Normal pregnancy and antenatal care: thyroid binding in 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 · Normal pregnancy and antenatal care: thyroid binding in pregnancy

Sample item

A healthy pregnant woman at 16 weeks has a total T4 above the usual adult range, with normal TSH and normal free T4. What explains this?

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

The answer and the reasoning

B. Oestrogen-induced rise in thyroxine-binding globulin

Oestrogen raises hepatic production of thyroxine-binding globulin, so total T4 and T3 rise while the free hormones remain normal. Pregnant women are therefore assessed by TSH and free T4, not total T4. TSH may fall slightly in the first trimester because of hCG.

Option by option

  • A. Subclinical hyperthyroidism

    Subclinical hyperthyroidism would show a low TSH with normal free T4 beyond the first trimester.

  • B. Oestrogen-induced rise in thyroxine-binding globulin (correct)

    Correct. More binding protein raises the total hormone without changing free levels.

  • C. Increased peripheral conversion of T4 to T3

    Increased conversion would affect T3 and would not account for a raised total T4 with normal TSH.

  • D. Autoimmune thyroiditis

    Autoimmune thyroiditis would alter the TSH and free T4 and is not the explanation for a high total T4 alone.

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 B, Oestrogen-induced rise in thyroxine-binding globulin. Oestrogen raises hepatic production of thyroxine-binding globulin, so total T4 and T3 rise while the free hormones remain normal.

Why is "Subclinical hyperthyroidism" not the answer?

Subclinical hyperthyroidism would show a low TSH with normal free T4 beyond the first trimester.

Why is "Increased peripheral conversion of T4 to T3" not the answer?

Increased conversion would affect T3 and would not account for a raised total T4 with normal TSH.

Why is "Autoimmune thyroiditis" not the answer?

Autoimmune thyroiditis would alter the TSH and free T4 and is not the explanation for a high total T4 alone.

What concept does this question test?

It tests Normal pregnancy and antenatal care: thyroid binding in pregnancy in OBG. Pregnant women are therefore assessed by TSH and free T4, not total T4. TSH may fall slightly in the first trimester because of hCG.

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: thyroid binding in 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.