Risk of repeat cesarean delivery in women undergoing trial of labor: A population-based cohort study.

INTRODUCTION: To consult women on best mode of delivery after a first cesarean section, more knowledge regarding risk for a repeat unplanned cesarean is needed. We investigated the association between indication of first cesarean and cervical dilation during labor preceding the first cesarean and risk of repeat cesarean in women undergoing trial of labor.

MATERIAL AND METHODS: A population-based cohort study using electronic medical records of all women delivering in the Stockholm-Gotland region, Sweden, between 2008 and 2014. The population consisted of 3116 women with a first cesarean undergoing a trial of labor with a singleton infant in cephalic presentation at ≥37 weeks of gestation. Relative risks (RR) with 95% CI were estimated using Poisson regression analyses.

RESULTS: Women with a first unplanned cesarean had higher risk of repeat cesarean compared with women with elective first cesarean (35.7% vs 20.7%, adjusted RR 1.64, 95% CI 1.43-1.89). In women with a cesarean due to dystocia, increasing cervical dilation in first labor decreased the risk of repeat cesarean in second labor. The adjusted RR of repeat cesarean was 2.48 with dilation ≤5 cm, 1.98 with dilation 6-10 cm, and 1.46 if fully dilated.

CONCLUSIONS: Almost 70% of all women eligible for trial of labor after cesarean had a vaginal birth, even women with a history of labor dystocia had a good chance of success. A greater cervical dilation in the first delivery ending with a cesarean was not in vain, since the chance of vaginal birth in the subsequent delivery increased with greater dilation.