Maternal characteristics
A total of 634 nulliparous women were recruited, fifteen of whom were
excluded because of incomplete data, and five withdrew due to discomfort
during the ultrasound examination. Of the remaining 614 women, 524
(85.3%) women underwent vaginal delivery and 90 (14.7%) were required
cesarean delivery. The percentage of women with fetuses in non-OA
position at the first time of ultrasound examination was 53.9% (331
cases) in our study, as 159 (25.9%) cases were in the OP position and
172 (28.0%) were OT position. The main characteristics of the
participants are shown in Table 1.