Mode of delivery following an OASIS and caesarean section rates.

Objectives: While the rate of obstetric anal sphincter injury (OASIS) is increasing, there is a lack of evidence on how best to advise women on mode of delivery (MOD) afterwards. The objectives of this study were to assess the clinical value of bowel symptoms, endoanal ultrasound and anorectal manometry in the management of pregnancies after an OASIS and evaluate the performance of different algorithms.

Study Design: This was a retrospective analysis of prospectively collected data in a university hospital perineal clinic. Women with OASIS undergoing endoanal ultrasound scan (EAUS) and anorectal manometry (AM) were included in this study (all women with an OASIS, except the asymptomatic 3a tears). A number of published algorithms were theoretically applied in this cohort to define recommended MOD after an OASIS.

Results: Out of the 233 women included in the study, 51 (21.9%) were symptomatic, 141 (60.5%) had persistent sphincter defects on EAUS and 124 (53.2%) had abnormal AM. One asymptomatic and five symptomatic women were found to have isolated internal anal sphincter (IAS) defects without external anal sphincter (EAS) defects. There were no women with low resting pressure and normal incremental squeeze pressure. The application of the algorithm requiring only one abnormal investigation to be recommended caesarean would have led to an 81.5% caesarean rate. If women with symptoms of anal incontinence or abnormal investigations would be advised for caesarean the rate would be 85.0%. Using the local protocol where symptomatic women only needed one of the two investigations to be abnormal but asymptomatic women were required to have both investigations being abnormal, 94 were considered for caesarean (40.3%).

Conclusion: There is a wide range in the number of patients recommended to have caesarean section after an OASIS, depending on the used criteria and management algorithms. There is minimal additional information gained from identifying internal anal sphincter defects and measuring low resting pressures at manometry.