Reproduction: fetoplacental unit: practice question

A Physiology 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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Physiology · Reproduction: fetoplacental unit

Sample item

In a pregnancy with fetal anencephaly, maternal urinary oestriol is very low although the placenta is otherwise normal. What is the most likely mechanism?

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

The answer and the reasoning

B. The small fetal adrenal produces little DHEA sulphate, which the fetal liver and placenta normally convert to oestriol

Oestriol is the main oestrogen of late pregnancy and needs both fetus and placenta. The fetal adrenal makes DHEA sulphate under fetal ACTH, the fetal liver hydroxylates it at C16, and the placenta aromatises it to oestriol. Anencephaly removes fetal pituitary ACTH drive, the fetal adrenal atrophies and oestriol falls.

Option by option

  • A. The maternal corpus luteum has failed, so no oestriol is available

    The corpus luteum is relevant to early pregnancy and not to late oestriol production.

  • B. The small fetal adrenal produces little DHEA sulphate, which the fetal liver and placenta normally convert to oestriol (correct)

    Correct. The fetal adrenal supplies the precursor for the placenta.

  • C. The placenta fails to secrete hCG, which is needed for the oestriol precursor

    hCG maintains the corpus luteum early on and is not a precursor of oestriol.

  • D. The placenta cannot make progesterone and so cannot produce oestriol

    The placenta does make progesterone, and the defect here is in precursor supply.

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 Physiology question

What is the answer to this Physiology question?

The best answer is B, The small fetal adrenal produces little DHEA sulphate, which the fetal liver and placenta normally convert to oestriol. Oestriol is the main oestrogen of late pregnancy and needs both fetus and placenta.

Why is "The maternal corpus luteum has failed, so no oestriol is available" not the answer?

The corpus luteum is relevant to early pregnancy and not to late oestriol production.

Why is "The placenta fails to secrete hCG, which is needed for the oestriol p…" not the answer?

hCG maintains the corpus luteum early on and is not a precursor of oestriol.

Why is "The placenta cannot make progesterone and so cannot produce oestriol" not the answer?

The placenta does make progesterone, and the defect here is in precursor supply.

What concept does this question test?

It tests Reproduction: fetoplacental unit in Physiology. The fetal adrenal makes DHEA sulphate under fetal ACTH, the fetal liver hydroxylates it at C16, and the placenta aromatises it to oestriol. Anencephaly removes fetal pituitary ACTH drive, the fetal adrenal atrophies and oestriol falls.

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 Reproduction: fetoplacental unit?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.