NOTE
Methimazole is an FDA pregnancy category D so should not be used in the first trimester (it is
acceptable in the second and third). PTU has a risk of liver failure (rare) so should be used only
in the first trimester.Management. Antithyroid medications are the first line of therapy in
pregnancy, but they can cross the placentae leading to fetal hypothyroidism. PTU
and methimazole are thioamides that block thyroid hormone synthesis. Subtotal
thyroidectomy is primarily indicated when antithyroid medical therapy fails and
is ideally performed in the second trimester.
Thyroid ablation with radioactive iodine (I^131 ) is contraindicated because it
can cross the placentae, destroying the fetal thyroid.