Vaginal Birth

What is OASI – Obstetric Anal Sphincter Injury

We answer what OASI is and why is the fourth recommendation in the Birth Trauma Inquiry report is so concerning.

This post discusses injury related to birth / obstetric interventions.

The recently published Birth Trauma Inquiry report outlines 12 key recommendations to reduce the rates of birth trauma in the UK.

Recommendation #4:

Roll out and implement, underpinned by sufficient training, the OASI (obstetric and anal sphincter injury) care bundle to all hospital trusts to reduce risk of injuries in childbirth.


What is an OASI?

“An OASI is an obstetric anal sphincter injury that can occur during vaginal birth, also referred to as severe perineal tearing or third- and fourth-degree tears. Most women and birthing people who have an OASI detected and repaired at birth recover well, although it can take some time.” RCOG, UK


What is the OASi care bundle?

A set of interventions used together with the intention to reduce OASI including:

What is the evidence being used to roll out this recommendation?

The OASI1 project evaluated 55,060 live singleton vaginal births across 16 participating maternity units between Jan 2017-March 2018 and showed that through adoption of the care bundle, overall OASI rates were reduced from 3.3% before the project started to 3.0% upon its conclusion.

The evaluation showed that use of the care bundle had no effect on episiotomy and caesarean birth rates.


What are the concerns?

A universal one-size-fits all approach is a red flag in itself- what is right for one person is not always going to be right for another and could in fact be detrimental to them and their birthing experience.

The lack of significant impact on OASI incidence (3.3% down to 3%) in the study (or one less person for every 333 needing treatment) being used is another.

Many maternity care experts and supporters highlight the following evidence-based considerations have not been taken into account to reduce OASI:

  • Place of birth (inc. in water)
  • Supporting optimal positioning in labour and birth
  • Antenatal education for parents to support their own physiology

You are expecting a baby, what do you need to do about the OASI care bundle?

You can ask your midwife ahead of your birth about the implementation of the OASI care bundle at your hospital Trust.

Do further research as needed so you are fully informed and indicate on your birth preferences document as to whether:

  • You consent to the OASI care bundle being used
  • You do not consent to the OASI care bundle
  • You would like to leave it open until the time, but that consent MUST be given by you before any element of the OASI care bundle is implemented
  • You will ask if you would like any of the OASI Care Bundle support to be implemented at the time of birth but you would not like to be offered it at any point until YOU ask

What is your experience of the OASI care bundle?

We are keen to hear from professionals (midwives, obstetricians, doulas and any other maternity-related supporters) and parents to hold a constructive conversation and provide feedback to the inquiry.

Please email with your feedback and thoughts or share them on this Instagram post / via DM:

Resources to inform yourself on the OASI care bundle:


Sign up for the FREE ‘Preparing to give birth with the NHS’ recorded workshop

Includes a 30 minute video workshop and printable checklist to help you to prepare for giving birth within a stretched maternity care system. Find out more here or complete the form to register: