The role of the angle of progression in predicting spontaneous vaginal delivery in women with singleton pregnancies.

OBJECTIVE

This study aimed to evaluate the diagnostic accuracy of the angle of progression (AOP), measured by ultrasound at the onset of the second stage of labor, as a predictor of spontaneous vaginal delivery in term singleton pregnancies, and to identify a cutoff value for the AOP angle that could predict normal delivery in women with occiput anterior (OA) cephalic presentation.

METHODS

This prospective, observational study was carried out at a single tertiary center between February 2023 and January 2025. The study population consisted of patients at the beginning of the second stage of labor with a medical indication for vaginal delivery and enrolled after cervical preparation. Only full-term pregnancies with OA presentation were included. Transperineal ultrasound was used to measure the AOP during the second stage of labor. Sonographic findings from women who achieved spontaneous vaginal delivery were evaluated and subsequently compared with those of women who required cesarean section. Clinical data and delivery outcomes were retrieved from medical records.

RESULTS

A total of 162 patient applications were reviewed. Of these, 38 patients (23.46%) were not in active labor, and 28 patients (17.28%) underwent an emergency cesarean section (CS) before reaching active labor. Additionally, 17 patients (10.49%) had an operative vaginal delivery, while 79 patients (48.77%) had spontaneous vaginal delivery (SVD). Angle of progression was significantly different between the groups. The average AOP for CSs (118.00 ± 9.34) was narrower compared with SVDs (124.09 ± 7.58), with a statistically significant difference (P = 0.001). Logistic regression identified AOP as the most important predictor of delivery mode, with a 1° increase in AOP increasing the likelihood of SVD 0.9-fold (OR 0.916; P = 0.002). Receiver operating characteristic analysis showed that AOP had a moderate ability to predict SVD (area under the curve = 0.687; P = 0.003), with a cutoff value of AOP ≥123° offering 77.9% specificity and 89.5% sensitivity for predicting SVD in women.

CONCLUSION

The AOP measured by transperineal ultrasound at the beginning of the second stage of labor can predict SVD in term pregnancies and can be used in conjunction with physical examination and other clinical factors for the management of labor.