If a pregnant woman is hyperthyroid due to Graves’ disease or nodules, the woman should begin hyperthyroidism treatment right away. Typically, pregnant women receive antithyroid drug treatment (if newly diagnosed), or, if a woman is an existing patient, her dosage will be adjusted so that free T4 levels remain in the normal range for someone who is not pregnant.
The antithyroid drug of choice (especially during the first trimester) is propylthiouracil, because methimazole has a slightly higher (though very small) risk of birth defects. The Guidelines recommend switching to methimazole for the second and third trimesters.
If a woman has a severe negative reaction to antithyroid drugs, requires very high doses to control her hyperthyroidism, or has uncontrolled hyperthyroidism despite treatment, surgery may be recommended. The surgery would usually be recommended during the second trimester, when it is least likely to endanger the pregnancy.
Radioactive iodine should never be given to any woman who is or who might be pregnant.