Normal pregnancy and antenatal care: trisomy 18 serum screening: 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: trisomy 18 serum screening

Sample item

A 36-year-old woman at 16 weeks has a second-trimester screen showing low alpha-fetoprotein, low unconjugated oestriol, low total hCG and low inhibin A. Which fetal condition does this pattern most strongly suggest?

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

The answer and the reasoning

D. Trisomy 18

In trisomy 18 all the quadruple-test analytes tend to be low. In trisomy 21, hCG and inhibin A are raised while AFP and oestriol are low. Open neural tube and abdominal wall defects raise maternal serum AFP.

Option by option

  • A. Open neural tube defect

    An open neural tube defect raises maternal serum AFP rather than lowering it.

  • B. Fetal gastroschisis

    Gastroschisis leaks fetal protein into the amniotic fluid and raises maternal AFP.

  • C. Trisomy 21

    Trisomy 21 gives low AFP and oestriol but raised hCG and inhibin A.

  • D. Trisomy 18 (correct)

    Correct. A uniformly low pattern of AFP, oestriol, hCG and inhibin A characterises trisomy 18.

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 D, Trisomy 18. In trisomy 18 all the quadruple-test analytes tend to be low.

Why is "Open neural tube defect" not the answer?

An open neural tube defect raises maternal serum AFP rather than lowering it.

Why is "Fetal gastroschisis" not the answer?

Gastroschisis leaks fetal protein into the amniotic fluid and raises maternal AFP.

Why is "Trisomy 21" not the answer?

Trisomy 21 gives low AFP and oestriol but raised hCG and inhibin A.

What concept does this question test?

It tests Normal pregnancy and antenatal care: trisomy 18 serum screening in OBG. In trisomy 21, hCG and inhibin A are raised while AFP and oestriol are low. Open neural tube and abdominal wall defects raise maternal serum 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 Normal pregnancy and antenatal care: trisomy 18 serum screening?

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.