Effect of a subsequent pregnancy on anal sphincter integrity and function after obstetric anal sphincter injury (OASI)

Abstract

Introduction and hypothesis Endoanal ultrasound (EAUS) and anal manometry are used in the assessment women with a history of obstetric anal sphincter injury (OASI), both postpartum and in a subsequent pregnancy, to aid counselling regarding mode of delivery (MOD). Methods A prospective observational study between 2012 to 2020 was completed. Women were reviewed 3 months postpartum following OASI and in the second half of a subsequent pregnancy. Anorectal symptoms were measured using the validated St Mark’s Incontinence Score (SMIS: asymptomatic to mild symptoms = ≤ 4). Anal manometry (incremental maximum squeeze pressure [iMSP: normal = > 20 mmHg]) and EAUS (abnormal = sphincter defect > 1 h in size) were performed. Results One hundred forty-six women were identified and 67.8% had an anal sphincter defect ≤ 1 h in size postnatally. In those with a defect ≤ 1 h, postpartum mean iMSP and SMIS significantly improved in a subsequent pregnancy (p = 0.04 and p = 0.01, respectively). In women with a defect > 1 h, there was no significant difference between the mean iMSP or SMIS score postnatally compared to a subsequent pregnancy. At both time points, significantly more women had an anal sphincter defect ≤ 1 h and SMIS of ≤ 4 (p = 0.001 and p < 0.001 respectively) compared to those with a defect < 1 h. In addition, significantly more women had an anal sphincter defect ≤ 1 h and iMSP ≥ 20 mmHg (p < 0.001). Overall, out of the 146 women included in this study, 76 (52.1%) with a defect ≤ 1 h also had an iMSP ≥ 20 mmHg and SMIS ≤ 4 at 3 months postpartum. Conclusions Women who remain asymptomatic with normal anal manometry and no abnormal sphincter defects on EAUS postnatally do not need to have these investigations repeated in a subsequent pregnancy and can be recommended to have a vaginal delivery. If our protocol was modified, over half of the women in this study could have had their MOD recommendation made in the postnatal period alone.

Follow up of women after obstetric anal sphincter injuries (OASI)—What is the role of anorectal testing?

“…Presence of defects on EAUS are associated with development of AI symptoms and supported by a strong evidence base within the literature 18 . Abnormal AM has been identified in symptomatic women with OASI and is associated with the presence of defects on EAUS 19,20 . The distinct role of AM in OASI follow‐up has previously been explored by the authors 21 …”

“…18 Abnormal AM has been identified in symptomatic women with OASI and is associated with the presence of defects on EAUS. 19,20 The distinct role of AM in OASI follow-up has previously been explored by the authors. 21 Our study identified that 66.3% (n = 894) of women in our tertiary unit were asymptomatic at 6 months following primary OASI repair.…”

Sonographic postpartum anal sphincter defects and the association with pelvic floor pain and dyspareunia

“…Other studies reporting the results of 3D‐EAUS ≥ 3 months after the primary repair of OASI have had rather varying frequencies of defects. For example, Gold et al reported a frequency of 55%, with no endosonographic evidence of tears in 31%, 28 Okeahialam et al found a defect of >1 h (>30° angle) in 32%, 29 and Cerro et al described defects in 90% and found that the extent of a residual anal sphincter defect on 3D‐EAUS was the most relevant factor correlating with symptoms of anal incontinence 15 . Similarly, using transperineal ultrasound (TPUS), Hubka et al reported a defect prevalence of 13.6% in patients diagnosed with OASI, and Shek et al found defects in 40% of patients and associated them with significant symptoms of anal incontinence 16,30 .…”

Reply

“…Dietz and Shek acknowledge that they failed to validate the 30 • criterion for significant defect using TPUS. We have shown previously using EAUS that, in the immediate postnatal period and in a subsequent pregnancy, anal incontinence symptoms and anal manometry (which correlate with anal sphincter function) are significantly worse in women with an anal sphincter defect > 30 • in comparison to those with smaller defects 6 . Moreover, we found that, in comparison to TPUS, EAUS has the strongest association with anal incontinence symptoms up to 2 years following OASI 7 .…”