Objective: To develop and validate a predictive model assessing the risk of cesarean delivery in primiparous women based on the findings of magnetic resonance imaging (MRI) studies. Design: Observational study Setting: University teaching hospital. Population: 168 primiparous women with clinical findings suggestive of cephalopelvic disproportion. Methods: All women underwent MRI measurements prior to the onset of labor. A nomogram model to predict the risk of cesarean delivery was proposed based on the MRI data. The discrimination of the model was calculated by the area under the receiver operating characteristic curve (AUC) and calibration was assessed by calibration plots. The decision curve analysis was applied to evaluate the net clinical benefit. Main Outcome Measures: Cesarean delivery. Results: A total of 88 (58.7%) women achieved vaginal delivery, and 62 (41.3%) required cesarean section caused by obstructed labor. In multivariable modeling, the maternal body mass index before delivery, induction of labor, bilateral femoral head distance, obstetric conjugate, fetal head circumference and fetal abdominal circumference were significantly associated with the likelihood of cesarean delivery. The discrimination calculated as the AUC was 0.845 (95% CI: 0.783-0.908; P < 0.001). The sensitivity and specificity of the nomogram model were 0.918 and 0.629, respectively. The model demonstrated satisfactory calibration. Moreover, the decision curve analysis proved the superior net benefit of the model compared with each factor included. Conclusion: Our study provides a nomogram model that can accurately identify primiparous women at risk of cesarean delivery caused by cephalopelvic disproportion based on the MRI measurements.

Objectives The upper two-thirds of the vagina is most commonly affected by pelvic organ prolapse. This study aims to find a reference line proximate to the axis of this part of the vagina on MRI which is critical but lacking. Design Retrospective cross-section study Setting Two university-affiliated hospital in China (July 2018 - June 2019) Population Six hundred and fourteen women without prolapse Methods Two reference lines were introduced to compare with the upper two-thirds of the vagina on pelvic MRI: the pubococcygeal line (PCL) and a line passing through the inferior pubic symphysis to the midpoint of the third sacral vertebra (PS3L). Main outcome measures The distances and the angles between the vagina and both reference lines were measured. Results: The median distances from the distal, middle, and apical points to the PS3L were -0.5[interquartile range (IQR), -0.9 - 0.0] cm, 0.0[IQR, -0.4 - 0.6] cm, and -0.2[IQR, -0.9 - 0.0] cm, respectively, while the median distances to the PCL were 0.4[IQR, 0.0 - 0.7] cm, 2.1[IQR,1.7 - 2.5] cm, and 3.1[IQR, 2.5 - 3.7] cm, respectively. The median angle between the vagina and the PS3L was significantly smaller than that with the PCL (0.0[IQR, -4.0 - 7.0] degree vs 29.0[IQR, 23.0 - 34.0] degrees, p<.001). Conclusions: A line passing through the inferior portion of the pubic symphysis to the third sacral vertebra mostly conforms to the normal upper two-thirds of the vaginal axis.