title: Obstetric anal sphincter injuries after episiotomy: systematic review and meta-analysis.
abstract: BACKGROUND
  There is conflicting evidence on whether mediolateral episiotomy (MLE) reduces the risk of obstetric anal sphincter injuries (OASI) in spontaneous vaginal deliveries (SVD).
  
  
  OBJECTIVE
  A systematic review was undertaken to compare rates of OASI amongst women who had undergone mediolateral episiotomy versus those who did not.
  
  
  METHODS
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  METHODS
  Electronic searches were performed in literature databases: CINAHL, Cochrane, EMBASE, Medline and MIDIRS from database inception to July 2015. Studies were eligible if MLE was compared to spontaneous tears and if OASI was the outcome of interest. Two reviewers independently selected and extracted data on study characteristics, quality and results. We computed events of OASI in those who did and did not have an episiotomy from individual studies and pooled these results in a meta-analysis where possible.
  
  
  RESULTS
  Of the 2090 citations, 16 were included in the review. All were non-randomised, population based or retrospective cohort studies. There was great variation in quality amongst these studies. Data from 7 studies was used for meta-analysis. On collating data from these studies where the majority of women (636755/651114) were nulliparous, MLE reduced the risk of OASI (RR 0.67 95 % CI 0.49-0.92) in vaginal delivery.
  
  
  CONCLUSIONS
  The pooled analysis of a large number of women undergoing vaginal birth, most of who were nulliparous, indicates that MLE has a beneficial effect in prevention of OASI. An accurately given MLE might have a role in reducing OASI and should not be withheld, especially in nulliparous women. Caution is advised as the data is from non-randomised studies.
authors.affiliation: Department of Obstetrics and Gynaecology, Birmingham Women's NHS Foundation Trust, Edgbaston, B15 2TG, UK. t.s.verghese@bham.ac.uk.
authors.forename: Tina Sara
authors.initials: TS
authors.lastname: Verghese
authors.affiliation: Birmingham Clinical Trials Unit, University of Birmingham, Edgbaston, UK.
authors.forename: Rita
authors.initials: R
authors.lastname: Champaneria
authors.affiliation: Royal Bournemouth and Christchurch Hospital NHS Trust, Bournemouth, UK.
authors.forename: Dharmesh S
authors.initials: DS
authors.lastname: Kapoor
authors.affiliation: Department of Obstetrics and Gynaecology, Birmingham Women's NHS Foundation Trust, Edgbaston, B15 2TG, UK.
authors.forename: Pallavi Manish
authors.initials: PM
authors.lastname: Latthe
mesh_terms: D001003:Anal Canal / Q000293:injuries*; D016022:Case-Control Studies; D036861:Delivery, Obstetric / Q000009:adverse effects*; D004841:Episiotomy / Q000009:adverse effects*; D005260:Female; D006801:Humans; D010502:Perineum / Q000293:injuries*; D011247:Pregnancy; D012189:Retrospective Studies; D012306:Risk; D014621:Vagina / Q000293:injuries*
keywords: Mediolateral episiotomy; Obstetric anal sphincter injury; Perineum; Spontaneous vaginal delivery