Study population
A total of 208 nulliparous women were recruited into our study. We excluded 27 women who decided elective cesarean delivery for the following reasons: changed their minds and rejected attempting to a vaginal delivery after an MRI examination (n = 25), pre-eclampsia (n = 2). Of the eligible 181 women, twenty-nine were excluded for immediate urgency situation of fetal compromise, one was excluded for incomplete data and one withdrew her consent (Figure S1). Table 1 illustrates the baseline clinical characteristics, MRI measurements for the study population. Of the remaining 150 women for analysis, the mean age was 30 years and the mean height was 158 cm. Sixty-two women required cesarean delivery (41%), while eighty-eight women (59%) underwent vaginal delivery: among these, 12 women (8%) were performed assisted operative deliveries using forceps and 76 (51%) achieved spontaneous vaginal delivery.