{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,26]],"date-time":"2026-06-26T12:00:48Z","timestamp":1782475248481,"version":"3.54.5"},"reference-count":35,"publisher":"Wiley","issue":"10","license":[{"start":{"date-parts":[[2021,3,9]],"date-time":"2021-03-09T00:00:00Z","timestamp":1615248000000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100004359","name":"Vetenskapsr\u00e5det","doi-asserted-by":"publisher","award":["2016\u201000526"],"award-info":[{"award-number":["2016\u201000526"]}],"id":[{"id":"10.13039\/501100004359","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["obgyn.onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["BJOG"],"published-print":{"date-parts":[[2021,9]]},"abstract":"<jats:sec><jats:title>Objective<\/jats:title><jats:p>To emulate a randomised controlled trial investigating whether lateral or mediolateral episiotomy compared with no episiotomy reduces the prevalence of obstetric anal sphincter injury (OASIS) in nulliparous women delivered with vacuum extraction.<\/jats:p><\/jats:sec><jats:sec><jats:title>Design<\/jats:title><jats:p>A population\u2010based observational study.<\/jats:p><\/jats:sec><jats:sec><jats:title>Setting<\/jats:title><jats:p>Sweden.<\/jats:p><\/jats:sec><jats:sec><jats:title>Population<\/jats:title><jats:p>63\u00a0654 nulliparous women delivered with vacuum extraction derived from the Swedish Medical Birth Register 2000\u20132011, with a live singleton baby with no known malformations in cephalic presentation in gestational week\u00a0\u226534<jats:sup>+0<\/jats:sup>, and subject to lateral or mediolateral episiotomy or no episiotomy.<\/jats:p><\/jats:sec><jats:sec><jats:title>Methods<\/jats:title><jats:p>The effect of episiotomy was calculated using a causal doubly robust estimation method based on propensity scores. Results are presented as the average treatment effect and numbers needed to treat (NNT).<\/jats:p><\/jats:sec><jats:sec><jats:title>Main outcome measures<\/jats:title><jats:p>OASIS (third\u2010 and fourth\u2010degree perineal injury) in nulliparous women delivered with vacuum extraction.<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>Episiotomy was associated with a reduction in OASIS from 15.5% to 11.8%, average treatment effect\u00a0of \u20133.66% (95% CI\u00a0\u22124.31 to\u00a0\u22123.01) and NNT 27. Third\u2010degree perineal injuries were reduced from 14.0% to 10.9% (\u22123.08, 95% CI\u00a0\u22123.71 to\u00a0\u22122.42) with NNT 32. Fourth\u2010degree perineal injuries were reduced from 1.6% to 1.0 % (\u22120.58%, 95% CI\u00a0\u22120.79 to\u00a0\u22120.37) with NNT 172.<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusions<\/jats:title><jats:p>Lateral or mediolateral episiotomy reduced the prevalence of OASIS in nulliparous women delivered with vacuum extraction, compared to women with no episiotomy.<\/jats:p><\/jats:sec><jats:sec><jats:title>Tweetable abstract<\/jats:title><jats:p>To prevent one case of OASIS in first\u2010time mothers delivered with vacuum, 27 episiotomies had to be performed.<\/jats:p><\/jats:sec>","DOI":"10.1111\/1471-0528.16663","type":"journal-article","created":{"date-parts":[[2021,2,5]],"date-time":"2021-02-05T18:00:33Z","timestamp":1612548033000},"page":"1663-1671","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":28,"title":["Obstetric anal sphincter injury after episiotomy in vacuum extraction: an epidemiological study using an 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