A client with hypothyroidism asks the nurse if she will still need to take thyroid medication during the pregnancy. The nurse’s response is based on the knowledge that:
A. There is no need to take thyroid medication because the fetus’s thyroid produces a thyroid-stimulating hormone.
B. Regulation of thyroid medication is more difficult because the thyroid gland increases in size during pregnancy.
C. It is more difficult to maintain thyroid regulation during pregnancy due to a slowing of metabolism.
D. Fetal growth is arrested if thyroid medication is continued during pregnancy.
Correct Answer: B. Regulation of thyroid medication is more difficult because the thyroid gland increases in size during pregnancy.
During pregnancy, the thyroid gland triples in size. This makes it more difficult to regulate thyroid medication. During pregnancy, there are increased metabolic needs of the maternal body resulting in changes in thyroid physiology. These changes in thyroid physiology reflect in altered thyroid function tests.
Option A: There could be a need for thyroid medication during pregnancy. The serum TSH concentration is the initial and most reliable measure of thyroid function during pregnancy. As elaborated above, there are physiologic changes in TSH levels during pregnancy which warrants close monitoring of TSH levels. As per the latest American Thyroid Association (ATA) guidelines, serum TSH levels during pregnancy should be defined using population and trimester-specific based reference ranges.
Option C: The thyroid function does not slow. When population and trimester-specific normal ranges are not available, the ATA guidelines recommend reducing the lower limit of TSH by 0.4 mU/L and the upper limit by 0.5 mU/L. It would correspond to the TSH reference range of 0.1 to 4.0 mU/L during the first trimester with a gradual return of TSH towards the non-pregnant normal range during second and third trimesters.
Option D: Fetal growth is not arrested if thyroid medication is continued. There is an increase in iodine requirement during pregnancy due to an increase in maternal thyroid hormone production as well as an increase in renal iodine clearance. Along with the above two factors, there is also a fetal iodine requirement; therefore, dietary iodine requirements are higher during pregnancy.