Introduction

Pulmonary embolism PE is a clot of blood in the lung blood vessels that decreases or restricts the blood flow to the lung causing low oxygen levels. This can damage the lungs and heart and could lead to death if not diagnosed and treated promptly however, if treated quickly it’s rarely fatal.

The clot usually forms in the veins of the legs or arms and then moves to the lungs.

PE is one of the most common blood vessel diseases, it ranks third after heart attack and stroke.¹

Signs and symptoms of pulmonary embolism

The signs and symptoms of PE differ from one person to another depending on the size of the clot, the extent of the damage to the lung and the concomitant presence of heart or lung disease.²

These symptoms include:

• Shortness of breath
• Chest pain
• Syncope
• Cough
• Irregular heartbeat
• Dizziness
• Cyanosis
• Leg pain

You might experience some or all of these symptoms.

The risk of having PE increases by 5-fold during pregnancy and immediately after delivery making it one of the most common causes of maternal mortality.³

The reasons for this might be due to hypercoagulable state during pregnancy.⁴ Hypercoagulability might be due to:

• Increased level of coagulation factors in preparation for delivery.
• Increased venous stasis in lower limbs caused by pregnancy hormones.

Some women are more at risk of having PE during pregnancy.⁵ These risk factors are:

• Previous venous thromboembolism during pregnancy.
• Increased BMI
• Multiple pregnancies
• Hyperemesis
• Increased maternal age
• Thrombophilia
• Family history of blood clots
• Delivery by cesarean section
• Smoking
• Decreased mobility

Diagnosis of pulmonary embolism in pregnancy

The most accurate way to diagnose PE in pregnancy is laboratory imaging. However, this might hold a risk of radiation to both the fetus and the mother. For this reason, ultrasonography should be considered first, if it gives positive results the treatment should be started.⁵

Negative ultrasonography does not exclude PE, therefore further testing using imaging should be done.

Because the symptoms of PE in pregnancy can also be due to other factors like pneumonia or the pregnancy itself, a chest radiograph should be done prior to imaging to exclude or define these factors.

Imaging for PE diagnosis includes:

1. Spiral CT pulmonary angiography: It uses IV contrast followed by a CT scan. and might not detect small or peripheral emboli.
2. Ventilation-perfusion scan: is a two-phase test:
   • Ventilation phase: inhalation of radionuclide gas by the patient to test the flow of air to the lung
   • Perfusion phase: IV administration of radioactive contrast to test blood flow to the lung

Then comparing the two imaging, areas where there is airflow but not blood indicate the presence of a clot.

Treatment of pulmonary embolism in pregnancy

Therapeutic treatment of pulmonary embolism in pregnancy includes the use of heparins whether low molecular weight heparin(LMWH) or unfractionated heparin because they are both safe for both mother and baby, as they can’t cross the placenta and they are both non-teratogenic. 

LMWH is preferred over heparin because it does not need close monitoring of prothrombin time and is less likely to cause thrombocytopenia.

LMWH can induce side effects such as skin reactions and increased risk of bleeding. If skin lesions occur, switching to another type of LMWH is an option.

If LMWHs do not give the therapeutic effect needed or heparin-induced thrombocytopenia occurs, your doctor will switch your medicine to a non-heparin anticoagulant such as fondaparinux or danaparoid sodium.

Danaparoid is safe and can not cross the placenta however fondaparinux can cross the placenta in small amounts so it should never be the first choice.

Another anticoagulant, i.e vitamin K antagonists such as warfarin are contraindicated during pregnancy because:

• Can cross placenta 
• Teratogenic: inhibits vitamin K-dependent proteins which are needed to form cartilages and bones and can lead to warfarin-associated embryopathy
• Increase the risk of fetal loss in the first trimester
• Increase the risk of  fetal cerebral haemorrhage during delivery

If PE leads to life-threatening hemodynamic instability, systemic thrombolytic agents should be considered.⁶

Summary

Pulmonary embolism is a serious condition of a blood clot in the lung that if not treated timely and appropriately can lead to death.

There is an increased risk of having PE during pregnancy due to the change in coagulation status of a pregnant woman caused by pregnancy hormones.

Pregnancy can complicate the choices of diagnosing and treating PE because both the mother and the child should be considered carefully during the selection of the diagnosis and treatment approach.

Heparins are the first choice of treatment as they are relatively safe for they are not capable of crossing the placenta, and they are not teratogenic.