Uterocervical angle as a predictor for spontaneous singleton preterm birth: a prospective observational study

The use of cervical length (CL) to predict spontaneous preterm birth (sPTB) is limited in performance due to the low prevalence of a short cervix in the Thai population. Therefore, this study aims to evaluate the diagnostic performance of the uterocervical angle (UCA) in comparison with CL, and the integration of these parameters alongside cervical wedging to predict sPTB.

This prospective cohort study was designed to assess the diagnostic performance of UCA, CL, and cervical wedging for sPTB in singleton pregnancies, between gestational ages of 16 and 24 weeks, using transvaginal ultrasonography. The primary outcome was the diagnostic performance of the UCA, along with the integration of UCA with other parameters in women who delivered before 37 and 34 weeks.

A total of 261 participants were included in the analysis. The optimal cut-off value for predicting sPTB before 37 weeks was 85 degrees for UCA, with a sensitivity of 44.8%, specificity of 46.6%, and a diagnostic odds ratio (DOR) of 0.71. For predicting sPTB before 34 weeks, the optimal cut-off for UCA was found to be 95 degrees, with a sensitivity of 71.4%, specificity of 59.8%, and a DOR of 3.73. The integration of UCA with CL or cervical wedging did not yield superior results compared to CL alone. The area under the receiver operating characteristic curve showed that UCA over 85 degrees was not as effective as CL under 33 mm for predicting sPTB before 37 weeks (0.54 vs. 0.51, respectively). However, CL under 30 mm was better than UCA over 95 degrees at predicting sPTB before 34 weeks (0.71 vs. 0.66, respectively).

A wider UCA is associated with an increased risk of sPTB. However, while UCA alone does not have as high diagnostic performance as CL or cervical wedging alone in predicting sPTB.