Considerations before conception

If a woman with hyperthyroidism is planning to become pregnant, ensure a stable euthyroid state is achieved before conception.

Antithyroid drugs increase the risk of congenital abnormalities. Many patients with Graves disease, particularly young patients with a first episode of mild hyperthyroidism, can achieve remission after a period of treatment with an antithyroid drug. Although remission is often temporary, relapse within the first few months of stopping antithyroid drug therapy is uncommon in patients whose TSH-receptor antibody normalised during treatment. Well-timed remission could avoid the need for an antithyroid drug in the first trimester of pregnancy.

Propylthiouracil and carbimazole are classified as category D by the Therapeutic Goods Administration (TGA)¹ in relation to use in pregnancy because of the risk of congenital abnormalities. If treatment is required during pregnancy, propylthiouracil is favoured over carbimazole during the first trimester, as it is associated with less severe congenital abnormalities. Switch existing carbimazole therapy to propylthiouracil before conception. To prevent overtreatment and possible neonatal hypothyroidism or goitre, and to minimise the risk of fetal congenital abnormalities, use the lowest effective dose of antithyroid drug therapy.

A patient with recurrent, severe or refractory hyperthyroidism who is planning to become pregnant should be referred to a specialist for advice before conception.