Carbimazole dosage and sequential measurements of fT4 , TSH, and TRAb in a 25-year-old woman discovered to have hyperthyroidism due to Graves’ disease while attending an infertility clinic. Within weeks of control of the hyperthyroidism she became pregnant. Note (1) the trimester-adjustedreference range for fT4; (2) the fall in TRAb concentration during treatment with carbimazole, and the further fall during pregnancy; (3) the low dose of carbimazole required to maintain euthyroidism during pregnancy and the withdrawal of the antithyroid drug 4 weeks before the expected date of delivery; (4) the development of post-partum thyroiditis, characterized by transient hyperthyroidism followed by an equally short-lived episode of hypothyroidism in the absence of TRAb. Normal ranges are indicated by the shaded areas. CBZ: carbimazole.