Transient hyperthyroidism of hyperemesis gravidarum: a sheep in wolf's clothing

BACKGROUND: Transient hyperthyroidism of hyperemesis gravidarum (THHG) is a self-limiting hyperthyroidism occurring in the context of hyperemesis gravidarum. METHODS: A literature search of MEDLINE was undertaken, and a case report of a woman with THHG in pregnancy is described. RESULTS AND CONCLUSIONS: Because thyroid function tests cannot distinguish Graves disease from THHG, the diagnosis of THHG rests largely on the concurrent development of hyperemesis and hyperthyroidism and the absence of signs and symptoms of hyperthyroidism before and during pregnancy. THHG might be responsible for 40% to 70% of thyroid function abnormalities in pregnancy. Both the thyroid function abnormalities and hyperemesis are related to elevated levels of human chorionic gonadotropin. THHG resolves by 18 weeks of pregnancy without sequelae. No treatment is required. Diagnosis of THHG by the primary care provider can prevent unnecessary treatment or referral for specialty care.