Pulmonary Embolism in Pregnancy: Recognizing the Signs That Cannot Be Ignored

Why Pregnancy Dramatically Increases Clot Risk

Pulmonary embolism (PE) — a blood clot in the lungs — is one of the most serious complications of pregnancy. According to the Centers for Disease Control and Prevention (CDC), venous thromboembolism (VTE), which includes both deep vein thrombosis (DVT) and pulmonary embolism, is a leading cause of maternal mortality in the United States and other developed countries.

Pregnancy increases the risk of VTE by approximately 4–5 times compared to non-pregnant women of the same age. This elevated risk persists throughout pregnancy and is highest in the 6 weeks following delivery (the postpartum period), when risk is approximately 20–80 times higher than baseline.

The reason for this dramatic increase lies in a phenomenon called Virchow's Triad — three factors that together promote clot formation:

1. Hypercoagulability (Increased Clotting Tendency)

Pregnancy causes significant changes in the coagulation system, increasing levels of clotting factors (particularly factors VII, VIII, X, and fibrinogen) while decreasing natural anticoagulants. This is an evolutionary adaptation to reduce hemorrhage during delivery — but it also increases clot risk throughout pregnancy.

2. Venous Stasis (Slowed Blood Flow)

The growing uterus compresses the inferior vena cava (the large vein returning blood from the legs to the heart), slowing venous return from the lower extremities. This pooling of blood in the leg veins creates conditions favorable for clot formation.

3. Endothelial Injury (Vessel Wall Damage)

Delivery — whether vaginal or cesarean — causes trauma to pelvic vessels. This vessel wall injury is a direct trigger for clot formation in the postpartum period.

Deep Vein Thrombosis: The Precursor to Pulmonary Embolism

Most pulmonary emboli originate as deep vein thromboses (DVTs) — clots that form in the deep veins of the legs or pelvis. A DVT becomes a PE when a portion of the clot breaks off and travels through the bloodstream to the pulmonary arteries, blocking blood flow to part of the lung.

Symptoms of DVT in Pregnancy

DVT symptoms can be subtle and are often dismissed as normal pregnancy discomfort:

• Leg swelling — particularly if asymmetric (one leg more swollen than the other)
• Calf or thigh pain — often described as aching, cramping, or tenderness
• Warmth and redness over the affected area
• Visible surface veins

The challenge is that leg swelling and discomfort are extremely common in normal pregnancy. The key distinguishing feature is asymmetry — normal pregnancy swelling tends to be bilateral, while DVT typically affects one leg more than the other.

Recognizing Pulmonary Embolism: Symptoms That Demand Immediate Attention

PE symptoms range from subtle to catastrophic. The classic presentation includes:

• Sudden shortness of breath — especially if it comes on rapidly and without exertion
• Chest pain — often sharp, worse with breathing (pleuritic chest pain)
• Rapid heart rate (tachycardia)
• Coughing up blood (hemoptysis) — less common but highly significant
• Lightheadedness or fainting
• Anxiety or sense of impending doom

In pregnancy, shortness of breath and rapid heart rate are common symptoms of normal physiological adaptation. This is precisely what makes PE so dangerous — the symptoms overlap with normal pregnancy changes, leading to delayed recognition.

Any sudden or unexplained worsening of shortness of breath, chest pain, or heart rate during pregnancy or the postpartum period should be evaluated immediately. Do not wait.

Risk Factors That Increase PE Risk During Pregnancy

While all pregnant women have elevated VTE risk, certain factors increase risk further:

• Personal or family history of DVT or PE
• Inherited thrombophilias (Factor V Leiden, Prothrombin gene mutation, Protein C or S deficiency, Antithrombin deficiency)
• Antiphospholipid syndrome
• Obesity (BMI > 30)
• Multiple pregnancy (twins or more)
• Immobility (bed rest, long-distance travel)
• Cesarean delivery (especially emergency cesarean)
• Preeclampsia
• Dehydration
• Age over 35
• Smoking

Women with multiple risk factors may be candidates for preventive anticoagulation therapy during pregnancy and the postpartum period.

Diagnosis: The Challenge of Imaging in Pregnancy

Diagnosing PE requires imaging, which presents challenges in pregnancy due to radiation exposure concerns.

D-Dimer Testing

D-dimer is a blood test that, when negative, effectively rules out VTE in non-pregnant patients. However, D-dimer levels rise naturally during normal pregnancy, making positive results difficult to interpret. A negative D-dimer in pregnancy is still useful for ruling out PE, but a positive result requires further imaging.

Compression Ultrasound

For suspected DVT, compression ultrasound of the leg veins is safe in pregnancy (no radiation) and is typically the first imaging step. If DVT is confirmed, treatment for PE is initiated without further lung imaging in some cases.

CT Pulmonary Angiography (CTPA)

CTPA is the gold standard for PE diagnosis. The radiation dose to the fetus is low (approximately 0.01–0.66 mGy, well below the threshold of concern at 50 mGy) and is generally considered acceptable when PE is clinically suspected. The risk of undiagnosed PE far outweighs the minimal radiation risk.

Ventilation-Perfusion (V/Q) Scan

An alternative to CTPA, V/Q scanning delivers lower radiation to the maternal breast tissue (relevant for breast cancer risk) but slightly higher fetal radiation. The choice between CTPA and V/Q scan depends on clinical circumstances and institutional protocols.

Treatment: Anticoagulation in Pregnancy

The primary treatment for DVT and PE in pregnancy is anticoagulation — blood-thinning medication that prevents clot growth and new clot formation.

Low Molecular Weight Heparin (LMWH)

LMWH (enoxaparin, dalteparin) is the preferred anticoagulant during pregnancy. It does not cross the placenta, has a predictable dose-response, and has an extensive safety record in pregnancy. It is administered by subcutaneous injection.

Unfractionated Heparin (UFH)

UFH may be used in specific circumstances, particularly near delivery when rapid reversal of anticoagulation may be needed.

Warfarin

Warfarin crosses the placenta and is associated with fetal abnormalities (warfarin embryopathy) in the first trimester. It is generally avoided during pregnancy but may be used postpartum.

Direct Oral Anticoagulants (DOACs)

DOACs (rivaroxaban, apixaban, dabigatran) are not recommended during pregnancy due to limited safety data and evidence of placental transfer in animal studies.

Prevention: What You Can Do

For most pregnant women, simple measures reduce VTE risk:

• Stay active — regular walking promotes venous return
• Stay hydrated — dehydration increases blood viscosity
• Wear compression stockings — particularly during long travel
• Avoid prolonged immobility — on long flights or car trips, move regularly
• Discuss risk factors with your provider — women at higher risk may benefit from prophylactic LMWH

*This content is for educational purposes only and does not constitute medical advice. Pulmonary embolism is a medical emergency. If you experience sudden shortness of breath, chest pain, or other symptoms described in this article, seek emergency medical care immediately.*