A 28-year-old lady presents with a 3-day history of a painful swollen right calf. Past medical history is relevant for 2 abortions at 11th week of gestations. CBC showed: WBC = 8.5/ mm3 (4000-11000) HGB= 9.8 g/dl (13.6- 17.7) platelets= 120.000 (130-400,000/mm3) coagulation screen shows: PT= 13s (control= 13), APTT= 78s (control 36) What is the most likely cause of her illness?