Method

Systematic review and meta-analysis were performed according to our prospectively published protocol (PROSPERO CRD42022372442) using PRISMA guidelines (20). Authors were contacted to provide data in a suitable format for meta-analysis if not supplied. Core outcome sets for OASI have not been published, but there are published protocols in development seeking to establish this for OASI (21), perineal trauma (22) and the effects of episiotomy and OASI (23). Patients and the public were not directly involved in conducting this review.

Eligibility criteria

Participants/Population:

All women >18y who have had an OASI and a subsequent birth by any mode. OASI is defined as a 3rd or 4th degree tear by the Sultan classification (24). Inclusion and exclusion criteria are described (S2).

Intervention:

Planned elective CS in a subsequent birth after an OASI, analysed by intention-to treat. Observational studies comparing vaginal birth to all CS (emergency and elective) included with risk of bias assessment.

Comparison:

Planned vaginal birth. Emergency CS was analysed with vaginal birth outcomes via intention-to-treat when possible. When data were not provided (i.e. when emergency CS was included with planned CS) the study is included with risk of bias assessed.

Outcomes:

Our primary outcome is AI (solid, liquid, flatus) after subsequent birth by any mode; including but not limited to; St Marks Score, Wexner score, EPAQ, clinical description. AI outcome is stratified by time if available: ≤2y and ≥5y.
Subgroup analysis for patients asymptomatic after index birth.
Our secondary outcomes are: QOL, regret with MOB choice, satisfaction with MOB choice, fecal urgency, obstructive defecation, change in AI pre- and post- subsequent birth, AI in women after subsequent birth vs no subsequent birth, repeat OASI rate and adverse events (return to theatre, organ injury).

Measures of effect

Dichotomous outcomes are presented as risk ratio/odds ratios with 95% CI. Continuous outcomes presented as mean difference with 95% CI.

Search strategy

MeSH subject heading and database-specific truncated search terms were used to avoid excluding potential studies. Three concepts were implemented for the search strategy: (1) identification of all types of anal sphincter or anal canal injury, (2) identification of all subsequent birth by any mode and (3) identification of all types of anal incontinence. The search terms and strategy are detailed (S1).

Information sources

Search strategy was executed in Ovid MEDLINE/PubMed 1946-2022 (Ovid), Embase 1974-2022 (Ovid), CINAHL(EBSCOhost) 1937-2022, Cochrane Combined 1996-2022, Clinical trials and Google Scholar from inception to 1st December 2022.

Study selection

Setting

We included randomised-controlled trials and non-randomised studies including observational, cohort, cross-sectional, case-control and retrospective reviews in any publication format which provided data for our outcomes of interest for a birth after OASI (Table S1).

Data extraction (selection and coding)

All title and abstract screening (EC, RH), full text review (EC, RH), data extraction (EC, KA, RH) and risk of bias assessments (EC, RH), were completed by two blinded independent reviewers according to standard Cochrane methodology. Screening took place using Rayyan review software (25). Discrepancies were resolved by a third reviewer (RK). We describe characteristics of included studies in Table S1.

Risk of bias assessment

Risk of bias was undertaken using the ROBINS-I tool (26).

Strategy for data synthesis

Dichotomous outcomes were meta-analysed in RevMan 5.4 and are presented as risk ratio/odds ratios with 95% confidence intervals. Continuous outcomes are presented as mean difference with 95% confidence intervals. When significant statistical heterogeneity was demonstrated on meta-analysis (including but not limited to I²>40%) random effects modelling is used for meta-analyses. Studies providing data on incidence of AI are included in the ‘total AI’ meta-analysis, whilst studies demonstrating a change in AI score or the development of new AI symptoms in previously asymptomatic women after a subsequent birth after OASI are included in the ‘new or worsening AI’ meta-analysis.
Subgroup analysis
Women who were symptomatic of anal incontinence after the first birth vs those who were asymptomatic.