Comparison of clinical findings and ultrasound parameters by the mode of delivery
The maternal and neonatal demographic characteristics compared between the vaginal delivery and cesarean delivery groups are shown in Table S1. There were no significant differences between these two groups, except for maternal height (161.2 ± 4.6 vs. 158.8±5.1 cm, P < 0.001) and neonatal birth weight (3390.5 ± 366.7 vs. 3550.7 ± 380.4 g, P < 0.001) (Table S1). Focusing on the sonographic parameters, the women who underwent vaginal delivery had a significantly larger AoP compared with the women who required cesarean section over time (Table 2). For HPD measurements, the cesarean delivery group showed significantly longer distance than did the vaginal delivery group (Table 2). Accounting for MLA, the vaginal delivery group showed comparable measurements to the cesarean delivery group initially (T1: 55.27±27.36 vs. 60.09±27.93°; P = 0.201), whereas from three hours afterward, a significantly narrower angle was observed among the women who achieved vaginal delivery (T2: 47.42 ± 27.36 vs. 68.18±25.49°, P<0.001; T3: 38.96 ± 24.37 vs. 63.18 ± 30.79°; P=0.004) (Table 2).