 34 weeks. Conclusion A cutoff point of CL ≤ 20 mm can be interesting point to identify short cervix in Brazilian twin pregnancies. However, in Brazilian asymptomatic twin pregnancies, CL does not show a good performance to predict PTB.

摘要 目的 本研究旨在借助经阴道超声（transvaginal ultrasound, TVU）构建中期妊娠双胎孕妇的宫颈长度（cervical length, CL）参考曲线，并探讨无症状双胎妊娠中宫颈长度偏短是否会升高自发性早产（spontaneous preterm birth, sPTB）的发生风险。方法 本研究为前瞻性队列研究，纳入2015年7月至2019年3月间，在巴西17家产前门诊机构参与随机临床试验筛查阶段（P5试验）、孕周为18⁰/₇~22⁶/₇周的孕妇。所有入组筛查的孕妇均接受经阴道超声宫颈长度测量。对于宫颈长度≤30mm的孕妇，几乎全部予以每日200mg阴道用黄体酮治疗，并进一步随机分配至宫颈托干预组或对照组。本研究提取无症状双胎妊娠的宫颈长度分布数据，分析宫颈长度与早产（preterm birth, PTB）的相关性，构建受试者工作特征（receiver operating characteristics, ROC）曲线及Kaplan-Meier曲线。结果 本研究共纳入253例双胎妊娠孕妇用于构建宫颈长度分布曲线。研究对象的宫颈长度平均值为33.7mm，中位数为35.5mm，第10百分位数为17.8mm。本队列总体早产率为73.9%（187/253），其中孕37周前自发性早产发生率为33.6%（85/253），孕34周前自发性早产发生率为15%（38/253）。预测孕37周前自发性早产的最佳截断值为24.15mm，但受试者工作特征曲线显示该截断值的预测效能一般（曲线下面积0.64）。Kaplan-Meier生存曲线分析显示，仅宫颈长度≤20mm与孕34周前自发性早产存在相关性。结论 宫颈长度≤20mm可作为巴西双胎妊娠孕妇宫颈偏短的识别截断值，但在巴西无症状双胎妊娠人群中，宫颈长度对早产的预测效能并不理想。