What is the test of choice for diagnosing pulmonary embolism (PE) in pregnancy?

Diagnostic Approach for Pulmonary Embolism in Pregnancy

For pregnant women with suspected pulmonary embolism (PE), a chest radiograph (CXR) should be performed as the first radiation-associated procedure, followed by lung scintigraphy (V/Q scan) if the CXR is normal or CT pulmonary angiography (CTPA) if the CXR is abnormal. 1

Initial Assessment

• Maintain a high index of suspicion for PE in pregnant women, as normal pregnancy can mimic some PE symptoms such as mild shortness of breath, tachycardia, and leg edema 1
• Common clinical presentations of PE in pregnancy include dyspnea (62%), pleuritic chest pain (55%), cough (24%), and sweating (18%) 1
• There are no validated clinical prediction rules specifically for determining pre-test probability of PE in pregnant patients, making clinical judgment crucial 1, 2
• D-dimer testing should not be used to exclude PE in pregnancy due to its poor specificity, as levels naturally increase during pregnancy 1, 2

Diagnostic Algorithm

Step 1: Assess for DVT symptoms

• In pregnant women with suspected PE and signs/symptoms of deep venous thrombosis (DVT), perform bilateral venous compression ultrasound (CUS) of lower extremities 1
• If CUS is positive, initiate anticoagulation treatment 1
• If CUS is negative, proceed with imaging studies of the pulmonary vasculature 1

Step 2: Chest Radiography

• For all pregnant women with suspected PE, perform a chest radiograph (CXR) as the first radiation-associated procedure 1
• CXR helps triage between lung scintigraphy and CTPA 1

Step 3: Choose appropriate imaging based on CXR results

• If CXR is normal: Perform lung scintigraphy (V/Q scan) rather than CTPA 1
• If CXR is abnormal: Perform CTPA rather than lung scintigraphy 1, 3

Rationale for Imaging Selection

• V/Q scanning delivers lower radiation dose to maternal breast tissue compared to CTPA (0.98-13.5 mGy vs. 10-60 mGy) 1
• CTPA has been associated with a higher lifetime relative risk of radiation-induced breast cancer (estimated at 1.011 for a 25-year-old woman) 1, 2
• Both V/Q scan and CTPA have high negative predictive values (100% and 97.5% respectively) for excluding PE in pregnancy 4
• V/Q scan is more likely to yield diagnostic results when CXR is normal 2, 4
• CTPA provides better diagnostic yield and can identify alternative diagnoses when CXR is abnormal 1, 3

Management of Non-Diagnostic Results

• If V/Q scan is non-diagnostic, further diagnostic testing is recommended rather than clinical management alone 1
• In patients with a non-diagnostic V/Q scan who require further investigation, CTPA is recommended rather than digital subtraction angiography 1
• Technically inadequate CTPA studies occur in 6-36% of pregnant women, primarily due to suboptimal vascular opacification and respiratory motion artifacts 2

Radiation Considerations

• Both imaging modalities expose the fetus to radiation, but at doses well below the threshold associated with fetal complications (50-100 mSv) 1
• Estimated fetal radiation exposure: V/Q scan (0.1-0.6 mGy) vs. CTPA (0.05-0.5 mGy) 1
• Maternal breast radiation exposure: V/Q scan (0.16-1.2 mGy) vs. CTPA (3-10 mGy) 1
• V/Q SPECT is associated with low fetal and maternal radiation exposure and shows promise in PE diagnosis in pregnancy 1

Special Considerations

• The choice between V/Q scan and CTPA may be influenced by local expertise and resources 1
• For unstable patients or when studies are not available promptly, consider empiric anticoagulation while awaiting diagnostic results 2
• Low molecular weight heparin (LMWH) is the treatment of choice for PE during pregnancy 1
• Overdiagnosis of PE can have significant lifelong implications including bleeding risk at delivery, contraception limitations, and thromboprophylaxis requirements in future pregnancies 1, 5