Which of the following is not a risk factor of venous thromboembolism?

Ambulating, or being active and moving around, is generally considered to be protective against venous thromboembolism (VTE) rather than a risk factor. Regular movement helps improve venous return and circulation, reducing the likelihood of blood pooling in the veins, which is a significant contributor to the formation of clots.

In contrast, increased age, pelvic trauma, and obesity are well-established risk factors associated with VTE. Aging often comes with physiological changes and comorbidities that can increase clotting risk. Pelvic trauma can result in immobility, damage to veins, or increased vascular stress, which heightens the chance of thrombosis. Obesity affects venous hemodynamics and can lead to a state of hypercoagulability, making individuals more susceptible to thromboembolic events.

Thus, while age, trauma, and obesity can contribute to the risk of developing VTE, ambulating helps mitigate that risk, distinguishing it as the option that is not a risk factor.