Diagnosis of Pulmonary Embolism in Pregnancy.

Pulmonary embolism (PE) is a significant cause of obstetric morbidity and mortality. However, over diagnosis related to excessive use of diagnostic testing is also associated with long term major health issues, including impact on future pregnancies and subsequent health care. Accurate diagnosis of PE depends on knowledge of the prevalence of PE in the pregnant population, the a priori probability of a PE based on specific findings in a given patient and understanding of the accuracy of computed tomographic pulmonary arteriography (CTPA), the dominant diagnostic modality employed for this diagnosis. Venous thromboembolism (VTE) is widely considered to be more common in pregnancy. However, this term includes both deep venous thrombosis (DVT) as well as PE. While the former appears to be more common, published data on the prevalence of PE in pregnancy show little or no increase relative to the general population. Given the published data on the sensitivity and specificity of CTPA, a positive reading is more likely to be a false positive unless the probability of a PE in a given patient is at least 5% (a two-hundred-fold increase from baseline). Doubling the probability to 10% (a four-hundred-fold increase) only improves the positive predictive value to about 67%. Strategies to refine the a priori probability of a PE in a given patient are detailed, including scoring systems and D-dimer measurements. A careful history and physical examination and thoughtful development of a differential diagnosis are key elements of clinical practice and should include both the likelihood of each possible diagnosis and the accuracy of diagnostic modalities. This approach should precede the application of a given algorithm. Such a structured approach can decrease utilization and limit false positive diagnoses without increasing morbidity or mortality.