External Rotation (Restitution)
After extension of the fetal vertex anteriorly (the fifth cardinal movement), the next step is external rotation, also known as restitution, where the occiput rotates to a transverse position to realign with the fetal shoulders.
Understanding the Seven Cardinal Movements
The question describes the first five cardinal movements in sequence:
- Engagement - the greatest transverse diameter (biparietal diameter) passes through the pelvic inlet
- Descent - the fetal head descends into the pelvis
- Flexion - the fetal chin is brought into close contact with the thorax
- Internal rotation - turning of the occiput toward the 12 o'clock (anterior) position
- Extension - uterine contractions extend the fetal vertex anteriorly, allowing the head to be delivered under the pubic symphysis
The Sixth Cardinal Movement: External Rotation (Restitution)
After the head is delivered through extension, the fetal head spontaneously rotates approximately 45 degrees back to realign with the shoulders, which remain in an oblique or transverse diameter of the pelvis. This movement is called restitution or external rotation 1.
- The occiput rotates from the anterior (12 o'clock) position back toward a transverse position (either 3 o'clock or 9 o'clock, depending on which side the fetal back is positioned) 1
- This rotation occurs because during internal rotation, the head rotated independently while the shoulders remained transverse; now the head realigns with the body 2, 1
- This is a passive movement that occurs naturally as the delivered head "untwists" from its rotated position
Clinical Significance
- External rotation is visible externally and confirms that the shoulders are preparing to deliver 1
- The direction of external rotation indicates which shoulder (anterior vs posterior) will deliver first
- After external rotation completes, the seventh and final cardinal movement (expulsion) occurs with delivery of the anterior shoulder, then posterior shoulder, followed by the rest of the body
Answer to the Question
The correct answer is (a) Rotation of occiput to transverse position - this describes external rotation/restitution, the sixth cardinal movement that follows extension of the fetal vertex.