In a persistent occiput posterior (OP) position at full dilatation, the MOST common mechanism by which spontaneous rotation to occiput anterior (OA) occurs is:

• A Short rotation of 45° directly to the anterior position
• B Asynclitism followed by direct OP delivery without rotation
• C Passive rotation during late first stage by uterine contractions
• D Long rotation of 135° through the posterior, transverse, and anterior positions ✓

Explanation

In persistent OP, the fetal head must rotate 135° from the posterior position, sweeping through the transverse position (direct OP → ROT/LOT → OA) — this is the 'long rotation'. Alternatively, a 'short rotation' of 45° produces face-to-pubis (direct OP) delivery, which is less common. Most spontaneous rotations are the long arc. Asynclitism alone does not rotate the head; rotation occurs primarily in the second stage.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.