Objective <p>To compare the angle of progression (AoP) and the progression distance (PD) during the early active phase, first stage of labor in term nulliparous women between successful vaginal delivery and cesarean section due to active phase arrest or prolonged second stage of labor groups.</p> Method <p>A prospective observational study was conducted between July 2019 and May 2020 at the labor room of Siriraj Hospital. Cervical dilatation was assessed by digital examination to ensure an early active phase of labor, and a transperineal ultrasound was performed to measure the angle of progression (AoP) and progression distance (PD). The delivery outcomes were divided into successful vaginal delivery (spontaneous or operative) and cesarean section due to active phase arrest or prolonged second stage of labor. Covariates were documented, including maternal age, maternal body mass index, total weight gain during pregnancy, gestational age, and fetal birth weight.</p> Results <p>A total of 149 term singleton nulliparous women with vertex presentation were consecutively enrolled. Six women who delivered by cesarean section due to non-reassuring fetal heart rate were excluded. Among 143 women who were eligible for further analysis, 108 (75.5%) pregnant women had successful vaginal delivery, while 35 (24.5%) women had cesarean section. The area under the curve indicated that AoP and PD were associated with a successful vaginal delivery (AUCs of 0.67 for AoP and 0.69 for PD). The optimal cut-off points using AoP were ≥ 90 ^° (sensitivity 85.2%, specificity 45.7%) and PD ≥ 0&#xa0;cm (sensitivity 86.1%, specificity 42.9%).</p> Conclusion <p>AoP and PD using standard 2-dimensional ultrasonography at the early active phase, first stage of labor, demonstrated a modest association with successful vaginal delivery. Further studies are warranted to explore the benefit of AoP and PD in clinical applications.</p>