Identifying and Managing Obstetric Anal Sphincter Injuries

OASIs are among the most serious maternal complications, yet they often remain hidden — underdiagnosed, underreported and undertreated.

What is an OASI?

Obstetric Anal Sphincter Injury (OASI) refers to third- and fourth-degree perineal tears sustained during vaginal birth — injuries that extend to the anal sphincter and in severe cases, the rectal mucosa.

The hidden cost to mothers and the NHS

Each year in the UK, more than 14,000 women experience a severe perineal tear during childbirth. But the true number is likely far higher because many injuries go unseen, unrecognised, or misclassified in the moments after birth.

3.1%

of all vaginal births result in a recorded OASI, though real rates may approach 10%.

20%

of cases, the OASI was missed at delivery.

£465k

is the average cost of an OASI if a legal claim is incurred.

The challenge beneath the surface

Severe perineal injuries are not always visible at the time of birth. Missed or misclassified OASI can have lifelong consequences — but it often begins with a moment of uncertainty in the delivery room.

Missed or Misdiagnosed Injuries

A Systemic Gap in Detection

A Culture of Fear

Beyond the tear: why it matters

OASIs are a subject that touches every part of maternity care. They affect women and birthing people on a deeply personal level and the impact can last a lifetime. For clinicians, prevention and early recognition places real demand on teams who are working to provide safe, consistent care.


Physical and mental impact


Inequalities in UK maternity care


Financial and societal impact


personal and family costs

Support for maternity professionals: you don’t have to carry it alone.

Working in maternity care is a deeply rewarding calling — but it also exposes you to births and outcomes that can be traumatic, emotionally heavy, or overwhelming. 

When challenging experiences mount up, many professionals may experience vicarious trauma, compassion fatigue, or symptoms of PTSD — and yet feel isolated or ashamed to reach out.

Our partner, Make Birth Better’s “Trauma Support for Professionals” offers a safe space, resources, and guidance designed especially for professionals in maternity settings.

Visit Make Birth Better: Trauma Support for Professionals →

RCOG OASI Care Bundle 

Developed between the RCOG, Royal College of Midwives, London School of Hygiene and Tropical Medicine and Croydon Health Services NHS Trust.

The OASI Care Bundle provides maternity teams with a practical, evidence-based framework to prevent, detect, and manage obstetric anal sphincter injuries. 

Explore the OASI Care Bundle → 

OASI Symposium at RCOG 2025

Obstetric Anal Sphincter Injuries: Time for reappraisal

“As faecal incontinence can have a devastating effect on quality of life, we need to first strive towards making missed OASIs a never event.”

– Prof Abdul Sultan

Ready to take the next step in OASI care?

We believe best practice should be practical. ONIRY brings AI innovation together with real-world usability to support confident, consistent OASI detection — helping teams turn guidance into everyday excellence.

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