Risk stratification of preterm birth using the uterocervical angle and its rate of change in mid- and late-pregnancy: a single-center retrospective study

PURPOSE: Mid-pregnancy cervical length (CL) has limited predictive performance for spontaneous preterm birth (sPTB) in the normal range. The uterocervical angle (UCA) is a promising marker, but evidence regarding late-pregnancy UCA and its longitudinal change is limited. We evaluated UCA in mid- and late-pregnancy and the % change (ΔUCA) as predictors of sPTB, and developed a pragmatic risk-stratification scheme using these parameters. METHODS: In a single-center retrospective study, 163 singleton pregnancies were analyzed. UCA was measured on transvaginal ultrasound at 16-24 weeks (mid-pregnancy) and 25-33 weeks (late-pregnancy). ΔUCA was calculated as the % change from mid to late-pregnancy. Predictive performance for sPTB (< 37 weeks) was assessed using logistic regression and receiver operating characteristic analysis. RESULTS: A mid-pregnancy UCA ≥ 105° had a sensitivity of 85.4%, specificity of 76.9%, and area under the curve (AUC) of 0.858 (95% CI 0.768-0.948) for prediction of sPTB. In contrast, CL < 25 mm had a sensitivity of 8.3% (mid-pregnancy) and 17.9% (late-pregnancy). A late-pregnancy UCA ≥ 112° had a sensitivity of 81.8%, specificity of 56.7%, and AUC of 0.728 (95% confidence interval [CI], 0.623-0.833), and ΔUCA ≥ + 12% predicted sPTB with a sensitivity of 81.2%, specificity of 66.7%, and AUC of 0.742 (95% CI 0.579-0.905). Using three criteria (mid-pregnancy UCA ≥ 105°, late-pregnancy UCA ≥ 112°, ΔUCA ≥ + 12%), preterm birth rates were 1.4% (low-risk: 0 points) vs. 46.2% (high-risk: 3 points) (p < 0.001). CONCLUSIONS: UCA in mid- and late-pregnancy and ΔUCA predict sPTB with higher sensitivity than CL shortening alone, offering a noninvasive complement to current screening. In particular, a mid-pregnancy UCA ≥ 105° and ΔUCA ≥ + 12% may identify clinically important high-risk cases.