External validation of calculator for cesarean delivery during induction of labor

To validate a published risk calculator to predict cesarean delivery (CD) among singletons undergoing induction of labor.

Our retrospective cohort study included singletons undergoing induction of labor. A predicted CD score was calculated for each individual based on a previously developed calculator. External validation of the calculator was assessed by the discriminative power of the model by using the area under the receiver operating characteristic curve, and by a calibration curve. The score was categorized as less than 10%, 10% to less than 30%, and 30% or greater. The primary outcome was CD. The secondary outcomes were a composite maternal adverse outcome (CMAO) and composite neonatal adverse outcome (CNAO). Multivariable Poisson regression models with robust error variance were used to estimate the association; adjusted relative risks with 95% confidence interval (CI) were calculated.

Among 548 women, 159 (29%) had CD. The area under the curve was 0.77 (95% CI 0.73-0.81), and the calibration curve and its 95% confidence band demonstrated good calibration. The likelihood of having a CD was higher in those with a score from 10% to less than 30% (adjusted relative risk [aRR] 2.65, 95% CI 1.58-4.45) and 30% or greater (aRR 5.73, 95% CI 3.55-9.25). The risk of CMAO was higher in those with a score between 10% and less than 30% (aRR 1.64, 95% CI 1.08-2.48) and 30% or greater (aRR 1.81, 95% CI 1.20-2.73). The risk of CNAO was similar across groups.

The previously developed prediction model demonstrated good external validity in our cohort. Our analyses suggest that a higher predicted CD score was associated with an increased likelihood of CD and CMAO.