Are women having a vaginal birth after a previous caesarean delivery at increased risk of anal sphincter injury?

Abstract

Objective To examine the incidence of obstetric anal sphincter injury in women who had a successful vaginal birth after a previous caesarean delivery (VBAC).Design Retrospective analysis of prospectively gathered data.Setting A tertiary referral university institution.Population All secundiparous women with a previous caesarean delivery who had a VBAC from 2001 to 2011.Methods Details of maternal demographics, intrapartum characteristics and outcomes were examined in cases of VBAC with accompanying anal sphincter injury.Main outcome measures Rates of obstetric anal sphincter injury and associated risk factors.Results During the study period there were 3071 trials of labour in secundiparous women with a previous caesarean delivery; 65% (1981/3071) of these had a successful VBAC. Women having a VBAC were at greater risk of anal sphincter injury than nulliparous women having a vaginal delivery over the same period (5% [98/1981] versus 3.5% [1216/34 496], P = 0.001, odds ratio 1.4, 95% CI 1.15-1.75). The rate of instrumental delivery in woman having a VBAC was 39% (771/1981). On multiple logistic regression analysis an increased rate of instrumental delivery was a strong predictor of sphincter injury (P = 0.03, odds ratio 1.15, 95% CI 1.01-1.3). When the first labours of women with sphincter injury in the VBAC group were examined, 70% (60/86) had been in labour before undergoing their caesarean delivery. ConclusionThe incidence of anal sphincter injury in women undergoing VBAC is 5% and birthweight is the strongest predictor of this. The rate of instrumental delivery in this group was also increased.Keywords Anal sphincter injury, morbidity, secundiparous, trial of labour after caesarean delivery, vaginal birth after previous caesarean delivery.Please cite this paper as: Hehir MP, Fitzpatrick M, Cassidy M, Murphy M, O'Herlihy C. Are women having a vaginal birth after a previous caesarean delivery at increased risk of anal sphincter injury ? BJOG 2014;121:1515-1520

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

“…The prevalence of severe perineal trauma among nulliparous women in this study was 7.0%, which is confirmed by statistics from the Swedish National Board of Welfare for this time period. 10 Our findings did not support this theory of Hehir, as women in our sample who had a primary cesarean at full dilation had a similar risk of severe perineal trauma as women with a planned primary cesarean delivery. 6,[9][10][11][12] The explanation for the elevated risk among women undergoing VBAC remains unclear, but previous theories have focused on the characteristics of primary cesarean delivery.…”

“…Characteristics of primary cesarean section such as indication or timing of delivery, birthweight of first child, or interpregnancy interval did not alter the risk level of severe perineal trauma. Hehir et al 10 reported that "a large number" of women with severe perineal trauma in a subsequent vaginal delivery had progressed to an advanced stage before delivering by primary cesarean section (n = 27/60). 13 The rate of 12.3% severe perineal trauma among women undergoing VBAC in this study is within the range of 1.8%-18% reported in previous studies.…”

“…Hehir et al 10 reported that "a large number" of women with severe perineal trauma in a subsequent vaginal delivery had progressed to an advanced stage before delivering by primary cesarean section (n = 27/60). Compared with an episiotomy rate of 21%-79% in the prior studies, 6,[9][10][11] 6% of the nulliparous women and those undergoing VBAC in this study received an episiotomy at the time of delivery. This coupled with a "nulliparous" perineum could partly be responsible for the increased rate of severe perineal trauma.…”

A comparative study of obstetric anal sphincter injuries in vaginal deliveries of twins and singleton pregnancies

“…It has been demonstrated that the OASIS complicates 1.3% of natural vaginal deliveries, 3.7% of vacuum deliveries and 8.6% of forceps deliveries . Numerous studies have attempted to identify risk factors associated with OASIS following vaginal delivery of singletons . However, there has been little research involving multiple pregnancies.…”

“…studies have attempted to identify risk factors associated with OASIS following vaginal delivery of singletons. 4,5 However, there has been little research involving multiple pregnancies. Given the constant rise in twin deliveries, largely due to the increase in assisted reproductive techniques, 6 it is important to estimate perineal trauma rates in these deliveries.…”