222: Validation of the vaginal birth after cesarean (VBAC) nomogram

Abstract

To validate the VBAC prediction nomogram published by Grobman et al. (Obstet Gynecol 2007) using a different patient cohort than the MFMU cesarean delivery (CD) registry from which it was derived. Historical cohort study of term pregnant women with a single prior low transverse CD attempting a trial of labor (TOL). Maternal age, pre-pregnancy body mass index (BMI), ethnicity, prior vaginal delivery (VD), prior VBAC, and indication of prior CD were used in the nomogram to calculate the predicted VBAC success rates, which were then partitioned into deciles, and compared to actual VBAC rates. Data were analyzed using Student t-test, chi-square test and receiver operating characteristics (ROC) curve. 4853 patients with prior CD delivered between 1/2002-8/2007. 497 fit the inclusion criteria and had all data available. 259 (52.2%) had a VBAC. Prior VD, prior VBAC and non-recurrent indications were significantly more prevalent in the VBAC group comparted with the failed group. However, age, BMI and ethnicity were not different between the 2 groups. The nomogram was predictive of success (ROC: AUC 0.69, 95% CI 0.64-0.74, p<0.01). Our actual VBAC rates did not differ from the predicted ones when < 50%. Above a 50% predicted success, the achieved success rates were significantly and consistently less by 10-20% (table).TablePredicted vs. actual VBAC success ratePredicted VBAC (%)# of patientsActual VBAC (%)95% CI0-200n/an/a20-30633.334-7730-403026.6712-4640-505343.430-5850-609131.8722-4260-707441.8931-5470-806860.2948-7280-9012167.7759-7690-1005479.6366-89 Open table in a new tab We confirmed that the published nomogram is predictive of VBAC success. Its accuracy will depend on the specific population.