Question

The four cardinal movements, flexion, internal rotation, extension, and restitution with external rotation, constitute part of the normal mechanism of labor. The chronological order in which they occur is

• A. Flexion, internal rotation, extension, restitution and external rotation
• B. Internal rotation, flexion, extension, restitution and external rotation
• C. Flexion, extension, restitution and external rotation, internal rotation
• D. Internal rotation, extension, restitution and external rotation, flexion

Hint:

Walk through how the head has to turn and tilt as it moves down and out of the birth canal.

Answer 1

The Correct Option is A

Step 1: Recall the full list of cardinal movements of labor.
The normal mechanism of labor for a baby in the vertex position follows a set sequence, engagement, descent, flexion, internal rotation, extension, restitution and external rotation, and finally expulsion. Engagement, descent, and expulsion are not among the four movements listed in this question, so we focus on the middle four.

Step 2: Explain why flexion comes first among the four.
As the head descends and meets resistance from the pelvic floor and cervix, the chin tucks toward the chest. This flexion presents the smallest diameter of the head, the suboccipitobregmatic diameter, to the pelvis, making further descent easier.

Step 3: Explain why internal rotation comes next.
After flexion, the well flexed head reaches the level of the ischial spines and rotates so the occiput turns toward the front, or occasionally the back, aligning the head's longest diameter with the widest diameter of the pelvic outlet.

Step 4: Explain why extension follows.
Once the head is at the vulva, it extends as it passes under the pubic arch, since the birth canal now curves forward and the head must straighten out to be born.

Step 5: Explain why restitution and external rotation come last.
Once the head is delivered, it untwists back to its natural relationship with the shoulders (restitution) and then rotates further as the shoulders themselves rotate internally to pass through the pelvis (external rotation). This is the final step of the four before the shoulders and body are delivered.

Step 6: Confirm the order.
Putting these together gives flexion, then internal rotation, then extension, then restitution and external rotation, matching sequence 1, 2, 3, 4.

Final Answer:
The chronological order is flexion, internal rotation, extension, and restitution with external rotation.
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