Diagnostic Approach to Pulmonary Embolism

Initial Assessment and Imaging

• For pregnant women with suspected pulmonary embolism (PE) and a normal chest X-ray, lung scintigraphy (V/Q scan) is strongly recommended as the first-line imaging test rather than CT pulmonary angiography (CTPA) due to significantly lower maternal breast radiation exposure, as recommended by the American Thoracic Society and the American College of Chest Physicians 1, 2
• Begin with chest X-ray as the first radiation-associated procedure, followed by consideration of compression ultrasound of lower extremities if signs/symptoms of deep vein thrombosis (DVT) are present, according to the American College of Chest Physicians and the European Society of Cardiology 1, 2
• If the chest X-ray is abnormal, proceed with CTPA, while a normal chest X-ray should guide towards a V/Q scan, as suggested by the American College of Radiology 1

Diagnostic Accuracy and Mortality Prevention

• Pulmonary embolism is a leading cause of pregnancy-related mortality, accounting for 20% of maternal deaths in the US, highlighting the importance of accurate diagnosis, as reported by the American College of Radiology 3
• Both CTPA and V/Q scans have high negative predictive values for excluding PE, although the exact values are not provided, it is essential to consider the diagnostic accuracy in the context of pregnancy-related mortality 1

Radiation Exposure and Safety

• CTPA is associated with higher maternal breast radiation exposure, ranging from 10-60 mGy (older techniques) or 3-4 mGy (modern techniques), compared to V/Q scan, which exposes the breast to 0.28-1.07 mGy, as noted by the American College of Radiology and the European Heart Journal 1, 2
• The lifetime cancer risk increase from a single CTPA is minimal, with a factor of 1.0003-1.0007, according to the European Heart Journal 2
• Fetal radiation exposure from both CTPA and V/Q scan is well below the threshold for fetal harm (50-100 mGy), with CTPA exposing the fetus to 0.1-0.46 mGy and V/Q scan to 0.25-0.40 mGy, as reported by the European Heart Journal 2

Image Quality and Inconclusive Results

• V/Q scan techniques can be modified to reduce radiation, such as using half-dose protocols, which may help minimize exposure while maintaining diagnostic quality, as suggested by the American College of Radiology 1
• Technical modifications for CTPA, including iterative reconstruction, reduced kilovoltage, and shorter scan length, can help reduce radiation exposure while maintaining image quality, according to the European Heart Journal 2

Clinical Considerations and Pitfalls

• The American College of Chest Physicians recommends against overreliance on D-dimer testing due to its limited utility in pregnancy, as D-dimer levels physiologically increase throughout pregnancy 1
• Failure to start with chest X-ray and excessive concern about radiation are common pitfalls that can lead to delayed or inappropriate diagnosis, as noted by the American Thoracic Society and the European Society of Cardiology 1, 2
• Empiric anticoagulation should be considered while awaiting imaging if clinical suspicion is high and bleeding risk is low, according to the American College of Cardiology and the American College of Chest Physicians 1
• The decision to perform imaging should aim for diagnostic certainty rather than avoiding radiation at all costs, following the ALARA principle: "As Low As Reasonably Achievable" for radiation exposure, as recommended by the American College of Radiology and the European Society of Cardiology 4, 5
• It is recommended to document radiation dose to the mother in medical records, particularly if the fetus is in the field of view, and discuss risks and benefits with the patient, emphasizing that the risk of missing a potentially fatal diagnosis outweighs radiation concerns, as suggested by the American College of Radiology and the European Society of Cardiology 4, 5