Risk of obstetric anal sphincter injuries (OASIS) and anal incontinence: A meta-analysis

Michail Sideris*, Tristan McCaughey, John Gerrard Hanrahan, David Arroyo-Manzano, Javier Zamora, Swati Jha, Charles H. Knowles, Ranee Thakar, Charlotte Chaliha, Shakila Thangaratinam

*Corresponding author for this work

Research output: Contribution to journalReview articlepeer-review

19 Citations (Scopus)


Background: Obstetric anal sphincter injuries (OASIS) are the commonest cause of anal incontinence in women of reproductive age. We determined the risk of anal sphincter defects diagnosed by ultrasound, and the risk of anal incontinence in (i) all women who deliver vaginally, (ii) in women without clinical suspicion of OASIS, and (iii) after primary repair of sphincter injury, by systematic review. Methods: We searched major databases until June 2018, without language restrictions. Random effects meta-analysis was used to obtain pooled estimates of ultrasound diagnosed OASIS and risk of anal incontinence symptoms at various time points after delivery, and of persistent sphincter defects after primary repair. We reported the association between ultrasound diagnosed OASIS and anal incontinence symptoms using relative risk (RR) with 95 % CI. Results: We included 103 studies involving 16,110 women. Of all women who delivered vaginally, OASIS were diagnosed on ultrasound in 26 % (95 %CI, 21–30, I2 = 91 %), and 19 % experienced anal incontinence (95 %CI, 14–25, I2 = 92 %). In women without clinical suspicion of OASIS (n = 3688), sphincter defects were observed in 13 % (10–17, I2 = 89 %) and anal incontinence experienced by 14 % (95 % CI: 6–24, I2 = 95 %). Following primary repair of OASIS, 55 % (46–63, I2 = 98 %) of 7549 women had persistent sphincter defect with 38 % experiencing anal incontinence (33–43, I2 = 92 %). There was a significant association between ultrasound diagnosed OASIS and anal incontinence (RR 3.74, 2.17−6.45, I2 = 98 %). Interpretation: Women and clinicians should be aware of the high risk for sphincter defects following vaginal delivery even when clinically unsuspected. This underlines the need of careful and systematic perineal assessment after birth to mitigate the risk of missing OASIS. We also noted a high rate of persistent defects and symptoms following primary repair of OASIS. This dictates the need for provision of robust training for clinicians to achieve proficiency and sustain competency in repairing OASIS.

Original languageEnglish
Pages (from-to)303-312
Number of pages10
JournalEuropean Journal of Obstetrics and Gynecology and Reproductive Biology
Publication statusPublished - Sept 2020

Bibliographical note

Funding Information:
This project was funded by the National Institute of Health Research – NIHR as part of an Academic Clinical Fellowship.

Publisher Copyright:
© 2020 Elsevier B.V.


  • Anal incontinence
  • Anal sphincter defects
  • Endoanal ultrasound
  • Faecal incontinence
  • Obstetric anal sphincter injuries
  • Primary repair
  • Systematic review

ASJC Scopus subject areas

  • Reproductive Medicine
  • Obstetrics and Gynaecology


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