A 28-year-old woman presents to the emergency department 10 days after an uncomplicated vaginal delivery with acute left calf swelling, erythema, and tenderness. She reports the symptoms began this morning. Vital signs are stable (BP 120/78 mmHg, HR 88/min, RR 14/min, Temp 36.9°C, SpO2 99%). Physical examination reveals left calf edema and palpable cord-like structure along the distribution of the popliteal vein. Compression ultrasound confirms acute left popliteal vein thrombosis. D-dimer is elevated at 2.8 mcg/mL (normal <0.5). She denies dyspnea, chest pain, hemoptysis, or leg pain prior to delivery. Past medical history is significant only for the current pregnancy. She is not on oral contraceptives and has no family history of thrombosis. Which of the following is the most likely predisposing factor for this patient's presentation?

1. A)Factor V Leiden heterozygosity
2. B)Antithrombin III deficiency
3. C)Protein C deficiency
4. D)Lipoprotein(a) elevation
5. E)Pregnancy and the immediate postpartum periodGABARITO