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Risk of obstetric anal sphincter injury among women who birth vaginally after a prior caesarean section: A state-wide cohort study
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  • Jessica Uebergang,
  • Richard Hiscock,
  • Roxanne Hastie,
  • Anna Middleton,
  • Natasha Pritchard,
  • Susan Walker,
  • Stephen Tong,
  • Anthea Lindquist
Jessica Uebergang
Mercy Hospital for Women

Corresponding Author:[email protected]

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Richard Hiscock
University of Melbourne, Mercy Hospital for Women
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Roxanne Hastie
University of Melbourne, Mercy Hospital for Women
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Anna Middleton
University of Melbourne, Mercy Hospital for Women
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Natasha Pritchard
Mercy Hospital for Women
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Susan Walker
University of Melbourne
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Stephen Tong
University of Melbourne
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Anthea Lindquist
University of Melbourne, Mercy Hospital for Women
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Abstract

Objective: Vaginal birth after caesarean (VBAC) has been suggested to be associated with an increased risk of obstetric anal sphincter injury (compared with primiparous women who birth vaginally). However, prior studies have been small, or used outdated methodology. We set out to validate whether the risk of obstetric anal sphincter injury among women having their first VBAC is greater than that among primiparous women having a vaginal birth. Design: State-wide retrospective cohort study. Setting: Victoria, Australia. Population: All births (455,000) between 2009-2014. Methods: The risk of severe perineal injury between first vaginal birth and first vaginal birth after previous caesarean section was compared, after adjustment for potential confounding variables. Covariates were examined using logistic regression for categorical data and Wilcoxon rank-sum test for continuous data. Missing data were handled using multiple imputation; the analysis was performed using regression adjustment and Stata v16 multiple imputation and teffects suites. Results: Women having a VBAC (n=5,429) were significantly more likely than primiparous women (n=123,353) to sustain a 3rd or 4th degree tear during vaginal birth (7.1 vs 5.7%, p<0.001). After adjustment for mode of birth, body mass index, maternal age, infant birthweight, episiotomy and epidural, there was a 21% increased risk of severe perineal injury (relative risk 1.21 (95%CI 1.07 – 1.38)). Conclusions: Women having their first vaginal birth after caesarean section have a significant increased risk of sustaining a 3rd or 4th degree tear, compared with primiparous women having a vaginal birth. Patient counselling and professional guidelines should reflect this increased risk.
27 Aug 2021Submitted to BJOG: An International Journal of Obstetrics and Gynaecology
31 Aug 2021Submission Checks Completed
31 Aug 2021Assigned to Editor
01 Sep 2021Reviewer(s) Assigned
28 Sep 2021Review(s) Completed, Editorial Evaluation Pending
20 Oct 2021Editorial Decision: Revise Major
30 Nov 20211st Revision Received
30 Nov 2021Submission Checks Completed
30 Nov 2021Assigned to Editor
30 Nov 2021Review(s) Completed, Editorial Evaluation Pending
14 Dec 2021Editorial Decision: Accept
Jul 2022Published in BJOG: An International Journal of Obstetrics & Gynaecology volume 129 issue 8 on pages 1325-1332. 10.1111/1471-0528.17063