Did you know that pulmonary embolism causes up to 20% of maternal deaths during pregnancy? The diagnosis is challenging, because pregnant women are often dyspneic, tachycardic, and have leg swelling at baseline. The best test, CT-angiography uses radiation that is, obviously, to be avoided at all costs for its teratogenic effects on the fetus.
Ann Leung et al have produced a Clinical Practice Guideline for the American Thoracic Society and Society of Thoracic Radiology, who share it with us in the Blue Journal. Authors lament that the quality of the evidence base guiding decisions here is “very low or low.” Nevertheless, they created a diagnostic algorithm whose logic distills down to this:
- If there are leg symptoms (edema), get compression ultrasound of both legs. Treat for DVT* if positive.
- If there are no leg symptoms or ultrasound is negative, get a chest X-ray.
- If the chest X-ray is normal, get a V/Q scan.
- If the chest X-ray is abnormal, or if V/Q scan is nondiagnostic, get a CT-angiogram.
- Don’t check a D-dimer, ever.
The teratogenic risk to a fetus from a CT’s radiation is unknown, but can theoretically occur at any dose. Iodinated and gadolinium contrast cross the placenta and enter the fetus’s bloodstream; there have been no demonstrated adverse effects (e.g., neonatal hypothyroidism from free iodine). Gadolinium has been shown to be carcinogenic only at very high exposures.
Leung AN et al. An Official American Thoracic Society/Society of Thoracic Radiology Clinical Practice Guideline: Evaluation of Suspected Pulmonary Embolism In Pregnancy. Am J Respir Crit Care Med 2011;184:1200-1208.