This issue highlights Endocrine Board Review. Test your clinical knowledge and prepare for your exam. Available on the online store.
A 27-year-old woman with a 10-year history of Hashimoto hypothyroidism has been trying to become pregnant and is now 1 week late for her menses. A home pregnancy kit had a positive result. Thyroid function tests 1 month ago documented a serum TSH value of 1.2 mIU/L. Her primary care physician requests your management advice.
Which of the following recommendations is most appropriate?
- Decrease levothyroxine to achieve a target TSH concentration of 2.5 mIU/L
- Continue the current levothyroxine dosage
- Increase levothyroxine by 30%
- Increase levothyroxine by 40%
- Increase levothyroxine by 50%
Answer: C) Increase levothyroxine by 30%
Most thyroid hormone–treated women need to increase their levothyroxine dosage during pregnancy to maintain normal serum TSH values. The absolute increase required depends in part on the underlying etiology of the hypothyroidism, as well as on the preconception serum TSH level. A randomized trial has demonstrated that euthyroid women receiving once-daily dosing of levothyroxine (regardless of the dose) who took 9 tablets per week instead of 7 tablets per week (a 29% increase) starting early in gestation were able to maintain euthyroidism in the first trimester. Current recommendations are to increase thyroid hormone doses empirically by 25% to 30% as soon as pregnancy is confirmed, with close follow-up of serum TSH levels through midgestation.
The remaining answer options either fail to recognize the rapid increase in thyroid hormone requirements in most women during early pregnancy (Answers A and B) or overreact by recommending a potentially excessive increase in the levothyroxine dosage (Answers D and E).
Recommend that hypothyroid women who become pregnant promptly increase their levothyroxine dosage by approximately 30%.
Yassa L, Marqusee E, Fawcett R, Alexander EK. Thyroid hormone early adjustment in pregnancy (the THERAPY) trial. J Clin Endocrinol Metab. 2010;95(7):3234-3241.
Alexander EK, Marqusee E, Lawrence J, Jarolim P, Fischer GA, Larsen PR. Timing and magnitude of increases in levothyroxine requirements during pregnancy in women with hypothyroidism. N Engl J Med. 2004;351(3):241-249.
Stagnaro-Green A, Abalovich M, Alexander E, et al; American Thyroid Association Taskforce on Thyroid Disease During Pregnancy and Postpartum. Guidelines of the American Thyroid Association for the diagnosis and management of thyroid disease during pregnancy and postpartum. Thyroid. 2011;21(10):1081-1125.