217 Creating a Calculator to Estimate Risk of Cesarean Delivery in Patients Undergoing Induction of Labor

To determine the characteristics associated with cesarean delivery among patients undergoing induction of labor (IOL), and to develop and validate a calculator that estimates the risk of intrapartum cesarean delivery. A retrospective chart review was performed to identify all patients with term (≥37 0/7 weeks), singleton, cephalic pregnancies who underwent IOL at an academic institution from January 2017 to December 2018. Patients with prior cesarean delivery, prelabor rupture of membranes, and spontaneous labor were excluded. The primary outcome was mode of delivery. Data on all variables of interest were abstracted and the association between each variable and mode of delivery was investigated with individual logistic regression. Variables with a significant association (p<0.1) then underwent multivariable logistic regression and stepwise selection to determine inclusion in the final model. The receiver operating characteristic curve C-statistic was calculated for the model, and bootstrap resampling was performed to obtain a bias-corrected C-statistic. There were 3905 term live births during the study period. Of these, 919 (23.5%) patients met inclusion criteria. 182 patients (19.8%) delivered by cesarean delivery. Thirteen variables of interest were found to have significant associations with mode of delivery. Six variables were included in the final model - pre-pregnancy body mass index (BMI), maternal age, gestational age, parity, total weight gain in pregnancy and modified Bishop score. The model achieved a C-statistic of 0.84 and the bias-corrected C-statistic was 0.83, thus validating the model in this population. This validated model predicts the risk of cesarean delivery during induction of labor. In contrast to an existing model, it does not include race as a predictive factor for mode of delivery, as that may reflect and perpetuate existing racial disparities in obstetrics. This user-friendly online calculator may be used as an individualized objective tool during prenatal counseling on delivery planning.