ATA Guidelines Tools

11 Î New Pregnancy a. In a newly-pregnant woman with Graves' disease, who is euthyroid on a low dose of MMI (≤5–10 mg/day) or PTU (≤100–200 mg/day), the physician should consider discontinuing all antithyroid medication given potential teratogenic effects. The decision to stop medication should take into account the disease history, goiter size, duration of therapy, results of recent thyroid function tests, TRAb measurement, and other clinical factors. (W-L) b. Following cessation of antithyroid medication, maternal thyroid function testing (TSH, and FT4 or total T4 [TT4]) and clinical examination should be performed every 1–2 weeks to assess maternal and fetal thyroid status. If the pregnant woman remains clinically and biochemically euthyroid, test intervals may be extended to 2-4 weeks during the 2 nd and 3 rd trimester. (W-L) c. At each assessment, the decision to continue conservative management (withholding antithyroid medication) should be guided both by the clinical and the biochemical assessment of maternal thyroid status. (W-L) Î High Risk • In pregnant women with a high risk of developing thyrotoxicosis if antithyroid drugs were to be discontinued, continued antithyroid medication may be necessary. Factors predicting high clinical risk include being currently hyperthyroid, or requirement of 5–10 mg/day MMI or 100–200 mg/day PTU to maintain a euthyroid state. In such cases: • PTU is recommended for the treatment of maternal hyperthyroidism through 16 weeks of pregnancy. (S-M) • Pregnant women receiving MMI who are in need of continuing therapy during pregnancy should be switched to PTU as early as possible. (W-L) • When shifting from MMI to PTU, a dose ratio of approximately 1:20 should be used (e.g. MMI 5 mg daily = PTU 100 mg twice daily). (S-M) • If ATD therapy is required after 16 weeks gestation, it remains unclear whether PTU should be continued or therapy changed to MMI. Since both medications are associated with potential adverse effects and shifting potentially may lead to a period of less-tight control, no recommendation regarding switching antithyroid drug medication can be made at this time. (I) Î Antithyroid Drugs • In women being treated with antithyroid drugs in pregnancy, FT4/TT4 and TSH should be monitored approximately every 4 weeks. (S-M) • Antithyroid medication during pregnancy should be administered at the lowest effective dose of MMI or PTU, targeting maternal serum FT4/TT4 at or moderately above the reference range. (S-H) Î A combination regimen of LT4 and an antithyroid drug should NOT be used in pregnancy, except in the rare situation of isolated fetal hyperthyroidism. (S-H)

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