This patient, who is pregnant and has a clinical suspicion for pulmonary embolism (PE), should undergo lower extremity venous duplex ultrasonography. Because anticoagulant therapy for PE and deep venous thrombosis (DVT) is similar, diagnosing a DVT noninvasively through ultrasonography would allow immediate initiation of therapy and avoid fetal exposure to radiation and contrast, which are involved in other studies for diagnosing PE. However, a normal lower extremity study for DVT does not exclude the presence of a PE in a patient with a reasonable pretest probability based on clinical features, such as this woman. If her ultrasound is normal, a ventilation-perfusion (V/Q) lung scan is the next preferred modality. If a V/Q scan is unavailable, CT pulmonary angiography is the next diagnostic choice.

Unfortunately, no validated clinical prediction rules exist for assessing pretest probability of PE in pregnant women. Additionally, D-dimer levels are normally elevated during pregnancy. Therefore, D-dimer testing has minimal clinical utility in evaluating for the presence of PE or DVT.