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Thromboembolic Disorders During Pregnancy

By Lara A. Friel, MD, PhD, Associate Professor, Maternal-Fetal Medicine Division, Department of Obstetrics, Gynecology, and Reproductive Sciences, University of Texas Health Medical School at Houston, McGovern Medical School

In thromboembolic disorders, blood clots (thrombi) form in blood vessels. An embolus is a blood clot that travels through the bloodstream and blocks an artery. In the United States, thromboembolic disorders are a common cause of death in pregnant women.

The risk of developing a thromboembolic disorder is increased for about 6 weeks after delivery. Most complications due to blood clots result from injuries that occur during delivery. The risk is much higher after cesarean delivery than after vaginal delivery.

Blood clots usually form in the superficial veins of the legs as thrombophlebitis or in the deep veins of the legs as deep vein thrombosis. Symptoms can include leg swelling, pain, and tenderness. These symptoms may be hard to recognize because pregnancy can cause similar symptoms. The severity of the symptoms does not correlate with the severity of the disease.

Deep vein thrombosis may also develop in the pelvis. There, it may not cause symptoms. A clot can move from the deep veins of the legs or pelvis to the lungs. There, the clot may block one or more lung (pulmonary) arteries. This blockage, called pulmonary embolism, can be life threatening.


  • Doppler ultrasonography to check for blood clots in the legs

  • Computed tomography to check for pulmonary embolism

During pregnancy, if women have symptoms suggesting a blood clot, Doppler ultrasonography (used to evaluate blood flow) may be done to check the legs for clots.

If pulmonary embolism is suspected, computed tomography (CT) may be done to confirm the diagnosis. CT is done after a radiopaque contrast agent (which can be seen on x-rays) is injected. The contrast agent flows through blood vessels and outlines them. This procedure is called CT angiography. It is relatively safe during pregnancy.

If the diagnosis of pulmonary embolism is still uncertain, a procedure called pulmonary angiography (angiography of the lung's blood vessels) is required. For this procedure, doctors make a small incision, typically in the groin but sometimes in the arm. Then they insert a thin, flexible tube (catheter) and thread it through blood vessels to an artery in a lung. When the catheter is in place, a substance that can be seen on x-rays (called a radiopaque contrast agent) is injected through the catheter to outline the blood vessels in the lungs, and x-rays are taken.

After the baby is delivered, doctors may use CT with a contrast agent to check women for blood clots in the pelvis.


  • Heparin during pregnancy

  • Warfarin after delivery

If a blood clot is detected, heparin (an anticoagulant, a drug that inhibits blood clotting) is started without delay. Heparin may be injected into a vein (intravenously) or under the skin (subcutaneously). Heparin does not cross the placenta and cannot harm the fetus. Treatment is continued for 3 to 6 months. Then, to prevent new blood clots from forming, doctors give the woman heparin at a lower dose for at least 6 weeks after delivery. During this time, the risk of blood clots remains high.

After delivery, warfarin may be used instead of heparin, particularly if women require treatment for more than 6 to 8 weeks. Warfarin can be taken by mouth, has a lower risk of complications than heparin, and can be taken by women who are breastfeeding.

Women who have had a blood clot during a previous pregnancy or who had a thromboembolic disorder before they became pregnant may be given heparin during each pregnancy and for 6 weeks after delivery to prevent blood clots from forming.

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