Antenatal care: invasive prenatal diagnosis: 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 · Antenatal care: invasive prenatal diagnosis

Sample item

Which statement about chorionic villus sampling (CVS) is correct?

AIt is performed at 20 to 24 weeksBIt cannot be used for DNA analysisCIt is the test of choice for neural tube defectsDIt is usually performed at 10 to 13 weeks and allows early karyotyping

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

The answer and the reasoning

D. It is usually performed at 10 to 13 weeks and allows early karyotyping

CVS samples placental villi at 10 to 13 weeks, giving early karyotype or DNA results with a pregnancy loss risk of about 0.5 to 1 per cent. Amniocentesis is done at 15 to 18 weeks. Neural tube defects are detected by ultrasound and amniotic fluid AFP.

Option by option

A. It is performed at 20 to 24 weeks
At 20 to 24 weeks, amniocentesis or cordocentesis is used instead.
B. It cannot be used for DNA analysis
CVS tissue is excellent for DNA analysis of single-gene disorders.
C. It is the test of choice for neural tube defects
Neural tube defects are screened by AFP and ultrasound, not CVS.
D. It is usually performed at 10 to 13 weeks and allows early karyotyping (correct)
Correct. Early sampling is the main advantage of CVS.

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 D, It is usually performed at 10 to 13 weeks and allows early karyotyping. CVS samples placental villi at 10 to 13 weeks, giving early karyotype or DNA results with a pregnancy loss risk of about 0.

Why is "It is performed at 20 to 24 weeks" not the answer?

At 20 to 24 weeks, amniocentesis or cordocentesis is used instead.

Why is "It cannot be used for DNA analysis" not the answer?

CVS tissue is excellent for DNA analysis of single-gene disorders.

Why is "It is the test of choice for neural tube defects" not the answer?

Neural tube defects are screened by AFP and ultrasound, not CVS.

What concept does this question test?

It tests Antenatal care: invasive prenatal diagnosis in OBG. 5 to 1 per cent. Amniocentesis is done at 15 to 18 weeks. Neural tube defects are detected by ultrasound and amniotic fluid AFP.

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 Antenatal care: invasive prenatal diagnosis?

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.