Upshaw–Schulman syndrome (USS) involves a congenital deficiency of von Willebrand factor-cleaving metalloprotease (ADAMTS13) activity due to gene mutations. Female patients develop overt thrombotic thrombocytopenic purpura (TTP) caused by a decline of ADAMTS13 activity in pregnancy. A 23-year-old nulliparous Japanese woman died due to severe, rapid progression of TTP with intrauterine fetal death at 20 weeks of gestation after its onset, even though she underwent intensive treatment which included plasma exchange. She had a history of idiopathic thrombocytopenic purpura at the age of 3 years. The patient's ADAMTS13 activity was of very low level. It should be borne in mind that there is the possibility of rapidly progressive fulminant USS during pregnancy.