Cervical Length and Uterocervical Angle for Optimal Timing in Predicting Preterm Birth among Twin Pregnancies: A Longitudinal Study

Background: Twin pregnancies carry a significantly higher risk of preterm birth; however, measuring cervical length with sonography during the mid-trimester provided limited predictive accuracy when used as a standalone test. This study aimed to investigate the relationship between cervical length (CL) and uterocervical angle (UCA) for predicting preterm birth in twins, and to determinethe gestational age at which the combined CL-UCA measurement offers the best predictive ability. Methods: A prospective longitudinal cohort study involving 93 twin pregnancies at 14 weeks of gestation was conducted at Haiphong Medical University Hospital, from 09/2023 to 08/2025. Each patient underwent a transvaginal ultrasound to measure CL and UCA every 2 weeks from 14 to 24 weeks, performed by a certified sonographer. Blood samples for interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) testing were collected at 16 weeks. Patients were followed until delivery to determine pregnancy outcomes, including spontaneous preterm birth (PTB) before 37 weeks and before 34 weeks of gestation. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to evaluate the association between CL-UCA and PTB. A multivariate binary regression model was used to analyze the relationship between CL-UCA and PTB, with p-values <0.05 considered significant. Receiver operating characteristic (ROC) curves assessed the ability of CL-UCA to predict PTB. Results: At 22 weeks of gestation, significant associations were found between both CL and UCA with PTB <34 weeks, with ORs (95% CI) of 0.797 (0.647-0.982) and 1.086 (1.000-1.179), respectively, as well as with PTB <37 weeks, with ORs (95% CI) of 0.906 (0.822-1.000) and 1.038 (1.007-1.070). Combined CL and UCA showed good predictive value for PTB <34 weeks, with an AUC of 0.886 (95% CI: 0.809-0.963) at 22 weeks of gestation, and also demonstrated good predictive value for PTB <37 weeks, with an AUC of 0.825 (95% CI: 0.743-0.907) at 24 weeks of gestation. Inflammatory markers at 16 weeks were not associated with PTB (p >0.05). Conclusions: The study's findings show that the 22-week assessment has the highest predictive ability for combined CL and UCA screening for PTB, making it the best timing for mid-trimester screening in twin pregnancies.