Obstetric perineal injury

Definition

• Obstetric injuries are tears of the perineum, labia, vagina and cervix arising during birth, spontaneously or in association with episiotomy; third- and fourth-degree tears are termed obstetric anal sphincter injuries (OASIS).

Classification

Tears

• Grade I: skin/mucosa, II: perineal muscles.
• Grade III: sphincter, IV: also rectal mucosa.
• The subdivision is 3a <50% EAS, 3b >50% EAS, 3c IAS.

• Perineal tears are classified into four degrees (classification adopted by the RCOG among others): first-degree tears involve skin or mucosa only, second-degree tears also the perineal muscles but not the anal sphincter.
• Third-degree tears involve the anal sphincter complex (3a: less than 50% of external sphincter thickness, 3b: more than 50%, 3c: internal sphincter also torn), fourth-degree tears also the anal or rectal epithelium.

Occurrence & epidemiology

Epidemiology

• Perineal injuries are common in vaginal births, mostly first- or second-degree tears; anal sphincter injuries affect about 4 to 11% of vaginal births in the United States, while considerably lower rates are reported in other countries.

Aetiopathogenesis

Aetiology and risk factors

• Risk factors include nulliparity, forceps or vacuum birth, a large baby, certain fetal positions such as persistent occiput posterior position, maternal age and ethnicity (for example Asian ethnicity) and midline episiotomy.

Clinical features

Clinical features and complications

• Most tears heal without sequelae; severe tears can lead to prolonged pain, sexual dysfunction, pelvic floor dysfunction and incontinence.
• Anal sphincter injuries are the main cause of later anal incontinence in women; further complications are infection, wound breakdown and dyspareunia.

Diagnosis

• It is essential to recognise severe tears immediately and to determine their full extent, particularly involvement of the anal sphincter.

Keep learning in the app

Further reading (selection)

1. StatPearls: Obstetric Perineal Lacerations (NCBI Bookshelf)
2. Rambam Maimonides Med J 2017: Obstetric Anal Sphincter Injuries (OASIs) in Israel – incidence and risk factors (PMC, open access)
3. DocCheck Flexikon, Episiotomie

Cross-references