Hypothesis / aims of study
An obstetric anal sphincter injury (OASI) can be a devastating consequence of vaginal childbirth, with around 3% of UK deliveries sustaining an injury of this magnitude (1). The Royal College of Obstetrics and Gynaecology (RCOG) recommends specialist assessment for all OASIs 6-12 weeks post partum (1), but this is not routinely offered and there is significant clinic variability from trust to trust.
The OASI clinic is a dedicated setting to review all OASIs 3 months post partum. This abstract will describe the clinic set up, patient cohort and presenting symptoms for women based on the first 18 months the clinic has been in operation. In addition, we will assess differences in anorectal manometry values between different classifications of OASI.
Study design, materials and methods
This is a retrospective study. A one-stop outpatient service was offered to all women who sustained OASIs in their most recent pregnancy (3 months post partum) in our trust. This was also extended to symptomatic women with 2nd degree tears, to assess for missed OASIs. The clinic consists of a consultant urogynaecologist, a consultant colorectal surgeon, a clinical scientist and a specialised pelvic floor physiotherapist. Assessment of these patients included: verbal history taken, vaginal and digital rectal examination, mobile anorectal manometry and 2D endoanal ultrasound. Manometry and endoanal ultrasound were performed with equipment from THD and conducted in accordance with their protocol. For patients where a worse grade of OASI was imaged, they were referred for 3D endoanal ultrasound. Where necessary, patients were given an initial session of pelvic floor physiotherapy at the appointment.
A one way ANOVA and post hoc Tukey were performed to assess differences between OASI classifications and their resting pressure and squeeze pressure measurements on anorectal manometry.
Results
106 patients were seen in the clinic between October 2020 and March 2022. The percentage of patients with each classification of OASI are shown in Table 1. 3B tears were the most prevalent in our clinic.
65 patients (61.3%) were asymptomatic. Of the 41 (38.7%) symptomatic patients, faecal urgency (with or without incontinence) and flatus incontinence were the most commonly reported, with 12.3% of patients experience these symptoms. 10.3% had an anal fissure. 5.6% had urinary incontinence. The least common symptom reported was dyspareunia (3.8%). In our cohort, 100% of 4th degree tears had at least one symptom, but only 20% of 3Cs were symptomatic. All non-OASI patients had missed tears. 6 patients had their initial OASI classification upgraded. 6 patients had their original OASI downgraded.
There was no significant difference for resting pressure (F ratio = 0.25, p =0.906101) or squeeze pressure ( F ratio = 1.26135, p = 0.317858). A post hoc Tukey HSD was performed for both groups and showed no significant differences between any of the groups (Table 2 shows pairwise comparisons for resting pressure).
Interpretation of results
We describe our model for a one-stop OASI service, and showcase the cohort of patients we saw in the first 18 months of out clinic in this preliminary data set. As this clinic develops, we hope it will allow patients to be counselled better regarding their injuries, and improve their symptom management long term.
This study was not designed to assess how many OASIs are missed in our unit. However, based on this preliminary data set, 100% of our patients who were initially reported as having no OASI actually had a missed tear. More work is needed to identify these patients early.
4th degree tears in this cohort were highly symptomatic, whereas 80% of 3Cs were asymptomatic. This may be due to variation in depth of the injury to the internal sphincter. This group is small in number, which may explain why there was not a spread of symptoms. Our rates of urinary incontinence were lower than previously reported (2). This can be partially explained by the fact that urinary symptoms were not originally discussed, but were added several months into the development of the clinic. In addition, we hypothesise that patient perceive urinary incontinence post partum to be a normal part of childbirth, and therefore may not report it as a problem.
There are several limitations to this study. Firstly, symptoms were not assessed using validated questionnaires. Secondly, not all patients were seen at 3 months post partum due to staff limitations and waiting lists. This additional time for healing may explain why there are no significant differences in anorectal physiology results, and why some patients appeared to have less severe OASIs than previously described.
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We intended to report our full data set in future, with the inclusion of a 1 year follow up to assess symptomatic progression and treatment outcomes.