Introduction Obstetric anal sphincter injuries (OASIS) are a serious complication of vaginal deliveries and can lead to faecal and urinary incontinence. Women, who have sustained OASIS in a previous pregnancy, undergo routine assessment to decide the appropriate mode of delivery in subsequent pregnancies. Many of these women are advised to, or opt for vaginal delivery.

Objective To evaluate the risk of subsequent perineal trauma in women who deliver vaginally following OASIS in previous delivery.

Methods This retrospective study analysed 88 women between April 2007 and April 2012 who had sustained anal sphincter damage during an index pregnancy and had a subsequent pregnancy and delivery.

Results 64 (72.8%) had an instrumental delivery and 24 (27.2%) had a spontaneous vaginal delivery (SVD) in their index pregnancy. In the instrumental delivery group, 21 (32.8%) women had a subsequent Caesarean section delivery (18 elective Caesarean, 3 emergency Caesarean) while 43 (67.2%) women had a vaginal delivery. In the SVD group, 8 (33.3%) women had a Caesarean delivery (6 elective, 2 emergency) while 16 women (66.7%) had a vaginal delivery. Out of the 59 women who had a vaginal delivery, 7 (11.9%) sustained repeat 3rd degree tear, 32 (54.2%) had 2nd degree tear, 7 (11.9%) had episiotomy, 4 (6.8%) had first degree tear, 9 (15.2%) had intact perineum.

Discussion Most women with previous anal sphincter injury sustained a second degree tear while nearly 12% had a recurrent third degree tear.