Ultrasonographic assessment of pelvic parameters associated with mode of delivery in Turkish pregnant women

Pelvic morphology plays a crucial role in determining the course and outcome of labor. Ultrasonographic assessment offers a non-invasive and practical approach to evaluating pelvic morphology and pelvic adequacy. The aim of this study was to evaluate the relationship between ultrasonographic measurements of pelvic parameters—specifically the subpubic angle (SPA) and the obstetric conjugate diameter (OCD)— and the likelihood of vaginal delivery versus cesarean delivery due to cephalopelvic disproportion in Turkish nulliparous women. This prospective cohort study included 267 nulliparous women with singleton, cephalic pregnancies at ≥ 37 weeks of gestation. Ultrasonographic measurements were performed prior to the onset of labor to assess the SPA and OCD. Maternal, fetal, and pelvic parameters were compared between women who had vaginal delivery and those who underwent cesarean delivery due to cephalopelvic disproportion. Additionally, correlations between pelvic measurements and maternal characteristics were assessed. Of the participants, 219 (82%) had vaginal deliveries, while 48 (18%) underwent cesarean section due to cephalopelvic disproportion. Mean SPA (94.88 ± 7.52° vs. 103.64 ± 7.27°; p < 0.001) and OCD (112.38 ± 8.71 mm vs. 121.29 ± 6.62 mm; p < 0.001) were significantly smaller in the cesarean group. ROC analysis demonstrated that both the SPA and OCD had good discriminatory ability for distinguishing vaginal delivery from cesarean delivery due to cephalopelvic disproportion (AUC: 0.788 and 0.794, respectively). The optimal cut-off values were 100.24° for SPA (81.3% sensitivity, 61.6% specificity) and 116.71 mm for OCD (81.3% sensitivity, 71.2% specificity). Cesarean delivery rates were significantly higher among patients with SPA and OCD values below these cut-off thresholds. A weak positive correlation was found between SPA and OCD ( r = 0.269, p = 0.011), while maternal age, BMI, height, and gestational age showed no significant associations with pelvic measurements. A narrower subpubic angle and a shorter obstetric conjugate diameter, as measured by ultrasonography, were associated with cesarean delivery. These findings suggest that ultrasonographic pelvic measurements may provide useful, non-invasive information and may complement conventional obstetric assessment.