Obstetric Anal Sphincter Injuries

Obstetric Anal Sphincter Injuries (OASIS) – Navigating Recovery after Birth

Obstetric Anal Sphincter Injuries (OASIS), refer to severe perineal tears that affect the muscles responsible for bowel control. While not often openly discussed, these injuries can have a significant impact on physical and emotional well-being. OASIS occur in approximately 2–6% of vaginal births, with higher rates reported among first-time mothers. In Australia, the figure stands at around 3% of all vaginal births, although the true number may be higher due to underdiagnosis. With early intervention and the right physiotherapy support, many women can achieve a successful recovery.

What Are Obstetric Anal Sphincter Injuries?

OASIS refers to Grade 3 and Grade 4 perineal tears sustained during vaginal birth. These are more serious injuries involving the anal sphincter complex, which plays a key role in controlling bowel movements. OASIS can lead to serious complications in the short and long-term following birth. These injuries are the leading cause of anal incontinence and can lead to dyspareunia (pain during intercourse). Additionally, short-term consequences, include wound haematoma, abscess, and recto-vaginal fistulae formation.

Types and Grades of Perineal Tears

Perineal tears are classified into four grades, based on severity:

• Grade 1: Involves only the vaginal lining (epithelium).
• Grade 2: Extends into the perineal muscles but spares the anal sphincter.
• Grade 3: Subdivided into three categories:
  • 3a: <50% of the external sphincter is torn.
  • 3b: >50% of the external sphincter is torn.
  • 3c: Both the external and internal anal sphincters are torn.
• Grade 4: Involves the external sphincter, internal sphincter, and the anal mucosa.

Can OASIS Be Rehabilitated?

It is important to understand the difference between tears involving just the internal anal sphincter and the internal and external anal sphincter when planning treatment.

The external anal sphincter is a voluntary muscle, which means it can respond well to physiotherapy and rehabilitation. As a result, women with Grade 3a and 3b tears often achieve good outcomes with pelvic floor physiotherapy alone.

However, injuries involving the internal anal sphincter (as in grade 3c and Grade 4 tears) are more complex. The internal sphincter is involuntary and cannot be retrained with exercise. These cases will require surgical repair, alongside physiotherapy, for optimal results.

Why Early Intervention In Obstetric Anal Sphincter Injuries Matters

OASIS is a primary risk factor for both short and long-term faecal incontinence, as well as dyspareunia. Early diagnosis of the injury is crucial to determine a therapeutic strategy and avoid the development of late-onset consequences, such as faecal incontinence. The Australian Physiotherapy Association recommends beginning pelvic floor muscle training within the first month after giving birth. Early and guided physiotherapy has been shown to reduce the risk of:

• Gas leakage
• Liquid stool incontinence
• Urinary stress incontinence

Rebuilding strength, coordination, and awareness in your pelvic floor muscles is key to recovery and regaining confidence.

What Will Physiotherapy for Obstetric Anal Sphincter Injuries Involve?

A physiotherapy session for OASIS rehabilitation will involve a thorough assessment and discussion about your concerns with your physiotherapist. Tips will be given regarding daily activities, limiting pain where possible, and advice will be provided to help keep your scar clean and speed up the healing process. Your physiotherapist will then guide you through exercises to begin in the initial stages of healing. These exercises will be safely progressed as you move through the different stages of recovery.

Can OASIS Be Prevented?

While not all perineal trauma can be prevented, some antenatal techniques may help reduce the risk of OASIS, including:

• Perineal massage in the final weeks of pregnancy (after 34 weeks of pregnancy only)
• Practising pelvic floor exercises that focus on both contraction and relaxation
• Utilising optimal birthing positions and breathing strategies during labour
• Having skilled support during the pushing stage

Initially having an obstetric anal sphincter injury may feel overwhelming, but with proper diagnosis, early intervention, and ongoing support, most women go on to fully recover and regain pelvic health. If you have experienced a perineal tear or have concerns about postpartum recovery, contact your health provider to discuss physiotherapy support.