Pregnancy and the Increased Risk of Developing Blood Clots

Topic Overview

Pregnant women have a higher risk of deep vein thrombosis and pulmonary embolism.^{footnote 1}

What raises the risk of blood clots during pregnancy?

The three main risk factors (things that increase risk) for developing deep vein thrombosis and pulmonary embolism are abnormal clotting, reduced blood flow, and damage to the veins. These risks are all higher during pregnancy, most likely because of:

• Changes in hormone levels and blood composition that influence clotting.
• Reduced blood flow in the legs due to the weight of the fetus pressing upon veins.
• Injury to veins during delivery or surgery.
• Inactivity after cesarean section surgery or delivery.

Women who are obese, are older than 35, or have a family or personal history of blood clots have a higher risk of developing a clot that can lead to pulmonary embolism.

After delivery, the risk for blood clots is higher than during pregnancy. This risk usually returns to normal after a few weeks after delivery.^{footnote 2}

If a woman has a cesarean section, she is even more likely to develop one or more of these clots.

Who is screened for risk of blood clots?

Women with the following history may be screened for genetic factors that can increase the risk of forming blood clots:

• A personal or family history of deep vein thrombosis or pulmonary embolism
• Repeated miscarriages, especially during the second trimester
• Stillbirth
• Severe or recurrent low birth weight (intrauterine growth restriction)
• Preeclampsia

How are blood clots prevented?

For pregnant women who are more likely to develop blood clots, several methods may be used to prevent deep vein thrombosis and pulmonary embolism. These include:

• Wearing compression stockings.
• Taking heparin, an anticoagulant medicine.

How are blood clots treated?

A pregnant woman who is diagnosed with deep vein thrombosis or pulmonary embolism will work with her doctor to decide which anticoagulant medicine to take during pregnancy. She may take heparin, because it has not been shown to affect the fetus.

After delivery, the woman might take another anticoagulant for a few weeks or a few months.