Hypothesis / aims of study
Obstetric Anal Sphincter Injury (OASI) is the commonest cause of anal incontinence in young women and complicates 6% primiparous births. Lifetime incidence of anal incontinence is increased threefold after OASI compared to an uncomplicated delivery (1). In women who subsequently deliver after OASI, lifetime incidence of anal incontinence is up to 50%; risk factors include pre-existing symptoms of anal incontinence and degree of OASI (2). The risk of worsening anal incontinence after OASI is an important consideration for women choosing mode of birth in subsequent pregnancies. Despite this, there is limited evidence for a preventative value for elective Caesarean for the development of anal incontinence after OASI. Both the RCOG and AJOG recommend women should be counselled regarding birth options.
We aimed to systematically review and meta-analyse the current evidence for to determine whether elective Caesarean is protective against the development of anal incontinence after OASI.
Study design, materials and methods
A systematic review and meta-analysis was performed according our prospectively published protocol (PROSPERO CRD42022372442) adhering to PRISMA guidelines. Five databases were searched; Medline/Pubmed, Embase, Medline, CINALH and Cochrane from inception to 30th November 2022. References from included studies were hand searched. We included grey literature. All title/abstract screening, full text review, data extraction and risk of bias assessments were completed by two blinded independent reviewers. Authors were contacted to provide data in a suitable format for meta-analysis. Joanna Briggs tools were used to appraise risk of bias in cross-sectional, cohort and case-control studies and Cochrane tools for randomised-controlled trials (RCTs). Analyses were performed in Revman 5.4 using random-effects modelling if significant heterogeneity was demonstrated.
Our primary outcome of interest was the incidence of anal incontinence after a subsequent delivery by either planned elective caesarean section (CS) or planned vaginal birth (VB) in women after OASI. Secondary outcomes included solid fecal incontinence, liquid fecal incontinence, flatal incontinence, fecal urgency, quality of life, satisfaction and regret with mode of birth. We included any study which provided outcomes of interest after an OASI and a subsequent birth.
Results
2472 articles (excluding 1239 duplicates) were identified. 86 studies met inclusion criteria after full text review.
Risk of bias and data heterogeneity:
All data were at high risk of bias for at least one domain. One multicentre RCT contributed data to analyses; a large majority of included women did not have an OASI diagnosed at time of index delivery and were included after ultrasound findings on follow up (Abramowitz et al., 2021). One prospective cohort study to 6 months follow up was included (Webb et al., 2020). All other studies varied in quality and methodology and included a mixture of retrospective reviews, case-control studies, service evaluations and questionnaire studies. A wide range of methods and protocols for counselling mode of subsequent birth were described: based on patient symptoms alone; endoanal ultrasound criteria; anorectal manometry criteria; and findings on 3D transperineal ultrasound. It was not possible to analyse data for an asymptomatic group of women in isolation from symptomatic women.
Recurrence of OASI:
49 studies reported recurrence of OASI in women undergoing subsequent vaginal birth. Mean index OASI rate was 3.31% and recurrence was 6.6% (7413 cases; range 1.9-25%). Index OASI rates were higher in teaching hospitals (6.13% n=32) compared to population-based studies (4.34% n=11) and district general hospitals (3.2% n=6). Recurrent OASI rates were higher in district general hospitals (11.74% range 6.6-25% n=6) but similar in teaching hospitals (6.02% range 1.9%-13.4% n=32) and population-based studies (5.59% range 2.1-7.2% n=11).
Incidence of anal incontinence after subsequent vaginal birth:
22 studies reported our primary outcome; the incidence of anal incontinence after OASI and a subsequent birth. 12 studies (1 RCT and 11 non-randomised studies) were suitable for meta-analysis as they included data for both CS and VB in a suitable form for pooling.
The total incidence of anal incontinence after subsequent delivery after OASI may be higher after CS than VB; however the wide CI is consistent with no effect or possible harm (p=0.05; OR 1.64, 95% CI 1.00-2.70; 9 non-randomised studies, 2587 participants; high risk of bias). There was no evidence of a difference in deterioration in anal incontinence after subsequent VB compared to CS after OASI across all follow up time periods (Figure 1: p=0.25; OR 0.91, 95% CI 0.62-1.35; 9 studies, 2701 participants). There was no evidence of a difference in deterioration in anal incontinence 2+ years after subsequent birth (p=0.13; OR 0.89 95% CI 0.41-1.94; 3 non-randomised studies, 2151 participants). One study provided data for long-term outcomes via questionnaire 5-14y after subsequent birth and demonstrated a possible protective effect of CS against the development of long-term symptoms of anal incontinence (Jango et al., 2016). The study relied on retrospective recall of patient symptoms and the finding was not deemed significant on multivariate analysis by the study authors.
Anal incontinence after subsequent delivery by any mode:
Regardless of birth mode, women with OASI experience a deterioration in anal incontinence post- subsequent birth compared to symptoms pre- subsequent birth (Figure 2: p=0.04; OR 0.61, 95% CI 0.38-0.98; 13 non-randomised studies, 5600 participants).
Other outcomes:
There was no evidence of a difference in our secondary outcomes after subsequent delivery by CS or VB after OASI. No studies reported on symptoms of irritable bowel syndrome, obstructive defecation, blood loss, other adverse outcomes or length of stay.
Interpretation of results
Symptomatic women delivering after OASI were advised to undergo elective Caesarean; when looking at total incidence of anal incontinence after subsequent birth we may therefore expect more women to be symptomatic after a CS than a VB in non-randomised studies. To account for this confounder, we extracted data for a deterioration in anal incontinence (worsening anal incontinence score or development of new symptoms after subsequent birth). There is no evidence of a difference in deterioration of anal incontinence between women who deliver by CS compared to women who deliver by VB after OASI (Figure 1).
This analysis does not demonstrate a protective benefit for routine elective CS in preventing a deterioration of anal incontinence after OASI; however data are significantly limited. All included studies were at high risk of bias for at least one outcome. This was due to: limitations with the population recruited; non-randomisation to treatment outcomes; inclusion of symptomatic women causing systemic bias; retrospective analysis; failure to analyse by intention to treat (emergency caesarean group included with elective caesarean group or excluded); and a lack of robust outcome data measurement in some studies.
We recommend the need for either a RCT or a well-designed prospective cohort study recording validated symptoms after index OASI with long term anal incontinence outcomes after subsequent VB and CS. Included women should be asymptomatic and diagnosed with OASI at the time of delivery to avoid pitfalls of making retrospective diagnoses of OASI on ultrasound and to enable generalisabilty to centers which do not have access to these resources and counsel based on symptoms alone.