Pregnancy and the increased risk of developing blood clots

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Pregnancy and the increased risk of developing blood clots

The three main risk factors that increase the risk of developing deep vein thrombosis and/or 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 C-section surgery or delivery.

Women who are overweight, 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.¹

The risk of developing deep vein thrombosis or pulmonary embolism quadruples soon after giving birth.² If a woman has a cesarean section, she is even more likely to develop one or more of these clots.³ This risk usually returns to normal around 2 weeks after delivery.¹

Early research has led some health professionals to recommend that women with the following history be screened for genetic factors that can increase the risk of forming blood clots:¹

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

Methods that may be used to prevent deep vein thrombosis and pulmonary embolism in pregnant women who have an increased risk of developing blood clots include:

• Wearing compression stockings.
• Taking unfractionated heparin (UH) or low-molecular-weight heparin (LMWH).

Treatments that can be used for pregnant women who are diagnosed with deep vein thrombosis or pulmonary embolism include:

• Heparin (an anticoagulant medication). Unfractionated heparin or low-molecular-weight heparin is used because they are not shown to affect the fetus.
• Warfarin (another type of anticoagulant). This medication can be used after delivery.² Warfarin may cause miscarriage or birth defects if used during pregnancy, especially in the first 6 to 9 weeks.¹ There is also an increased risk of bleeding in the fetus and the mother, particularly during the third trimester.

If a woman has deep vein thrombosis during or after pregnancy, anticoagulant medication is usually continued for 6 weeks to 3 months after giving birth.^{1, 2}

References

Citations

1. Greer IA (1999). Thrombosis in pregnancy: Maternal and fetal issues. Lancet, 353(9160): 1258–1265.

2. Task Force on Pulmonary Embolism, European Society of Cardiology (2000). Task force report: Guidelines on diagnosis and management of acute pulmonary embolism. European Heart Journal, 21(16): 1301–1336.

3. Ginsberg JS, et al. (2001). Use of antithrombotic agents during pregnancy. Sixth ACCP Consensus Conference on Antithrombotic Therapy. Chest, 119(1, Suppl): 122S–131S.

Credits

Last updated:	January 26, 2006
Author:	Ralph Poore
Reviewed By:	Kathleen Romito, MD - Family Medicine, Jeffrey S. Ginsberg, MD - Hematology
Editors:	Susan Van Houten, RN, BSN, MBA, Terrina Vail