What is the role of chest X-ray in diagnosing pulmonary embolism (PE) in a pregnant patient with a history of PE and potential miscarriage risk, currently on Lovenox (enoxaparin) therapy?

Role of Chest X-Ray in Diagnosing PE in Pregnant Patients

Chest X-ray should be performed as the first radiation-based imaging study in all pregnant patients with suspected pulmonary embolism, regardless of anticoagulation status or pregnancy complications. 1, 2, 3

Why Chest X-Ray Comes First

The American Thoracic Society explicitly recommends chest X-ray as the initial radiation-associated procedure in the diagnostic algorithm for suspected PE in pregnancy. 1, 3 This recommendation serves a critical strategic purpose: the chest X-ray result determines which subsequent imaging modality is most appropriate.

The Diagnostic Algorithm

If chest X-ray is normal:

• Proceed directly to V/Q (ventilation-perfusion) lung scintigraphy as the next imaging test rather than CT pulmonary angiography (CTPA). 1, 3
• This strong recommendation is based on optimizing diagnostic yield while minimizing radiation exposure. 1

If chest X-ray is abnormal:

• Proceed to CTPA as the next imaging test rather than V/Q scanning. 3
• Abnormal chest X-rays reduce the diagnostic accuracy of V/Q scans, making CTPA the preferred choice. 3

Radiation Safety Context

The radiation exposure from chest X-ray is extraordinarily minimal and poses no meaningful risk to the fetus:

• Fetal radiation dose from chest X-ray is less than 0.01 mGy. 4
• This represents approximately 1/5,000,000th of the established safety threshold for fetal harm (50-100 mGy). 4
• The American Thoracic Society and European Society of Cardiology both emphasize that this dose is well below any level associated with fetal complications. 4

The risk of missing PE far outweighs the negligible radiation risk from chest X-ray. 2, 4 PE remains the leading cause of pregnancy-related maternal death in developed countries, accounting for 20% of maternal deaths in the United States. 4

Critical Pitfalls to Avoid

Do not skip chest X-ray and proceed directly to CTPA or V/Q scan. The chest X-ray result is essential for determining the optimal subsequent imaging pathway. 1, 3

Do not delay imaging due to radiation concerns. Delaying or avoiding necessary imaging poses greater risk to both mother and fetus than the radiation exposure itself. 4 The consequences of missing PE are catastrophic, while chest X-ray radiation is equivalent to a few days of natural background exposure. 4

Do not rely on clinical features alone to exclude PE. No individual clinical feature or combination of features reliably predicts PE in pregnancy. 2 Dyspnea (62% of cases), pleuritic chest pain (55%), and tachycardia are common but non-specific. 1, 2

Do not use D-dimer to exclude PE in pregnant patients. The American Thoracic Society explicitly recommends against using D-dimer to exclude PE in pregnancy, as it has only 73% sensitivity and false negatives are documented in confirmed PE cases. 1, 2, 3

Special Considerations for Your Patient

Your patient has multiple high-risk features that mandate thorough diagnostic evaluation:

• Prior PE history: This is the strongest risk factor for recurrent PE in pregnancy. 2
• Already on Lovenox: Anticoagulation does not eliminate PE risk, and breakthrough events can occur.
• Potential miscarriage risk: This does not change the diagnostic approach. The chest X-ray radiation dose poses no risk to early pregnancy or fetal development. 4

If clinical suspicion is high and bleeding risk is low, initiate or continue therapeutic anticoagulation while awaiting diagnostic test results. 1, 3 Two studies in non-pregnant patients demonstrated that early anticoagulation in the emergency department reduced adverse outcomes including mortality. 1

Additional Diagnostic Steps

If DVT symptoms are present (leg swelling, pain, erythema): Perform bilateral compression ultrasound of lower extremities before pulmonary imaging. 1, 3 If positive for proximal DVT, continue therapeutic anticoagulation without further imaging. 3

If no DVT symptoms: Proceed directly to pulmonary vascular imaging (chest X-ray first) rather than lower extremity ultrasound, as this is more cost-effective. 1, 3

If V/Q scan is non-diagnostic: Proceed to CTPA rather than clinical management alone. 1, 3 Do not use digital subtraction angiography. 1

If CTPA is indeterminate and clinical suspicion remains high: Continue therapeutic anticoagulation while pursuing additional diagnostic testing. 3