[The use of antithyroid drugs should be reduced as much as possible in the first trimester]

The treatment of choice for hyperthyroidism in pregnancy is antithyroid drugs, but the potential risk of birth defects is of major concern. For the use of thiamazole and carbimazole, there is consistent evidence of an increased risk of birth defects, which are often severe. For the use of propylthiouracil, the evidence is less clear. These birth defects may be less severe, and a Danish study which included all birth defects diagnosed before the age of two years showed an increased risk of birth defects in the face and neck region and in the urinary system after the use of propylthouracil.