Obstetric anal sphincter injury after episiotomy in vacuum extraction: an epidemiological study using an emulated randomised trial approach. (9th March 2021)

• Record Type: Journal Article
• Authors: Ankarcrona, V; Zhao, H; Jacobsson, B; Brismar Wendel, S
• Is Part Of: BJOG. Volume 128:Number 10(2021)
• Page Start: 1663
• Page End: 1671
• Publication Date: 2021-03-09
• Subjects: Causal inference -- inverse treatment probability weighting -- obstetric anal sphincter injury -- propensity score; Obstetrics -- Periodicals; Gynecology -- Periodicals; 618
• DOI: 10.1111/1471-0528.16663
• Languages: English
• ISSNs: 1470-0328

Abstract

Abstract : Objective: 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. Design: A population‐based observational study. Setting: Sweden. Population: 63 654 nulliparous women delivered with vacuum extraction derived from the Swedish Medical Birth Register 2000–2011, with a live singleton baby with no known malformations in cephalic presentation in gestational week ≥34 +0, and subject to lateral or mediolateral episiotomy or no episiotomy. Methods: 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). Main outcome measures: OASIS (third‐ and fourth‐degree perineal injury) in nulliparous women delivered with vacuum extraction. Results: Episiotomy was associated with a reduction in OASIS from 15.5% to 11.8%, average treatment effect of –3.66% (95% CI −4.31 to −3.01) and NNT 27. Third‐degree perineal injuries were reduced from 14.0% to 10.9% (−3.08, 95% CI −3.71 to −2.42) with NNT 32. Fourth‐degree perineal injuries were reduced from 1.6% to 1.0 % (−0.58%, 95% CI −0.79 to −0.37) with NNT 172. Conclusions: Lateral or mediolateral episiotomy reduced the prevalence of OASIS in nulliparous women delivered with vacuum extraction, compared to women with no episiotomy. Tweetable abstract: To prevent one case of OASIS in first‐time mothers delivered with vacuum, 27 episiotomies had to be performed. Tweetable abstract: To prevent one case of OASIS in first‐time mothers delivered with vacuum, 27 episiotomies had to be performed.