Prediction of mode of delivery in nulliparous women by single measurement of angle of progression in active phase of first stage of labor

BACKGROUND: Intrapartum Ultrasonography (USG) has recently evolved as an objective method to assess the progress of labor. Many parameters, such as angle of progression (AOP), head perineal distance (HPD), midline angle, and head direction, are assessed to predict vaginal delivery. These parameters are measured transperineally and based on clinical experience. This route is unpleasant to the patient, similar to digital vaginal examination. This study assesses whether a single measurement of AOP when measured abdominally can predict vaginal delivery. METHODS: A total of 110 nulliparous women were recruited after ethical clearance and informed consent had been attained. AOP was measured in the active phase of labor (4-6 cm) by abdominal technique, and HPD and cervical dilatation were also measured using the translabial technique. The receiver operating characteristics curve was plotted for the AOP of all women, and the cut-off value to predict vaginal delivery was determined. RESULTS: Vaginal delivery occurred in 72.7% of women, and the cesarean section rate was 27.3%. The cut-off value of AOP was 99.5° (area under the curve = 0.683; P = 0.002), which predicted vaginal birth. When the AOP was 90°, 50% delivered vaginally, and when it was >120°, all could deliver vaginally. Maximum vaginal deliveries occurred at an HPD of ≤4 cm. Cesarean birth was needed for 10.9% with non-progress of labor. CONCLUSION: The AOP as measured by abdominal technique in the active phase of the first stage of labor had moderate sensitivity in predicting vaginal delivery and, hence, it is a useful screening tool.