Mechanism of labour

Series of changes in position and attitude that the fetus undergoes to accommodate itself to and through the maternal pelvis.

Flexion

Brings smallest diameter into engagement.Posterior fontanelle being lower than anterior fontanelle.

Internal rotation 

Presenting part reaches sloping pelvic floor causing lowest point (occiput) to rotate forward

Extension

Further descent occurs and the head extends to get through the perineum.

Restitution and external rotation.

Because the shoulders at the point of the head being delivered are only just reaching the pelvic floor they are often still negotiating the pelvic outlet and the fetus may naturally align its head with the shoulders. This is called restitution and visually you may see the head externally rotate to face the right or left medial thigh of the mother.

Watch the video below: