What movement does the sacrum undergo during delivery to help push the baby out?

• A. From extension to flexion-nutation
• B. From flexion to extension
• C. No movement
• D. Lateral rotation

Answer: (A)

During delivery, the sacrum moves by nutation, an anterior tilt of the sacral base that opens the pelvic outlet in the front-to-back direction and helps the baby descend. As labor progresses and the fetal head presses against the sacrum and ilia, the sacrum shifts from a more extended position toward nutation—so it goes from extension to flexion-nutation. This anterior tilt increases the anteroposterior diameter of the pelvis, aiding birth. Lateral rotation is not the primary movement driving this process, and a lack of movement would not facilitate delivery.