In a 25‑year‑old woman at 23 weeks gestation with two weeks of progressive dyspnea, inability to walk more than half a block, no peripheral edema or deep‑vein thrombosis signs, and an elevated D‑dimer of 728 ng/mL, how should pulmonary embolism be evaluated and managed?

Diagnostic Evaluation and Management of Suspected Pulmonary Embolism in Pregnancy

In this 25-year-old pregnant woman at 23 weeks gestation with progressive dyspnea limiting ambulation and an elevated D-dimer of 728 ng/mL, you should immediately proceed to bilateral compression ultrasonography of the lower extremities without relying on the D-dimer result to exclude PE, and if the ultrasound is negative, obtain a chest X-ray followed by imaging of the pulmonary vasculature. 1

Why the D-dimer Cannot Rule Out PE in This Case

• D-dimer rises physiologically by approximately 39% each trimester, with mean values of 0.58 mg/L in the first trimester, 0.83 mg/L in the second trimester (where this patient is), and 1.16 mg/L in the third trimester. 2, 3

• A D-dimer of 728 ng/mL (0.728 mg/L) is below the expected mean for the second trimester but cannot exclude PE because D-dimer testing in pregnancy has only 73% sensitivity and 15% specificity for PE, with a negative likelihood ratio of 1.8—inadequate to rule out disease. 2

• The American Thoracic Society/Society of Thoracic Radiology explicitly recommends against using D-dimer to exclude PE in pregnancy due to these severe limitations. 2, 3

Immediate Diagnostic Algorithm

Step 1: Bilateral Compression Ultrasonography First

• Perform bilateral compression ultrasonography of the lower extremities immediately, including Doppler assessment of the iliac veins, as this is the recommended first-line imaging test. 1, 3

• If DVT is detected, start therapeutic anticoagulation immediately without further imaging—finding a DVT warrants treatment regardless of whether PE is present. 1, 4

• If the ultrasound is negative but clinical suspicion remains high (as it should in this case given the severity of symptoms), proceed to pulmonary vascular imaging. 1

Step 2: Chest Imaging Strategy

• Obtain a chest X-ray as the first radiation-associated procedure to triage between subsequent imaging modalities. 1

• If the chest X-ray is normal, perform ventilation-perfusion (V/Q) lung scintigraphy rather than CTPA, as this delivers significantly lower maternal radiation exposure (0.98-1.07 mGy vs. 10-60 mGy with CTPA). 1

• If the chest X-ray is abnormal, proceed directly to CTPA to maximize diagnostic yield and identify alternative diagnoses. 1

• If V/Q scan results are nondiagnostic, perform CTPA to achieve diagnostic certainty given the potentially fatal consequences of missing PE. 1

Step 3: Consider Iliac Vein Thrombosis

• If the patient has whole-leg swelling or pain in the buttock, groin, flank, or abdomen (not mentioned in this case but important to assess), and standard compression ultrasound is negative, obtain Doppler ultrasound of the iliac veins or MRI venography to evaluate for iliac vein thrombosis, which is more common on the left side in pregnancy due to compression by the enlarged uterus. 1, 3

Anticoagulation Management if PE or DVT is Confirmed

Immediate Treatment

• Start therapeutic low-molecular-weight heparin (LMWH) immediately if imaging confirms PE or DVT. 4, 3

• Dosing regimens:

  • Enoxaparin 1 mg/kg subcutaneously twice daily, OR 4
  • Dalteparin 100 IU/kg subcutaneously twice daily 4, 3

• Target peak anti-Xa levels of 0.6-1.2 IU/mL measured 4-6 hours after injection. 4, 3

Duration of Treatment

• Continue therapeutic anticoagulation throughout pregnancy and for at least 6 weeks postpartum, with a minimum total duration of 3 months. 4, 3

Critical Pitfalls to Avoid

• Do not delay imaging while awaiting or interpreting D-dimer results when clinical suspicion is moderate to high, as in this case with severe functional limitation. 3

• Do not dismiss severe dyspnea as "normal pregnancy breathlessness"—while mild dyspnea is common in pregnancy, the inability to walk more than half a block represents severe functional impairment requiring urgent evaluation. 1

• Do not use direct oral anticoagulants (DOACs) or warfarin in pregnancy, as these cross the placenta and can cause fetal harm; LMWH is the only safe anticoagulant option. 1, 4, 3

• Do not use unfractionated heparin preparations containing benzyl alcohol, as this poses a risk of fetal toxicity. 4

• Do not rely on clinical prediction scores like PESI or sPESI in pregnancy, as physiologic changes (lower blood pressure, higher heart rate, baseline dyspnea) render these scores invalid. 1

Multidisciplinary Coordination

• Ensure consultation with obstetrics before discharge and establish clear follow-up plans with documented responsibility for ongoing care. 1

• All pregnant women with suspected or confirmed PE should be reviewed by a consultant prior to any discharge decision. 1