This cohort study aimed to assess subsequent birth outcomes in women with a previous obstetric anal sphincter injury (OASI). Initially, a retrospective review of all cases of OASI between 2013–2019 was performed followed by a follow-up cohort survey to examine long-term outcomes as well as patient satisfaction. Women who experienced OASI during delivery and who later had a subsequent delivery were identified. Patients' charts were reviewed for clinical data including endoanal ultrasound assessment (EAUS). The survey included questions regarding recollection of counseling, planned mode of delivery, subsequent delivery, and anal incontinence prior to and since their last delivery (including completion of St. Mark’s incontinence score).

Out of 27,284 vaginal births during the study period, 828 (3.0%) women were diagnosed with OASI, and 247 (29.8%) had at least one documented subsequent birth. Of women assessed using EAUS, 92.5% had no defect on imaging, and a persistent defect was more likely following 3C/4th degree-tears (24%) compared to 3A/3B tears (5.3%). Regarding the subsequent delivery, 68% delivered vaginally with OASI occurring in 5.4% of deliveries. Eighty-eight responses to the survey were received with a median follow-up period of 83 months between OASI and survey completion. Anal incontinence was reported in 17.8% after the index delivery and 12% since their subsequent birth. Of those who had only vaginal births, 10% reported symptoms after the index delivery and 15% since. A St Mark’s incontinence score was performed, showing no statistically significant difference between scores for those having had vaginal deliveries vs caesarean sections compared with a two-tailed t-test (p = 0.59).

In summary, this study showed that the majority of women who have a subsequent delivery following OASI will remain asymptomatic at long-term follow-up. Furthermore, there were no statistically significant differences in incontinence scores between women who had vaginal deliveries compared to those having only caesarean sections for subsequent births. These results are important in that they may encourage clinicians to support women interested in a vaginal delivery after OASI.