Normal pregnancy and antenatal care: amniotic fluid AFP and acetylcholinesterase: 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: amniotic fluid AFP and acetylcholinesterase

Sample item

At 17 weeks, maternal serum AFP is 3.2 MoM. Amniocentesis shows raised amniotic fluid AFP, and gel electrophoresis shows an acetylcholinesterase band. What does this combination best indicate?

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

The answer and the reasoning

B. Open neural tube defect

Raised AFP together with a positive acetylcholinesterase band is the biochemical pattern of an open neural tube defect or an abdominal wall defect. Errors of dating raise AFP only in the serum and do not produce a positive band. Trisomies 21 and 18 are associated with low maternal AFP.

Option by option

  • A. Trisomy 21

    Trisomy 21 is associated with a low maternal serum AFP.

  • B. Open neural tube defect (correct)

    Correct. Leakage of fetal proteins into the liquor through an open defect raises both markers.

  • C. Trisomy 18

    Trisomy 18 gives low AFP together with low hCG and low oestriol.

  • D. Underestimated gestational age

    Wrong dating can change the MoM but does not cause a positive acetylcholinesterase band.

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 OBG question

What is the answer to this OBG question?

The best answer is B, Open neural tube defect. Raised AFP together with a positive acetylcholinesterase band is the biochemical pattern of an open neural tube defect or an abdominal wall defect.

Why is "Trisomy 21" not the answer?

Trisomy 21 is associated with a low maternal serum AFP.

Why is "Trisomy 18" not the answer?

Trisomy 18 gives low AFP together with low hCG and low oestriol.

Why is "Underestimated gestational age" not the answer?

Wrong dating can change the MoM but does not cause a positive acetylcholinesterase band.

What concept does this question test?

It tests Normal pregnancy and antenatal care: amniotic fluid AFP and acetylcholinesterase in OBG. Errors of dating raise AFP only in the serum and do not produce a positive band. Trisomies 21 and 18 are associated with low maternal AFP.

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 Normal pregnancy and antenatal care: amniotic fluid AFP and acetylcholinesterase?

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.