Severe perineal trauma among women undergoing vaginal birth after cesarean delivery: A population-based cohort study

To examine risk of severe perineal trauma among nulliparous women and those undergoing vaginal birth after cesarean delivery (VBAC).

This is a population-based cohort study of all births to women with their two first consecutive singleton pregnancies in Stockholm-Gotland Sweden between 2008 and 2014. Risk of severe perineal trauma was compared between nulliparous women and those undergoing VBAC with severe perineal trauma being the main outcome measure. Associations between indication and timing of primary cesarean delivery and risk of severe perineal trauma in subsequent vaginal birth were analyzed using Poisson regression analysis.

The rate of severe perineal trauma among nulliparous women and those undergoing VBAC was 7.0% and 12.3%, respectively. Compared with nulliparous women, those undergoing VBAC were significantly older, had a shorter stature, and gave birth in a non-upright position to heavier infants with larger head circumferences. The rate of instrumental vaginal delivery among nulliparous women and those undergoing VBAC was 19.3% and 20.2%, respectively (P = 0.331). An increased risk of severe perineal trauma remained after adjustments among those undergoing VBAC (adjusted risk ratio 1.42, 95% CI 1.23-1.63). Level of risk was not associated with indication (dystocia or signs of fetal distress) of primary cesarean delivery, nor how far the woman had progressed in labor (fully dilated versus planned cesarean delivery) before delivering by cesarean.

Compared with nulliparous women, those undergoing VBAC are at increased risk of severe perineal trauma, irrespective of indication and timing of primary cesarean delivery.