Uterocervical angle measurement for preterm birth prediction in singleton pregnant women with no history of preterm birth and normal cervical length: A prospective cohort study.

Objective: To evaluate the ability of second trimester uterocervical angle (UCA) to predict spontaneous preterm birth (sPTB) in low-risk singleton pregnant women.

Study Design: Transvaginal sonographies were performed in the second trimester of 450 singleton pregnant women with no history of sPTB and no history of second trimester miscarriage with normal cervical length (CL) who attended antenatal care at Songklanagarind Hospital, a tertiary teaching hospital in southern Thailand. Gestational ages at delivery were recorded then the UCA values were evaluated according to sPTB occurrence. The differences in mean values of UCA between sPTB and full-term groups were evaluated using t-test. A receiver operating characteristics (ROC) curve was used to assess the ability of UCA to predict sPTB.

Results: After excluding women with unknown pregnancy outcomes or missing UCA images, the sPTB rate was 34/421 (8.1 %). In women with anteflexed uterus, the mean UCA value was wider in the sPTB group compared to those with term birth if the measurements were performed at GA 19.5-24 weeks (sPTB group, 123.4°vs controls, 104.3°; P = 0.017). The ROC curve showed an area under the curve (AUC) of 0.7045. The optimal UCA cut-off value was ≥110 degrees, which gave a sensitivity of 83.3 % and a specificity of 61.2 %. The positive predictive value (PPV) was 16.7 %, negative predictive value (NPV) 97.5 %, positive likelihood ratio (LR+) 2.2 and negative likelihood ratio (LR-) 0.3.

Conclusion: The UCA in the second trimester is not a good predictor of sPTB in low risk pregnant women.