Mediolateral Episiotomy Should Be Performed Over Midline Episiotomy
When episiotomy is indicated during labor, perform a mediolateral episiotomy at a 60-degree angle from the midline, as it significantly reduces the risk of severe perineal trauma (obstetric anal sphincter injuries - OASI) compared to midline episiotomy, which carries a substantially higher risk of anal sphincter damage.
Key Recommendation
The 2020 RCOG guideline clearly states that mediolateral episiotomy should be discussed with women as part of preparation for assisted vaginal birth, and when performing it, the cut should be at a 60-degree angle initiated when the head is distending the perineum 1.
Evidence-Based Rationale
Why Mediolateral Over Midline:
Protection Against Severe Tears:
- Large observational data from the Netherlands (28,732 assisted vaginal births) demonstrated mediolateral episiotomy is protective against OASI in both vacuum extraction (9.4% vs 1.4%; OR 0.11) and forceps birth (22.7% vs 2.6%; OR 0.28) 1
- A 2007 study showed midline episiotomy resulted in 14.8% deep perineal tears versus only 7% with mediolateral episiotomy 2
- Historical data from 1980 confirmed anal sphincter injury was significantly more common after midline procedures 3
Strongest Benefit in Specific Populations:
- Evidence is particularly strong for nulliparous women and forceps deliveries 1
- A 2022 propensity-score analysis found mediolateral episiotomy reduced OASI rates in forceps/spatula delivery (2.3% vs 6.8%, RR 0.38) and vacuum delivery (1.3% vs 3.4%, RR 0.27) 4
When to Use Episiotomy:
Restrictive, Not Routine Approach:
- Use episiotomy selectively based on clinical circumstances and patient preferences, not routinely 1
- The Cochrane review supports restrictive over routine episiotomy policies, showing less posterior perineal trauma, less suturing, and fewer healing complications 5
Strongest Indications:
- Assisted vaginal births (forceps or vacuum) in nulliparous women 1, 6
- Forceps deliveries show 6.53-fold greater risk of OASIS without episiotomy 1
- Fetal distress situations where expedited delivery is needed 4
Technical Execution
Proper Technique:
- Angle: 60 degrees from midline toward the ischial tuberosity 1, 7
- Timing: Initiate when fetal head is distending the perineum 1
- Starting point: Within 3 mm of midline in posterior fourchette 7
Important Caveats
Acknowledge Trade-offs:
- One UK study found episiotomy associated with increased postpartum hemorrhage (28.4% vs 18.4%) 1
- Episiotomy complications include perineal pain, dyspareunia, and sexual dysfunction 6
- More anterior perineal trauma occurs with restrictive episiotomy policies (RR 1.84) 5
Avoid in Multiparous Women:
- Evidence shows increased OASI risk in parous women with episiotomy (OR 1.27) 1
- Benefits are primarily in nulliparous populations
Never Perform Midline:
- Midline episiotomy carries unacceptably high risk of anal sphincter injury 2, 3
- Risk factors compound with primiparity, maternal height <145 cm, birthweight >3,500g, and forceps use 2
Clinical Algorithm
- Assess parity: Nulliparous = stronger indication; multiparous = generally avoid
- Evaluate delivery mode: Forceps > vacuum > spontaneous for episiotomy benefit
- If episiotomy indicated: Always choose mediolateral at 60 degrees, never midline
- Discuss with patient beforehand as part of birth preparation 1
- Use restrictively: Only when clinical benefit outweighs risks, not routinely
The evidence unequivocally favors mediolateral over midline episiotomy when this intervention is deemed necessary, with the strongest protective effect against life-altering anal sphincter injuries in nulliparous women undergoing assisted vaginal delivery.