Labour Room Emergency: Shoulder Dystocia, Episiotomy & the Anatomy You Actually Need to Know

Estimated reading time: 5 minutes

When things get tense in the labour room, clear anatomy and calm technique matter more than anything else. This blog is focusing on episiotomy — the why, the how, and the bits of anatomy that decide whether a patient walks out better or worse. No big textbook lecture here — just practical, clinically useful points I always stress on rounds.

The superficial perineal compartment — what’s really there

If you picture the perineum, think of two compartments: superficial and deep. For episiotomy, we mostly care about the superficial layer. It contains:

• An erectile body that continues into the clitoris (homologue of the penis),
  
• A few important muscles, and
  
• The Bartholin (vestibular) glands.

The key muscles you’ll notice on the surface are:

• Ischiocavernosus (runs along the ischium) — not that relevant for episiotomy,
  
• Bulbocavernosus — very important, and
  
• Superficial transverse perineal — also important.

Deeper down, you’ll find fibres of the pubococcygeus. All these muscles meet at a common point—the perineal body—and that little structure is hugely important.

Click Here to Watch: Labor Room Emergency! 👶 Shoulder Dystocia & Episiotomy Explained

Why the perineal body matters?

The perineal body is the anchor for all those muscles. With repeated stretching during vaginal births or poorly healed tears, the body becomes lax. The consequence? Early pelvic organ prolapse and pelvic floor dysfunction.

I always ask postpartum patients if they’ve been taught pelvic floor (Kegel) exercises. Too often, the answer is no. If the perineal body is thin on exam (you can check the posterior fourchette), reconstruction should be considered.

So, what is an episiotomy?

Simply put, an episiotomy is an intentional perineal incision made to enlarge the vaginal outlet during delivery. It’s iatrogenic — we do it for a reason. Usually it’s performed with episiotomy scissors, but in an emergency, a stout Mayo scissor will do.

Technically, an episiotomy corresponds to around a grade 1–2 tear (Sultan’s classification), but incorrect angle or timing can create extensions and worse grades.

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When should you cut?

The right time is during crowning — when the fetal head has thinned the perineum and is visible between the labia. If you cut too early, the tissue is thick, and you risk deeper muscle injury. If you wait until crowning, you can often make a neat, thin incision and avoid uncontrolled tearing.

Angle matters — and here’s the simple math

This is the practical bit I drill into trainees:

• If you cut at about 40° from the midline while the perineum is stretched, that angle shortens as tissue recoils after delivery and becomes dangerously close to the anal sphincter, making extension into the anal mucosa possible.
  
• Aim for 60° from the midline. After recoil, this generally becomes about 45°, which safely bypasses the anal canal.

Measure the angle from the midline (a line joining the posterior fourchette to the anal opening), not from a horizontal line. Specially designed episiotomy scissors help maintain this angle.

Types of episiotomy — and when to use which

There are several kinds; keep it simple:

1. Median (midline)
   
   • Cut along the midline (±25°). Once popular, now less favoured because extensions can track straight to the anal mucosa → grade 3–4 tears.
     
2. Modified median
   
   • Midline start, slight lateral extension (~2.5 cm each side). Gives room but can injure deeper muscles and cause more bleeding and sitting pain.
     
3. J-shaped
   
   • Starts midline, then curves laterally. Useful if you want to avoid a straight midline extension.
     
4. Mediolateral (my preferred in most obstetric practice)
   
   • Taken at ~60° to the midline, either side (commonly maternal left if you’re right-handed). Safer from sphincter injury and the most commonly used.
     
5. Radical lateral / Schuchardt’s incision
   
   • Rare in obstetrics — used mainly in gynecologic surgery (e.g., to increase vaginal access in postmenopausal vagina).

Which muscles get cut?

With a proper mediolateral episiotom,y you’ll usually transect:

1. Superficial transverse perineal (most consistently),
   
2. Bulbocavernosus, and
   
3. Sometimes, a bit of pubococcygeus if the incision is deep or poorly placed.

If you follow the angle and timing recommendations, you minimise deeper damage.

A practical note on technique

• Hold the scissors so the blade points away from your body and aim for the 60° line.
  
• Prefer to cut during crowning so the incision is as small and controlled as needed.
  
• If you’re called for a repair, identify which muscles were cut and reapproximate them anatomically — it makes a huge difference in recovery.

A quick clinical aside — Dührssen’s incision

In rare scenarios where the cervix is obstructing delivery (e.g., entrapped cervix) a Dührssen’s incision at 2 or 10 o’clock is taught. The reason for those positions is to avoid the descending cervical branches (around 3 and 9 o’clock). Knowing vascular anatomy prevents uncontrolled bleeding.

Conclusion:

Episiotomy isn’t a “routine” reflex — it’s a surgical decision. If done at the right time, at the correct angle, and with careful repair, it prevents worse tears and promotes better pelvic floor outcomes. Sound anatomy + careful technique = fewer complications.

Want more practical, hands-on tips on perineal repair and pelvic floor preservation? I cover step-by-step repair techniques in my procedural sessions — they make the real difference at the bedside.