[Influencing factors and antenatal assessment of the vaginal birth after cesarean section]

Objective: To explore the influencing factors of the vaginal birth after cesarean section (VBAC), and establish a model for predicting the risk of trial of the trial of labor after cesarean section (TOLAC). Methods: From January 2016 to December 2018, total 694 pregnant women who underwent TOLAC in Northwest Women's and Children's Hospital were retrospectively analyzed. Those cases were divided into two groups according to the mode of delivery: the VBAC group and the failed TOLAC group. At the same time, 700 cases in the elective repeat cesarean section (ERCS) group were randomly selected as control group. The influencing factors of VBAC were analyzed by univariate and multivariate logistic regression, and the pregnancy outcomes between the three groups were compared. Results: (1) The VBAC rate was 76.1% (528/694) and 166 women underwent the failed TOLAC (23.9%, 166/694). (2) Univariate analysis found that, the pre-pregnancy body mass index (BMI) [(22.0±3.0), (23.3±2.7) kg/m(2)], the previous vaginal delivery history [10.4%(55/528), 3.6%(6/166)], the cervical score (5.2±1.9,4.3±1.6) and the neonatal birth weight [(3 315±468), (3 484±274) g] of the VBAC group were significantly different from the failed TOLAC group (P<0.05). (3) The comparison of pregnancy outcomes: the neonatal birth weight was (3 315±468) g, and the intrapartum hemorrhage volume was (255±121) ml in the VBAC group, which were significantly lower than those in the failed TOLAC group [intrapartum hemorrhage (325±173) ml] and the ERCS group [(3 572±344) g, (281±125) ml], there were statistically significant differences in the comparison among the three groups (all P<0.05). Two cases of bladder injury occurred during cesarean section in the TOLAC failure group (1.2%,2/166). The rates of the blood transfusion, puerperal infection, 5-minute Apgar score and neonatal ICU admission among the three groups were no statistically significantly different (all P>0.05). There was no maternal or perinatal death. (4) Multivariate logistic regression analysis showed that the delivery age of pregnant women (OR=0.92, 95%CI: 0.87-0.98), pre-pregnancy BMI (OR=0.92, 95%CI:0.86-0.98), vaginal delivery history (OR=3.31, 95%CI: 1.35-8.01), cervical score (OR=1.29, 95%CI: 1.13-1.42) and the birth weight of the neonates <3 300 g (OR=3.15, 95%CI: 2.02-4.90) were independent influencing factors for VBAC. The area under curve of the receiver operating characteristic curve was 0.74. Conclusions: The influencing factors of VBAC are delivery age, pre-pregnancy BMI, vaginal delivery history, cervical score and neonatal birth weight <3 300 g. The adequate individualized management and assessment of the TOLAC may be helpful to improve the VBAC rate.