What is the next step in managing a 24-week pregnant woman with symptoms concerning for pulmonary embolism (PE), such as intermittent dyspnea, tachycardia, and chest heaviness, and an elevated D-dimer level?

Management of Suspected PE in 24-Week Pregnant Woman with D-Dimer 360

An elevated D-dimer of 360 ng/mL in a 24-week pregnant woman with symptoms concerning for PE should NOT be used to exclude PE—proceed directly to bilateral lower extremity compression ultrasound if DVT signs are present, or to chest imaging if no DVT signs exist. 1, 2

Why D-Dimer Cannot Exclude PE in Pregnancy

The American Thoracic Society explicitly recommends against using D-dimer to exclude PE in pregnant women, even when the value appears "normal" by non-pregnancy standards 1. This recommendation is based on critical evidence:

• D-dimer has only 73% sensitivity for PE in pregnancy, meaning 27% of actual PEs would be missed if you relied on this test 2, 3
• The specificity is only 15%, making it essentially useless for ruling in disease 3
• The negative likelihood ratio is 1.8, which provides virtually no diagnostic value 4
• D-dimer levels physiologically increase throughout pregnancy—by the second trimester (where this patient is), mean levels reach approximately 0.58-0.70 mg/L (580-700 ng/mL), making a value of 360 ng/mL actually relatively low for gestational age but still unreliable 3

Algorithmic Approach to This Patient

Step 1: Assess for DVT Signs and Symptoms

If leg swelling, pain, or asymmetric calf circumference ≥2 cm is present:

• Perform bilateral compression ultrasound (CUS) of lower extremities immediately 1, 3
• If positive: Start anticoagulation without further testing 1, 3
• If negative: Proceed to Step 2 1

If NO signs or symptoms of DVT (which appears to be this case):

• Skip lower extremity ultrasound and proceed directly to pulmonary vascular imaging 1

Step 2: Obtain Chest X-Ray First

The American Thoracic Society strongly recommends chest X-ray as the first radiation-associated procedure 1, 5:

• Fetal radiation exposure is <0.01 mGy—approximately 1/5,000,000th of the safety threshold 5
• The risk of missing PE far outweighs negligible radiation risk 5
• CXR results will guide whether to proceed with V/Q scan versus CTPA 1

Step 3: Choose Definitive Imaging Based on CXR Results

If CXR is normal:

• Proceed with ventilation-perfusion (V/Q) lung scan as the next test 1
• V/Q scanning minimizes maternal breast radiation exposure compared to CTPA 1
• 75-94% of V/Q scans in pregnancy yield diagnostic results (high probability, very low probability, or normal) 1

If CXR is abnormal:

• Proceed with CT pulmonary angiography (CTPA) instead 1
• CTPA provides faster diagnosis and can identify alternative diagnoses when CXR is abnormal 1

If V/Q scan is nondiagnostic (intermediate probability):

• Proceed to CTPA for definitive diagnosis rather than managing clinically 1

Critical Pitfalls to Avoid

Do not dismiss symptoms as "normal pregnancy" 2:

• While dyspnea and tachycardia occur in normal pregnancy, this patient has the triad of intermittent dyspnea, tachycardia, AND chest heaviness—warranting full investigation 2
• PE accounts for 20% of maternal deaths in developed countries 5
• Only 2-7% of investigated pregnant women actually have PE, but the consequences of missing it are catastrophic 2

Do not delay imaging due to radiation concerns 5:

• All recommended imaging modalities deliver radiation doses thousands of times below the 50-100 mGy threshold for fetal harm 5
• Missing maternal PE poses far greater risk to both mother and fetus than diagnostic radiation 5

Do not use clinical prediction rules like Wells score alone 2:

• These have not been validated in pregnancy and cannot reliably predict PE in this population 2, 6

Documentation and Patient Counseling

Document clearly that:

• D-dimer cannot exclude PE in pregnancy due to 73% sensitivity 2, 3
• Radiation exposure from diagnostic imaging is negligible compared to safety thresholds 5
• The clinical suspicion warrants proceeding with the diagnostic algorithm regardless of D-dimer value 1, 2