Complications of pregnancy: hook effect in molar pregnancy: 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 · Complications of pregnancy: hook effect in molar pregnancy

Sample item

A woman at 14 weeks has vaginal bleeding with grape-like vesicles, and a uterus larger than dates. A urine pregnancy test is negative, but serum hCG is above 1,000,000 IU/L. What explains the false-negative test?

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

The answer and the reasoning

D. The high-dose hook effect from antigen excess

Very high hCG saturates both antibodies in the immunoassay and prevents the sandwich from forming, producing a false-negative result. Diluting the sample reveals the true positive. It is seen in molar pregnancy and choriocarcinoma.

Option by option

  • A. Ectopic pregnancy

    An ectopic pregnancy would not raise hCG to this level.

  • B. Fetal death with falling hCG

    Fetal death would lower hCG, which is not seen here.

  • C. Expired test strip

    An expired strip is not a satisfactory explanation when serum hCG is this high and the history fits a mole.

  • D. The high-dose hook effect from antigen excess (correct)

    Correct. Antigen excess saturates the antibodies in the test.

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 D, The high-dose hook effect from antigen excess. Very high hCG saturates both antibodies in the immunoassay and prevents the sandwich from forming, producing a false-negative result.

Why is "Ectopic pregnancy" not the answer?

An ectopic pregnancy would not raise hCG to this level.

Why is "Fetal death with falling hCG" not the answer?

Fetal death would lower hCG, which is not seen here.

Why is "Expired test strip" not the answer?

An expired strip is not a satisfactory explanation when serum hCG is this high and the history fits a mole.

What concept does this question test?

It tests Complications of pregnancy: hook effect in molar pregnancy in OBG. Diluting the sample reveals the true positive. It is seen in molar pregnancy and choriocarcinoma.

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 Complications of pregnancy: hook effect in molar pregnancy?

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.