How should a 34‑week pregnant woman with suspected pulmonary embolism be diagnosed and managed?

Management of Pulmonary Embolism at 34 Weeks Gestation

For a 34-week pregnant woman with suspected PE, initiate formal diagnostic workup immediately starting with bilateral lower extremity compression ultrasound if DVT symptoms are present, followed by chest X-ray to guide choice between V/Q scan (if CXR normal) versus CTPA (if CXR abnormal), and begin therapeutic anticoagulation with LMWH if clinical suspicion is high while awaiting test results. 1, 2

Immediate Diagnostic Approach

Initial Assessment and Risk Stratification

• Maintain a high index of suspicion as normal pregnancy symptoms (dyspnea, tachycardia, leg swelling) overlap with PE presentation 1, 2
• Do not use D-dimer testing to exclude PE in pregnancy due to poor specificity and inadequate sensitivity at 34 weeks gestation 2
• Do not use PESI or sPESI scoring systems as pregnancy-related physiologic changes (lower blood pressure, elevated heart rate, baseline dyspnea) make these scores invalid 1
• If high clinical suspicion exists with low bleeding risk, start therapeutic LMWH immediately while awaiting diagnostic results to prevent maternal and fetal death 1, 3

Diagnostic Algorithm

Step 1: Assess for DVT symptoms

• If leg pain, swelling, or other DVT symptoms present, perform bilateral compression ultrasound (CUS) of lower extremities first 1, 2
• If CUS positive: Begin treatment immediately—no further imaging needed 1, 2
• If CUS negative: Proceed to Step 2 1

Step 2: Obtain chest radiograph (CXR)

• CXR should be the first radiation-associated procedure performed 1, 2
• This helps triage between V/Q scan versus CTPA and may reveal alternative diagnoses 1, 2

Step 3: Choose imaging based on CXR result

If CXR is normal:

• Perform V/Q scan (lung scintigraphy) rather than CTPA 1, 2
• V/Q delivers significantly lower radiation to maternal breast tissue (lifetime breast cancer risk 1.011 for CTPA vs lower for V/Q) 2
• V/Q has similar diagnostic accuracy to CTPA in pregnancy (false-negative rate 0.5% vs 0.4%) 3
• Use reduced-dose protocol: half the usual Tc-99m macroaggregated albumin activity with increased scan time 1
• Prefer Xenon-133 ventilation scan over Tc-99m aerosol when possible for lower maternal dose 1

If CXR is abnormal:

• Perform CTPA rather than V/Q scan 1, 2
• CTPA provides better diagnostic yield when CXR abnormal and identifies alternative diagnoses 2, 3
• Use pregnancy-optimized protocol: automated bolus triggering, high iodine flux (4.5-6 ml/s flow rate), high iodine concentration (350-400 mg I/ml), and clear breathing instructions 1
• Be aware that 6-36% of CTPA studies in pregnancy are technically inadequate due to suboptimal vascular opacification 2

Step 4: If V/Q scan is nondiagnostic

• Proceed to CTPA rather than digital subtraction angiography 1
• Continue empiric anticoagulation during this workup if clinical suspicion remains high 1, 3

Acute Treatment Management

Anticoagulation for Confirmed or Highly Suspected PE

Standard therapeutic anticoagulation:

• Low-molecular-weight heparin (LMWH) is the preferred anticoagulant for treatment 1, 4
• Initiate therapeutic dosing immediately upon diagnosis or with high clinical suspicion 3
• Do not use DOACs (direct oral anticoagulants) as they cross the placenta and are contraindicated in pregnancy 1, 4
• Do not use warfarin during pregnancy 1
• LMWH is safe for breastfeeding postpartum 1

High-Risk PE Management

For hemodynamically unstable PE (hypotension, shock, cardiac arrest):

• Consider thrombolysis or surgical embolectomy for life-threatening PE 1
• Thrombolysis carries 18% major bleeding risk during pregnancy, 58% postpartum 1
• Fetal death occurs in 12% with thrombolysis, 20% with thrombectomy 1
• Avoid thrombolysis peri-partum except for life-threatening PE 1
• Unfractionated heparin (UFH) is typically used for acute high-risk PE management 1
• Maternal survival rates are 94% with thrombolysis, 86% with surgical thrombectomy 1

Delivery Planning and Peripartum Management

Timing Considerations at 34 Weeks

• At 34 weeks with recent PE diagnosis, coordinate with multidisciplinary team (obstetrics, anesthesia, hematology) for delivery planning 1
• Consider planned delivery to avoid spontaneous labor while fully anticoagulated 1

Anticoagulation Management Around Delivery

Timing of LMWH cessation:

• Wait ≥24 hours after last therapeutic LMWH dose before spinal/epidural needle insertion (assuming normal renal function) 1
• For high-risk situations (recent PE at 34 weeks), convert LMWH to UFH infusion ≥36 hours prior to planned delivery 1
• Stop UFH infusion 4-6 hours before anticipated delivery 1
• Verify activated partial thromboplastin time is normal before regional anesthesia 1

Postpartum anticoagulation:

• Do not give LMWH for ≥4 hours after epidural catheter removal 1
• Consider interim prophylactic LMWH dose post-cesarean section, then resume therapeutic dosing after ≥8-12 hour interval 1
• Continue anticoagulation for ≥6 weeks postpartum with minimum total treatment duration of 3 months 1, 4

Critical Pitfalls to Avoid

• Never rely on D-dimer alone to exclude PE in third trimester pregnancy 2
• Never delay anticoagulation if clinical suspicion is high while awaiting imaging 1, 3
• Never use standard risk scores (PESI/sPESI) designed for non-pregnant patients 1
• Never perform repeat CTPA without careful consideration if first study is nondiagnostic—consider V/Q scan instead 2
• Never insert spinal/epidural within 24 hours of therapeutic LMWH dose due to spinal hematoma risk 1
• Never use DOACs or warfarin during pregnancy 1

Multidisciplinary Coordination

• Involve obstetrics, maternal-fetal medicine, anesthesia, and hematology in care planning 1
• Document clear care pathways with written communication between teams 1
• Ensure all team members have expertise in PE management during pregnancy when possible 1