Abstract
ObjectivesThe objective of this study was to estimate the risk of recurrent obstetric anal sphincter injury (rOASI) in women who have suffered anal sphincter injury in their previous pregnancy and analyse risk factors for recurrence through a systematic review and meta-analysis.Data sourcesA review was performed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Searches were made in Ovid MEDLINE (1996 to May 2015), PubMed, EMBASE and Google Scholar, including bibliographies and conference proceedings.Methods of study selectionObservational studies (cohort/case–control) evaluating rOASI and risk factors were selected by two reviewers who also analysed methodological quality of those studies. Pooled odds ratios (OR) for rOASI and individual risk factors were calculated using RevMan 5.3.Tabulation, integration and resultsFrom the eight studies assessed, overall risk of rOASI was 6.3 % compared with a 5.7 % risk of OASI in the first pregnancy. The risk in parous women with no previous OASI was 1.5 %. Factors that increased the risk in a future pregnancy were instrumental delivery with forceps [OR 3.12, 95 % confidence interval (CI) 2.42–4.01) or ventouse (OR 2.44, 95 % CI 1.83–3.25), previous fourth-degree tear (OR 1.7, 95 % CI 1.24–2.36) and birth weight ≥4 kg (OR 2.29, 95 % CI 2.06–2.54). Maternal age ≥35 years marginally increased the risk (OR 1.16, 95 % CI 1–1.35).ConclusionThe overall rate of rOASI and associated risk factors for recurrence are similar to the rate and risk factors of primary OASI. Antenatal decisions could be based on assessment of foetal weight and intrapartum decisions based upon the requirement for an instrumental delivery.Electronic supplementary materialThe online version of this article (doi:10.1007/s00192-015-2893-4) contains supplementary material, which is available to authorized users.
Highlights
The incidence of obstetric anal sphincter injury (OASI) appears to be rising, with rates reported between 0.6 % in Finland [1] and 19.3 % in a primiparous population in the USA [2]
Were key potential confounding variables measured and adjusted statistically for their impact on the relationship between exposure(s) and outcome(s)? Where risk factors were analysed in women with previous OASI so that odds ratios (OR) and confidence interval (CI) calculations were feasible, we identified the study as measuring variables impacting on exposure and outcome
We found that an instrumental delivery with either forceps or ventouse, BW >4 kg, shoulder dystocia or a prior fourth-degree tear all increase the risk of recurrent OASI (rOASI) in a future pregnancy
Summary
The incidence of obstetric anal sphincter injury (OASI) appears to be rising, with rates reported between 0.6 % in Finland [1] and 19.3 % in a primiparous population in the USA [2]. A recent UK survey showed rates ranging from 0 to 8 %, with a median of 2.85 % [3], which is an increase from the previous reported rates of 1 % [4]. Another UK survey reported a trebling in the incidence of OASI from 2000 to 2012 [5]. Reported rates of recurrent OASI (rOASI) are variable, ranging from 2 % [9] to 13.4 % [10]; risk factors are poorly reported. A better understanding of the overall risk of recurrence and factors that contribute to that risk would enable women and caregivers to make better informed decisions with regards future childbearing options and mode of delivery
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