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

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 200 mg/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 35.5 mm. The 10th percentile was 17.8 mm. 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 <= 20 mm were associated to sPTB < 34 weeks. Conclusion A cutoff point of CL <= 20mm 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.

Automated summary

This study aimed to describe a reference curve for cervical length (CL) in mid-trimester twin gestations using transvaginal ultrasound (TVU), and investigate whether short CL increases the risk of spontaneous preterm birth (sPTB) in asymptomatic twin pregnancies. The results showed that CL does not perform well in predicting preterm birth in Brazilian asymptomatic twin pregnancies. However, a cutoff point of CL ≤ 20mm may be an interesting indicator to identify short cervix in Brazilian twin pregnancies.