SBA — Single Best Answer · Review
Question 515
Endocrinology → General
Classification
Question
SSBAQuestion Header
A euthyroid woman is assessed during pregnancy after the oestrogen-associated rise in thyroxine-binding globulin. Which thyroid hormone pattern is expected?
Question Stem
Select the single best answer.
Options
A
Reduced total T4 and T3 with markedly increased free hormone concentrations
B
Reduced total and free T4 with complete suppression of TSH
C
Unchanged total T4 and T3 with markedly increased free T4
D
Reduced total T4 and T3 with unchanged thyroxine-binding globulin
E
Increased total T4 and T3 while free hormone concentrations remain essentially unchanged
Explanation
Oestrogen increases thyroxine-binding globulin during pregnancy. Consequently, total T4 and T3 concentrations increase, while free thyroid hormone concentrations remain essentially unchanged and the mother remains euthyroid. TSH is therefore the recommended assessment of thyroid status in pregnancy.
Option Validity
A) Total thyroid hormone concentrations increase rather than decrease as thyroxine-binding globulin rises.
B) The physiological rise in thyroxine-binding globulin does not produce reduced total and free T4 with complete TSH suppression in a euthyroid pregnancy.
C) Total T4 and T3 increase as thyroxine-binding globulin increases.
D) Pregnancy markedly increases thyroxine-binding globulin, producing increased rather than reduced total thyroid hormone concentrations.
Further Reading
Saxena, MRCOG-1 Basic Sciences, Endocrinology: Thyroid Function in Pregnancy.