Labour: pelvic measurements: 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 · Labour: pelvic measurements

Sample item

If the diagonal conjugate measures 12 cm, the obstetric conjugate is approximately:

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

The answer and the reasoning

A. 10 to 10.5 cm

The diagonal conjugate is measured clinically from the sacral promontory to the lower border of the symphysis. The obstetric conjugate is about 1.5 to 2 cm less, so 12 cm gives 10 to 10.5 cm. A minimum of 10 cm is considered adequate.

Option by option

  • A. 10 to 10.5 cm (correct)

    Correct. Subtract 1.5 to 2 cm from the diagonal conjugate.

  • B. 12 cm

    This ignores the thickness of the symphysis.

  • C. 13.5 cm

    This adds rather than subtracts.

  • D. 8 cm

    This subtracts too much.

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.

More OBG questions

Questions about this OBG question

What is the answer to this OBG question?

The best answer is A, 10 to 10.5 cm. The diagonal conjugate is measured clinically from the sacral promontory to the lower border of the symphysis.

Why is "12 cm" not the answer?

This ignores the thickness of the symphysis.

Why is "13.5 cm" not the answer?

This adds rather than subtracts.

Why is "8 cm" not the answer?

This subtracts too much.

What concept does this question test?

It tests Labour: pelvic measurements in OBG. The obstetric conjugate is about 1.5 to 2 cm less, so 12 cm gives 10 to 10.5 cm. A minimum of 10 cm is considered adequate.

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 Labour: pelvic measurements?

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.