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
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:

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.



  1. American College of Obstetricians and Gynecologists (2011). Thromboembolism in pregnancy. ACOG Practice Bulletin No. 123. Obstetrics and Gynecology, 118(3): 718-729.
  2. Tapson VF, Becker RC (2007). Venous thromboembolism. In EJ Topol, ed., Textbook of Cardiovascular Medicine, 3rd ed., pp. 1569-1584. Philadelphia: Lippincott Williams and Wilkins.


ByHealthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD – Internal Medicine
Adam Husney, MD – Family Medicine
Specialist Medical Reviewer Jeffrey S. Ginsberg, MD – Hematology

Current as ofMarch 20, 2017