Obstetric anal sphincter injury after episiotomy in vacuum extraction: an epidemiological study using an emulated randomised trial approach

Abstract

Objective: To emulate a randomized controlled trial investigating if lateral or mediolateral episiotomy compared to 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 without 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-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.

Pelvic floor dysfunction one year after first childbirth in relation to perineal tear severity

“…A reduction in the episiotomy rate in unassisted vaginal deliveries led to an increase in second-degree injuries of anatomic damage less than or equal to that caused by episiotomy without and increased rate of severe second-degree injuries 28 . There is continuing support for the use of episiotomy in vacuum delivery in nulliparas 29 although the number needed to treat was 27, and the results from randomized controlled trials to validate these recommendations are awaited 30 . Episiotomy is an obstetric technique associated with levator injury 23 .…”

Risk factors for obstetric anal sphincter injuries during vaginal delivery: can we reduce the burden?

“…Although data from the literature show that episiotomy can reduce the prevalence of severe lacerations in assisted deliveries, the number of procedures needed to prevent one OASIS case is high [55]. Moreover, the group of patients who could benefit from episiotomy has not been identified yet.…”

“…However, the study was underpowered to prove a significant change in the OA-SIS risk, mainly due to a high rate of episiotomy (52%) in the selective use group [53,54]. Ankarcrona et al [55] evaluated 63654 nulliparous women delivered with vacuum extraction. They showed that episiotomy could reduce the prevalence of OASIS from 15.5% to 11.8%.…”

Authors' response to: “Re: obstetric anal sphincter injury after episiotomy in vacuum extraction: an epidemiological study using an emulated randomised trial approach: robustness and external validity of different practices”

“…We thank Drs Boujenah, Beddock and Harvey for their interest in our article ‘Obstetric anal sphincter injury after episiotomy in vacuum extraction: an epidemiological study using an emulated randomised trial approach’ 1,2 …”