Medical genetics: cell-free DNA screening: practice question

A Anatomy 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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Anatomy · Medical genetics: cell-free DNA screening

Sample item

A pregnant woman at 12 weeks has a high-risk result for trisomy 21 on cell-free DNA testing. What is the best next step?

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

The answer and the reasoning

B. Invasive diagnostic testing with CVS or amniocentesis

Cell-free DNA testing derived from the placenta is a very sensitive screening test but not diagnostic, as placental mosaicism can give false positives. A positive result should be confirmed by karyotype or microarray on villi or amniotic fluid before any decision.

Option by option

  • A. Repeat cell-free DNA testing after 4 weeks

    Repeating the same screen does not give a diagnosis.

  • B. Invasive diagnostic testing with CVS or amniocentesis (correct)

    Correct. A screening result must be confirmed by a diagnostic invasive test.

  • C. Quadruple test at 16 weeks

    The quadruple test is a less sensitive screen and cannot confirm trisomy.

  • D. Detailed ultrasound alone

    Ultrasound can show soft markers but cannot confirm trisomy 21.

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 Anatomy question

What is the answer to this Anatomy question?

The best answer is B, Invasive diagnostic testing with CVS or amniocentesis. Cell-free DNA testing derived from the placenta is a very sensitive screening test but not diagnostic, as placental mosaicism can give false positives.

Why is "Repeat cell-free DNA testing after 4 weeks" not the answer?

Repeating the same screen does not give a diagnosis.

Why is "Quadruple test at 16 weeks" not the answer?

The quadruple test is a less sensitive screen and cannot confirm trisomy.

Why is "Detailed ultrasound alone" not the answer?

Ultrasound can show soft markers but cannot confirm trisomy 21.

What concept does this question test?

It tests Medical genetics: cell-free DNA screening in Anatomy. A positive result should be confirmed by karyotype or microarray on villi or amniotic fluid before any decision.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Medical genetics: cell-free DNA screening?

Learn every nerve by its route, its muscles and what a lesion looks like at the bedside. That one habit answers a large share of questions. Then use the flashcards and the other Anatomy 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.