What are the cardinal movements (mechanism) of normal labour?

1. Engagement and descent
2. Flexion (presents the smallest diameter)
3. Internal rotation (occiput rotates anteriorly)
4. Extension (the head delivers over the perineum)
5. Restitution (head realigns with the shoulders)
6. External rotation (shoulders rotate to the AP diameter)
7. Delivery of the shoulders and body

Clinical relevance. The cardinal movements are the framework for understanding normal delivery and where malpositions arise.

More Detail

Cardinal movements of labour

The mechanism of normal labour is the series of passive movements the fetus makes through the birth canal.

The movements

1. Engagement / descent - the widest diameter passes the pelvic inlet; descent continues throughout.
2. Flexion - the head flexes to present the smallest (suboccipitobregmatic) diameter.
3. Internal rotation - the occiput rotates anteriorly to fit the pelvic outlet.
4. Extension - the flexed head extends to deliver over the perineum (crowning).
5. Restitution - the head realigns with the shoulders.
6. External rotation - the shoulders rotate into the AP diameter of the outlet.
7. Delivery of the shoulders (anterior then posterior) and the body.

Significance

Failure of a movement causes a malposition/malpresentation (e.g. failed flexion -> brow/face; failed internal rotation -> occipitoposterior/deep transverse arrest).