At operative birth, mediolateral episiotomy tracked with fewer sphincter injuries and midline with more

Design

Secondary analysis of a prospective multicentre cohort (MFMU APEX)

Population

5,277 term singleton operative vaginal deliveries in the US

Primary outcome

Third- or fourth-degree perineal laceration

Effect

Any episiotomy aOR 1.45 (95% CI 1.25 to 1.67); OASI incidence 20.1%

A secondary analysis of the US APEX cohort in Obstetrics and Gynecology (10 September 2026) looked at 5,277 term operative vaginal deliveries: 3,453 by vacuum and 1,824 by forceps. About a third had an episiotomy, most of them midline (1,301) rather than mediolateral (384). One in five women, 20.1%, sustained an obstetric anal sphincter injury.

Taken as a whole, episiotomy was associated with higher odds of sphincter injury (adjusted odds ratio 1.45, 95% CI 1.25 to 1.67). That average hid opposite effects. Midline episiotomy during vacuum delivery was associated with more injury, whether or not the woman had given birth vaginally before. Mediolateral episiotomy was associated with less injury in women without a previous vaginal birth, for both vacuum and forceps.

The design is observational, and operators choose an episiotomy for reasons the model may not capture. But the pattern matches earlier studies from settings with very different episiotomy habits. For a clinician deciding at the perineum, it argues against the midline cut at assisted birth and for considering a mediolateral cut in a first-time mother.

• Think twice about a midline episiotomy at vacuum delivery; it was linked to more sphincter injury at any parity.
• Consider a mediolateral episiotomy before an instrumental birth in a woman with no previous vaginal birth.
• Angle the mediolateral cut well away from the midline; a cut too close to vertical behaves like a midline one.
• Record the episiotomy type and angle in the delivery note.
• Audit your unit's episiotomy type and sphincter injury rate by instrument.

Why it matters

Asking whether to cut is the wrong question; the direction of the cut is what tracked with sphincter injury.

Don't overread it

This was an observational analysis, so it cannot prove that a mediolateral cut prevents injury in an individual woman.

The statistics, in plain English

An adjusted odds ratio of 1.45 means the odds of sphincter injury were about 45% higher with any episiotomy after accounting for second-stage length, age, BMI and birth weight. The interaction tests show that this average differs by type of cut, instrument and parity, so the overall figure is less useful than the subgroup pattern, although subgroup results are always less certain than a single headline.

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