Trial of Vaginal Birth After Cesarean (VBAC): External validation of the Polish prediction indices of the VBAC

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Abstract
Background Vaginal birth after cesarean section (VBAC) is a safe option for both mothers and children. Currently available prediction tools have not been validated in the Polish population. Dobrowolska-Redo proposed a model for predicting VBAC success, and the aim of this study was to evaluate its clinical utility. Methods This retrospective analysis of data collected from 462 pregnant women with a history of one previous cesarean section, all qualified for a VBAC attempt. Deliveries occurred between January 1, 2021, and December 31, 2023, at the II Department of Obstetrics and Gynecology, Medical University of Warsaw. Inclusion criteria were: previous low transverse cesarean section, singleton pregnancy, no indication for elective cesarean delivery, and live birth. Ethical approval was granted by the local committee (reference no. AKBE/300/2024). The data were anonymized before analysis. Results Among the cohort of 462 women, 271 (58.7%) had successful VBAC, whereas 191 (41.3%) underwent intrapartum cesarean section. The prediction model for preterm births (pTi) showed no clinical utility. The median Ti score differed significantly between the VBAC group and the cesarean group. Removing two parameters (manual labor and place of residence) improved model performance. Higher BMI increased the likelihood of cesarean delivery, both before pregnancy (23.43 vs. 24.54 kg/m²; p = 0.006) and at delivery (27.99 vs. 29.36 kg/m²; p = 0.007). Prior vaginal birth was a strong predictor of successful VBAC (31.5% vs. 11.2%; p = 0.000), as was a history of fetal macrosomia (15.5% vs. 8.7%; p = 0.047). Gestational diabetes was more common in women who ultimately required cesarean delivery (34.2% vs. 23.7%; p = 0.023). Epidural anesthesia use correlated with a lower cesarean rate (26.6%; p = 0.000). Conclusions In this single-center cohort, the Polish index model for full-term VBAC (Ti) prediction showed moderate accuracy. A refined version demonstrated improved performance compared with the original. Several predictors of successful VBAC were confirmed, including prior vaginal delivery and history of macrosomia, while high BMI and gestational diabetes increased the risk of intrapartum cesarean section. Trial registration Retrospectively registered.

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