Pregnancy and the Increased Risk of Developing Blood Clots

Pregnancy Blood Clots

Note: The Pregistry website includes expert reports on more than 2000 medications, 300 diseases, and 150 common exposures during pregnancy and lactation. For the topic Blood Clots, go here. For the topic Inherited Platelet Disorders, go here. These expert reports are free of charge and can be saved and shared.


Expecting moms have a 3 to 5 times greater risk of having a blood clot than they did prior to pregnancy. While the chances of having a blood clot are higher, blood clots still only affect about 1 to 2 expecting moms out of every 1000. A blood clot is a mass of solidified blood that normally forms in response to an injury or a cut in your skin to stop the bleeding. Your body normally breaks down and removes the clot after the injury has stopped bleeding and begun to heal. However, pregnancy can result in a state where your blood is more likely to clot. When you deliver your baby, your body is vulnerable to excessive bleeding after the placenta detaches. During pregnancy, your body adapts to prevent this blood loss by making it easier for your blood to clot. This increases the risk for blood clots in expecting moms. The likelihood of blood clots during pregnancy is also increased by changes in your body’s hormones and the growing size of the uterus applying pressure to your veins. Your risk for blood clots is further increased by injury to the veins during delivery or cesarean section and inactivity after the birth of your baby.

What types of blood clots occur during pregnancy?

Most blood clots (75-80%) during pregnancy occur in the deep veins of the legs or pelvis, a condition called deep vein thrombosis (DVT). If you notice that one of your legs is swollen, warm, red, or painful, especially your left leg, you should contact your doctor immediately. This could be a sign of a DVT. The other 20-25% of blood clots that occur are due to a pulmonary embolism (PE). A PE is when a blood clot that formed in the leg or pelvis separates and travels through your blood to your lungs. Once inside the lungs, it gets stuck in a blood vessel and blocks blood flow. Signs of a PE include: shortness of breath, chest pain, coughing up blood, or fast heartbeat. A PE can be life-threatening and must be treated immediately. DVTs must also be treated immediately to ensure that the clot does not permanently damage your blood vessels or separate and develop into a PE.

In addition to the risk for blood clots in your veins, pregnancy also increases the chances of having a blood clot in the arteries. Veins and arteries are both types of blood vessels in your body. Veins carry blood to your heart, and arteries carry blood away from your heart. When a blood clot forms in an artery, it can block blood flow to your heart or brain, resulting in a heart attack or stroke. The risk for blood clots in the arteries during pregnancy is slightly less than for the veins, but these types of clots also result in more deaths in expecting moms and new moms. Blood clots in the arteries are less common, occurring in only about 20% of expecting moms or new moms, while blood clots in the veins occur in about 80%. Clots can also harm your baby by forming inside of the placenta and preventing your baby from receiving blood flow.

When can I expect my risk to return to normal?

The risk for blood clots is highest after you deliver your baby. The first week after delivery has a 100 times higher risk of blood clots than prior to pregnancy, and the first 6 weeks after the birth of your baby have a 20 to 80 times greater risk. It is unclear when moms will return to their pre-pregnancy state and no longer be at a higher risk for blood clots, but the risk continues to be double 7-12 weeks after delivery. Expecting moms are also more likely to have a blood clot throughout all trimesters of pregnancy compared to prior to pregnancy, especially during the third trimester.

How can I tell if I am at a higher risk for blood clots during pregnancy?

There are many factors that can raise your chances of having a blood clot during pregnancy. These include the following:


If you are pregnant or have recently delivered your baby, you have a greater risk for developing a blood clot. It is important to tell your doctor about your medical history, especially if you think that you have factors that increase your chances of having a blood clot. You can also ask your doctor about what types of exercises are recommended and safe during and after pregnancy. Incorporating some light exercise into your lifestyle and avoiding sitting for long periods of time will improve blood flow in your legs and throughout your body to help prevent blood clots.

Brittani Zurek
Dr. Brittani Zurek earned her Doctor of Pharmacy from the University at Buffalo School of Pharmacy and Pharmaceutical Sciences. She currently works as a medical writer, specializing in disease management and medication therapy. Brittani also writes continuing education modules for healthcare professionals. She enjoys hiking and spending time outdoors in her free time.

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