Crowning, extension and restitution of the foetal head
After crowning (the head stretching the muscle and skin at the vaginal opening), the head extends to be born, then restitutes, turning to realign with the shoulders.
Remember
Once the head is born it untwists to line up with the shoulders (restitution, seen as external rotation), and that lets the shoulders be delivered.
In a normal head-first delivery, the baby moves through the pelvis in a fixed sequence. The early movements include flexion (tucking the chin towards the chest) and internal rotation (the head turning inside the pelvis to fit its shape). Next comes crowning: the head stretches the perineum, the skin and muscle that lie between the vagina and the anus, and becomes visible at the vaginal opening.
After crowning, the head is delivered by extension. It tilts back as it emerges. The shoulders are still inside the pelvis and lie at an angle to the head, so the head now turns to line up with them. This is restitution, a word that means restoring, because the head swings back to line up with the shoulders. It is seen as the head turning to one side once it is born, and it is also called external rotation.
Once the head is realigned, the shoulders lie front to back (anteroposterior) in the pelvic outlet, the lower opening of the pelvis. From there they can be delivered. The anterior shoulder comes first, then the posterior shoulder, and the rest of the body follows rapidly.
The turn of the head is also a useful bedside sign. If the head is born but does not turn, the failure of restitution can be a sign of shoulder dystocia, a delay in delivering the shoulders in which the anterior shoulder may be stuck behind the pubic symphysis (the joint at the front of the pelvis).
Key facts
- Crowning
- the head stretches the perineum and is visible at the vaginal opening.
- Extension
- after crowning the head tilts back and is born.
- Restitution
- the born head turns to realign with the shoulders, and this is seen as external rotation.
- Sequence from flexion
- flexion, internal rotation, crowning, extension, restitution, then rotation and delivery of the shoulders, then the rest of the body.
- The shoulders
- after restitution they lie front to back, and the anterior shoulder is delivered before the posterior shoulder.
- Failure of restitution
- can be a sign of shoulder dystocia.
Exam traps
- Turning the occiput (the back of the head) forwards is internal rotation, which comes before the head is born. The turn that follows birth of the head is restitution and lines the head up with the shoulders.
- Restitution does not come before extension. The head extends first and then turns, and the shoulders are not delivered by further extension of the head.
- Flexion (tucking the chin towards the chest) does not follow crowning, because it is an early movement that happens before the head turns and crowns.
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