One of your obstetric patients presents to the office at 25 weeks complaining of severe left calf pain and swelling. The area of concern is slightly edematous, but no erythema is apparent. The patient demonstrates a positive Homan sign, and you are concerned that she may have a deep vein thrombosis. Which of the following diagnostic modalities do you order?

Noninvasive modalities are currently the preferred tests for diagnosing venous thromboembolism. Venography is still the gold standard, but it is not commonly used because it is cumbersome to perform and expensive and has serious complications. Real-time ultrasonography or color Doppler ultrasound is the procedure of choice to detect proximal deep vein thrombosis. MRI and CT scanning are used in specific cases when ultrasound findings are equivocal.