Criteria for ROP (long rotation):
Attitude-head is deflexed
Position - Right occipito posterior
Presenting part: middle or anterior area of the left (right- in case of LOP) parietal bone
· The head engages through the right oblique diameter (ie.,Occipitofrontal diameter) in R.O.P and left oblique diameter in L.O.P.
· The engaging transverse diameter of the head is bi parietal (9.5cm) and that of antero-posterior diameter is either suboccipito frontal ( 10 cm ) or occipito frontal (11.5 cm ) Because of deflexion, engagement is delayed.
· The engaging antero posterior diameter lies in the oblique diameter of the pelvic brim.
· The occiput points to the right sacroiliac joint and sinciput to the left iliopectineal eminence.
Flexion: Descent takes place with increasing flexion. The occiput becomes the leading part.
Internal rotation of the head: The occiput reaches the pelvic floor first and rotates forward 3/8th of a circle along the right side of the pelvis to lie under the symphysis pubis. The shoulders follow, turning 2/ 8 th of a circle to from the left to the right oblique diameter.
Crowning: The occiput escapes under the symphysis pubis and the head is crowned
Extension: The sinciput, face and chin sweeps the perineum and the head is born by a movement of extension
Restitution: takes place and occiput turns 1/ 8 th of a circle to the right and now the head is in alignment with the shoulders.
Internal rotation of the shoulders and external rotation of the head :
The shoulders enter into the pelvis in the right oblique diameter, the anterior shoulder reaches the pelvic floor first and rotates forward 1/ 8th of a circle to lie under the symphysis pubis.
Lateral flexion: The anterior shoulder escapes under the symphysis pubis, the posterior shoulder sweeps the perineum and the rest of the body is born by a movement of lateral flexion.
Some cirumstances, the occiput fails to rotate and causes incomplete toward rotation- deep transverse arrest.
Non rotation- oblique posterior arrest
Malrotation- occipito-sacral arrest.