Mechanism of labor: practice question

A OBG question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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OBG · Mechanism of labor

Sample item

What primarily drives the fetal head downward through the pelvic canal during labour?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Uterine contractions and maternal bearing-down effort, modified by pelvic and head dimensions

Descent is produced by uterine contractions, abdominal muscle effort in the second stage and the shape of the pelvic canal and fetal head. Gravity and ligament laxity have only minor roles.

Option by option

  • A. Gravity acting alone

    Gravity has minimal effect in a recumbent labouring woman.

  • B. Uterine contractions and maternal bearing-down effort, modified by pelvic and head dimensions (correct)

    Correct. Expulsive forces working against pelvic resistance move the fetus downward.

  • C. Relaxation of pelvic ligaments alone

    Ligament relaxation permits some mobility but does not generate force.

  • D. Maternal lumbar lordosis

    Lordosis changes the pelvic inclination but does not push the head.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this OBG question

What is the answer to this OBG question?

The best answer is B, Uterine contractions and maternal bearing-down effort, modified by pelvic and head dimensions. Descent is produced by uterine contractions, abdominal muscle effort in the second stage and the shape of the pelvic canal and fetal head.

Why is "Gravity acting alone" not the answer?

Gravity has minimal effect in a recumbent labouring woman.

Why is "Relaxation of pelvic ligaments alone" not the answer?

Ligament relaxation permits some mobility but does not generate force.

Why is "Maternal lumbar lordosis" not the answer?

Lordosis changes the pelvic inclination but does not push the head.

What concept does this question test?

It tests Mechanism of labor in OBG. Gravity and ligament laxity have only minor roles.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Mechanism of labor?

Learn management algorithms as steps: PPH, eclampsia, ectopic pregnancy. Then use the flashcards and the other OBG questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.