The Impact of Previous Pregnancy on Obstetric Anal Sphincter Injuries in Subsequent Birth

There are four groups of women in this study. 1) Those who have had a vaginal delivery (VD) after a previously failed operative vaginal delivery (FOVD) with resultant emergency caesarean section at second stage of labour (n = 52). These women have previously experienced the effects of both pregnancy and labour up to second stage, including active pushing on the perineum resulting in stretching and swelling of the perineum before caesarean section (CS). 2) Those having their second child vaginally having had a prior elective caesarean section (ELCS) (n = 139). These women have experienced the effects of pregnancy, including the increased intra-abdominal pressure on the pelvic floor but not the effects of labour. 3) Those having a second VD (n = 1554) who maintained an intact perineum during their first VD. These women have experienced previous pregnancy, labour and vaginal delivery. These three groups were compared to the fourth control group. 4) Primiparous women (n = 19,790) having their first child vaginally. These have had no other effect on the perineum apart from their current first pregnancy.