Distribution of uterocervical angles of pregnant women at 16+0 to 23+6 weeks gestation with low risk for preterm delivery: First Vietnamese cohort of women with singleton pregnancies

Abstract

Abstract Background: Cervical length (CL) measured by ultrasound in the second trimester is a predictor of spontaneous preterm birth (sPTB). The uterocervical angle (UCA) has recently been investigated as a parameter to identify women at risk of sPTB. This study aimed to investigate the UCAs’ distribution in singleton pregnant women at 16+0-23+6 weeks of gestation with low risk for sPTB. Methods: This was a prospective cohort study of 1,051 pregnant women with singleton pregnancies at low risk for preterm delivery. Pregnant women with a viable singleton fetus at 16+0-23+6 weeks of gestation were enrolled in the study conducted at the Haiphong Hospital of Obstetrics and Gynecology, Vietnam, from 09/2019 to 09/2020. CL and the UCA were assessed using transvaginal ultrasonography (TVS) by a single sonographer. Subjects were followed-up until the end of pregnancy, and maternal and neonatal outcomes were recorded. The UCAs’ range and their relationship with gestational age were evaluated using regression analysis. P<0.05 was considered statistically significant. Results: The normal range of the UCA (5th-95th percentiles) was 46.47° (95% CI, 40.27°-51.81°) to 127.06° (95% CI, 123.02°-130.71°). The UCAs in the preterm birth (<37 weeks) and full-term groups were 117.86°±20.25° and 83.80°±24.18°, respectively (p<0.001). Linear regression analysis showed a significant change in the UCA range from 16+0 to 23+6 weeks of gestation (2.51 degrees per week, p<0.001). The quadratic function yielded the highest correlation coefficient in the variation rule of the UCA values (r2=0.051). A total of 42/63 (66.7%) patients with preterm birth <37 weeks had a UCA above the 75th percentile. The rate of UCA values ≥95° was significantly higher in the sPTB group than in full-term delivery group (88.9% vs. 31.3%, p<0.001). Conclusions: The UCA values in the preterm birth <37 weeks group were significantly wider in the full-term delivery group (p<0.001), and the majority of women with preterm birth had an UCA ≥ 95° compared with those with full-term delivery (p<0.001). It is advisable to monitor the UCA, especially in pregnant women with a UCA value ≥ 95° at 16+0-23+6 weeks of gestation.