Thyroid testing during pregnancy should be performed on symptomatic women or those with a personal history of
thyroid disease. Overt
hypothyroidism complicates up to 3 of 1,000 pregnancies and is characterized by nonspecific signs or symptoms that are easily confused with complaints common to pregnancy itself. Physiologic changes in serum
thyroid-stimulating hormone (TSH) and free
thyroxine (T(4)) related to pregnancy also confound the diagnosis of
hypothyroidism during pregnancy. If the TSH is abnormal, then evaluation of free T(4) is recommended. The diagnosis of overt
hypothyroidism is established by an elevated TSH and a low free T(4). The goal of treatment with
levothyroxine is to return TSH to the normal range. Overt
hyperthyroidism complicates approximately 2 of 1,000 pregnancies. Clinical features of
hyperthyroidism can also be confused with those typical of pregnancy. Clinical
hyperthyroidism is confirmed by a low TSH and elevation in free T(4) concentration. The goal of treatment with
thioamide drugs is to maintain free T(4) in the upper normal range using the lowest possible dosage.
Postpartum thyroiditis requiring
thyroxine replacement has been reported in 2% to 5% of women. Most women will return to the euthyroid state within 12 months.