This patient's secondary amenorrhea, markedly enlarged uterus (infraumbilical mass), and hyperthyroidism are consistent with a hydatidiform mole, an abnormal gestation that results from the fertilization of an empty ovum. Additional clinical features can include hyperemesis gravidarum, abnormal vaginal bleeding, and bilateral enlarged ovaries (eg, theca lutein cysts). Risk factors for hydatidiform mole include extr