Normal pregnancy and antenatal care: early chorionic villus sampling: 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 · Normal pregnancy and antenatal care: early chorionic villus sampling

Sample item

A woman at 8 weeks undergoes chorionic villus sampling for prenatal diagnosis. Why is the procedure normally postponed until 10 to 13 weeks?

AVilli cannot be obtained before 10 weeks of gestationBA fetal karyotype cannot be read before 10 weeksCEarlier sampling risks limb reduction defectsDEarlier sampling causes neural tube defects in the fetus

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

The answer and the reasoning

C. Earlier sampling risks limb reduction defects

Chorionic villus sampling before about 9 to 10 weeks has been associated with transverse limb reduction defects and oromandibular hypogenesis, probably due to vascular disruption. The standard window is therefore 10 to 13 weeks.

Option by option

A. Villi cannot be obtained before 10 weeks of gestation
Villi can technically be obtained earlier, but the procedure is avoided because of the risk to the fetus.
B. A fetal karyotype cannot be read before 10 weeks
Karyotyping of villus cells is possible earlier; the issue is fetal injury.
C. Earlier sampling risks limb reduction defects (correct)
Correct. Very early sampling is associated with limb reduction defects.
D. Earlier sampling causes neural tube defects in the fetus
Neural tube defects are not caused by sampling, because the neural tube has already closed by then.

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.

Questions about this OBG question

What is the answer to this OBG question?

The best answer is C, Earlier sampling risks limb reduction defects. Chorionic villus sampling before about 9 to 10 weeks has been associated with transverse limb reduction defects and oromandibular hypogenesis, probably due to vascular disruption.

Why is "Villi cannot be obtained before 10 weeks of gestation" not the answer?

Villi can technically be obtained earlier, but the procedure is avoided because of the risk to the fetus.

Why is "A fetal karyotype cannot be read before 10 weeks" not the answer?

Karyotyping of villus cells is possible earlier; the issue is fetal injury.

Why is "Earlier sampling causes neural tube defects in the fetus" not the answer?

Neural tube defects are not caused by sampling, because the neural tube has already closed by then.

What concept does this question test?

It tests Normal pregnancy and antenatal care: early chorionic villus sampling in OBG. The standard window is therefore 10 to 13 weeks.

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 Normal pregnancy and antenatal care: early chorionic villus sampling?

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.