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Cohort study
Mediolateral episiotomy significantly reduces the risk of obstetric-associated anal sphincter injury (OASIS) in women who deliver via vacuum extraction
  1. Adil E Bharucha,
  2. David Prichard
  1. Mayo Clinic, Rochester, Minnesota, USA
  1. Correspondence to: Dr Adil E Bharucha, Mayo Clinic, Rochester, MN 55905, USA; bharucha.adil{at}

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Approximately 10% of women sustain obstetric-associated anal sphincter injury (OASIS) during vaginal delivery.1 Obstetric trauma is the most common cause of anal sphincter injury. Preventing OASIS is critical because between one-thirds and two-thirds of women with OASIS develop faecal incontinence (FI) with profound consequent physical and psychological effects. Primiparity, excess birth weight, vacuum extraction, forceps and median episiotomy are identified risk factors for OASIS; evidence implicating other factors (mediolateral episiotomy and epidural analgesia) is mixed, providing this study's impetus.


This manuscript comprises a retrospective analysis of risk factors for OASIS, identified during vaginal delivery among primiparous women in the Danish Medical Birth Registry. Most maternal (age, pre-pregnant body …

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  • Competing interests None.