Background Information
Definition
A perineal tear is a laceration or injury to the skin and soft tissues between the vaginal opening and the anus (the perineum) that occurs during childbirth.
Classification
Perineal tears are classified into 4 degrees based on the anatomical structures involved in the injury:
| Degree | Definition (involved structure in injury) |
|---|---|
| 1st | Perineal skin and/or vaginal mucosa only |
| 2nd | Perineal muscle involved (but not anal sphincter) |
| 3rd | Anal sphincter complex involved
Further subdivided into:
|
| 4th | Entire anal sphincter complex (EASExternal anal sphincter + IASInternal anal sphincter) PLUS anorectal mucosa |
Obstetric anal sphincter injuries (OASIS) is the collective term that encompasses both 3rd and 4th degree perineal tears
Note that if a tear involves the rectal mucosa but the anal sphincter complex remains intact, it is not classified as a fourth-degree tear or OASIS.
Instead, it is defined as a rectal buttonhole tear.
Aetiology
Risk factors that increase the chance of a 3rd or 4th degree perineal tear:
- Asian ethnicity
- Nulliparity
- Birthweight >4 kg
- Shoulder dystocia during delivery
- Occipito-posterior position
- Prolonged secondary stage of labour
- Instrumental delivery (highest risk seen in forceps delivery without episiotomy)
- Previous history of OASISObstetric anal sphincter injuries
It is important to note that these factors do not allow for the accurate prediction of which women will actually sustain a tear.
Clinical Features
Immediate physical signs:
- Visible anatomical trauma extending through the perineal structures (depending on the severity of the tear)
- Bleeding from the injured perineal tissues
Severe perineal tears may cause distressing pelvic floor and bowel symptoms:
- Anal incontinence (involuntary loss of flatus and/or faeces)
- Faecal urgency and other defaecatory symptoms
- Perineal pain and irritation
- Dyspareunia
If a severe perineal tear is not recognised and adequately repaired, it can lead to rectovaginal and anovaginal fistulae
Detection and Diagnosis
Clinical diagnosis
RCOG recommends that all women having a vaginal delivery should be examined systemically, including a digital rectal examination
Endoanal ultrasound is NOT routinely recommended as it does not significantly increase the detection rate of 3rd and 4th degree tears compared to a standard clinical examination.
Prevention
RCOG recommends the following points to prevent 3rd and 4th degree perineal tears:
- If episiotomy is indicated, use the mediolateral technique (60 degrees away from midline)
- In instrumental deliveries, consider mediolateral episiotomy (the risk of severe perineal tears is higher if episiotomy is not performed)
- Interventions at stage 2 labour:
- Perineal protection at crowning
- Crowning: when the baby's head is emerging from the vaginal canal
- Perineal protection: hand is placed on the perineum to provide stability and support as the head crowns. Supports the perineum and slows down the birth process to avoid sudden forceful stretching
- Warm compression
Warm compresses are typically applied directed to the perineum (area between vaginal opening and the anus).
Mechanism: Increased tissue elasticity (warmth increases blood flow and softens perineal tissue)
- Perineal protection at crowning
Management
1st and 2nd Degree Tears
1st and 2nd degree tears can be managed in the labour/delivery suite (repair in the operating theatre is not routinely required)
- Ensure adequate analgesia
- Perform suturing under LALocal anaesthetic
- 1st degree → skin suturing to improve healing (unless the skin edges are well opposed)
- 2nd degree → perineal muscle suturing
3rd and 4th degree tears
3rd and 4th degree tears (OASISObstetric anal sphincter injuries ) should be repaired in the operating theatre (under GA / LA) by a trained clinician
If there is excessive bleeding → perform vaginal packing and take to theatre ASAP
Post-repair management (only applies ot 3rd and 4th degree tears):
- Perform a digital rectal examination after the repair to ensure sutures have not been inserted through the anorectal mucosa
- Broad-spectrum antibiotics (to reduce risk of infection and wound dehiscence)
- Laxatives (to reduce risk of wound dehiscence)
- Do not routinely give bulking agents with laxatives
- Review 6-12 weeks postpartum + physiotherapy