In the United States, thromboembolic disorders are the leading cause of death in pregnant women. In thromboembolic disorders, blood clots form in blood vessels. They may travel through the bloodstream and block an artery. The risk of developing a thromboembolic disorder is increased for about 6 to 8 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 as deep vein thrombosis. Symptoms include swelling, pain in the calves, and tenderness. 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 arteries. This blockage, called pulmonary embolism, can be life threatening.
Diagnosis and Treatment
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—see Pulmonary Embolism (PE): Diagnosis) may be done to confirm the diagnosis. CT is relatively safe during pregnancy. If the diagnosis of pulmonary embolism is still uncertain, a procedure called pulmonary angiography is required.
If a blood clot is detected, heparin (an anticoagulant) 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 6 to 8 weeks after delivery, when the risk of blood clots is high. After delivery, warfarin may be used instead of heparin. 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 may be given heparin (an anticoagulant) during subsequent pregnancies to prevent blood clots from forming.
Last full review/revision December 2008 by Sean C. Blackwell, MD