Full flexion of head reduced the advancing diameter of the head.
It is a continuous process.
Baby lies in Flexion.
Posterior parietal bone glides past the sacral promontory in anterior parietal
Maximum diameter of the head (biparietal diameter) stretches the vulval outlet without
any recession of the head even after the contraction is over.
Torsion of neck
Rotation of shoulders in the same direction to the extent of 1/8th of the circle.
Shoulders along oblique diameter.
Anterior rotation by 2/8th of a circle of the occiput, in occipito-lateral position. The
rotation will be 1/8th in oblique anterior position.
Occiput faces Pubic Symphysis.
Birth of shoulders and trunk
Posterior shoulder sweeps the perineum.
Trunk expelled in lateral flexion.
Rotation of the head through 1/8th of a circle in same direction as restitution.
Shoulders in antero-posterior diameter.
Rotating the head through 1/8th of a circle in direction opposite to the internal rotation.
The occiput points to the maternal thigh of the corresponding side to which it originally lay.
Release of the chin through the anterior margin of the stretched perineum, the head drops
down, bringing the chin in close proximity to the maternal anal opening.