Graves' disease and human chorionic gonadotropin (hCG)-mediated hyperthyroidism are the most common causes of hyperthyroidism during pregnancy; toxic adenomas and toxic multinodular goiter are seen less commonly. Graves’ hyperthyroidism (defined as hyperthyroidism that is the result of stimulation of the thyroid by thyrotrophin receptor stimulating antibodies (TRAb)) is the commonest cause of hyperthyroidism in young women (about 85% of cases). During pregnancy, the hormone HCG (human chorionic gonadotropin) is produced. HCG is the hormone that "pregnancy tests" detect.
HCG increases to a peak at around 12 weeks. It has mild thyroid stimulating effects and, as a result, can cause some symptoms of hyperthyroidism. HCG is in part responsible for the nausea during the first trimester. In situations of multiple pregnancies (e.g, twins) HCG levels are even higher, and symptoms more…
