At an assisted birth, the type of episiotomy points in opposite directions

Design

secondary analysis of a prospective multicentre cohort, observational

Population

5,277 women with term, cephalic, singleton operative vaginal delivery in the United States

Primary outcome

obstetric anal sphincter injury (third- or fourth-degree tear)

Effect

injury in 20.1% (95% CI 19.0 to 21.2); episiotomy vs none adjusted OR 1.45 (95% CI 1.25 to 1.67), with opposite directions by episiotomy type

A secondary analysis of the MFMU APEX cohort looked at 5,277 term, cephalic, singleton operative vaginal deliveries in the United States — 3,453 vacuum and 1,824 forceps. Episiotomy was performed in 1,704 (32.3%), most of them midline. Obstetric anal sphincter injury occurred in 20.1% (95% CI 19.0 to 21.2), and as a single exposure episiotomy was associated with higher odds of injury after adjustment for second stage length, maternal age, body mass index and birth weight (adjusted odds ratio 1.45, 95% CI 1.25 to 1.67).

That headline number hides the finding that matters. Episiotomy type interacted significantly with both the type of assisted delivery (P<.001) and previous vaginal birth (P=.02). Midline episiotomy at vacuum delivery was associated with higher odds of sphincter injury whether or not the woman had delivered vaginally before. Mediolateral episiotomy was associated with lower odds in women without a previous vaginal delivery, for both vacuum and forceps.

In practice this argues against the reflex midline cut at a vacuum delivery, and gives a defensible reason to choose mediolateral when an episiotomy is judged necessary at a first vaginal birth. It does not tell you to cut. The comparison group here is no episiotomy, and for a multiparous woman the analysis offers no evidence that cutting helps at all.

• Decide type before the instrument goes on, not in the moment.
• For a first vaginal birth needing an episiotomy at assisted delivery, mediolateral is the defensible choice.
• Record the type, the angle and the indication — the type is what the evidence turns on.
• Note previous vaginal birth in the decision: the benefit signal sits only in those without one.
• Audit your unit's midline-to-mediolateral ratio at operative vaginal delivery; many units have never looked.

Why it matters

The choice between a midline and a mediolateral cut is usually local habit, and this says the two do not carry the same risk.

Don't overread it

This is observational — the clinician chose the episiotomy, and the judgement that prompted it may be the same thing that predicted the tear.

The statistics, in plain English

An adjusted odds ratio of 1.45 with a confidence interval of 1.25 to 1.67 means the interval sits well clear of 1.0, so the association with episiotomy overall is unlikely to be chance. The interaction P values are the important part: they say the effect of episiotomy is not the same across groups, which is why the combined figure is misleading on its own. Adjustment handles the confounders that were measured; it cannot handle the reason the clinician chose to cut, which is not in the dataset.

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