A 28-year-old woman presented to emergena denartment with sudden onse dyspnea and pleuritic chest pain. She has been taking combined oral contraception for 3 years. Vital signs showed blood pressure 110/70 mmHg, heart rate 110 bpm, and SPO2 92% on room air. D-dimer is elevated. Which of the following is the most important risk factor for pulmonary embolism?