Blood clots and pregnancy
A blood clot (also called a thrombosis) is a mass or clump of blood that forms when blood changes from a liquid to a solid.
The body normally makes blood clots to stop the bleeding after a scrape or cut. But sometimes blood clots can partly or completely block the flow of blood in a blood vessel, like a vein or artery. This can cause damage to body organs and even death.
Most women with blood clotting conditions have healthy pregnancies. But these conditions may cause problems for some pregnant women. In severe cases, they can cause death for both mom and baby. But testing and treatment can help save both you and your baby.
If you’re pregnant or trying to get pregnant and have had problems with blood clots in the past, tell your health care provider at a preconception checkup (before pregnancy) or at your first prenatal care checkup. Also tell your provider if someone in your family (your parent or a brother or sister) has had problems with blood clots. This means the condition may be in your family history (run in your family).
If you or someone in your family has had problems with blood clots, talk to your provider about getting a blood test to see if you have a thrombophilia. This is a health condition that increases your chances of making abnormal blood clots. Some pregnant women with thrombophilias need treatment with medicines called blood thinners. They stop clots from getting bigger and prevent new clots from forming.
Who is at risk for having blood clots?
Certain things make you more likely than others to have a blood clot. These are called risk factors. Having a risk factor doesn’t mean for sure that you’ll have a blood clot. But it may increase your chances. Talk to your health provider about what you can do to help reduce your risk.
Risk factors for blood clots include:
- Being pregnant. Your blood clots more easily during pregnancy to help your body get ready to lessen blood loss during labor and birth. Also, blood flow in your legs gets slower late in pregnancy. This is because the blood vessels around your pelvis and other places are more compressed (narrow) and your growing uterus (womb) puts pressure on your pelvis.
- Having certain health conditions, like a thrombophilia, disseminated intravascular coagulation (also called DIC), high blood pressure, diabetes or being overweight or obese. DIC causes blood clots to form in small blood vessels and can lead to serious bleeding. Certain pregnancy and childbirth complications (like placenta accreta), surgery, sepsis (blood infection) and cancer can cause DIC. A family history of blood clotting problems also increases your chances of blood clots.
- Taking certain medicines, like birth control pills or estrogen hormones. These medicines can increase the risk of clotting. If you’ve had problems with blood clots or thrombophilias or have a family history of these conditions, birth control pills may not be safe for you to use. Talk to your health care provider about other birth control options.
- Smoking. Smoking damages the lining of blood vessels, which can cause blood clots to form.
- Having surgery, like a cesarean section (also called c-section). A c-section is a surgery in which your baby is born through a cut that your doctor makes in your belly and uterus. The American College of Obstetricians and Gynecologists (ACOG) recommends that doctors help prevent blood clots in women during a c-section. This may include using compression devices that put pressure on your legs to help keep your blood flowing during the c-section.
- Being dehydrated. This means you don’t have enough water in your body. Dehydration causes blood vessels to narrow and your blood to thicken, which makes you more likely to have blood clots.
- Not moving around much. This may be because you’re on bed rest during pregnancy or recovering from surgery or an accident. Being still for long periods of time can lead to poor blood flow, which makes you more likely to have blood clots. Even sitting for long periods of time, like when travelling by car or plane, can increase your chances of having a blood clot.
- Having a baby. You’re more likely to have a blood clot in the first 6 weeks after birth than women who haven’t given birth recently.
What problems can blood clots cause during pregnancy?
If you have a blood clot or a kind of thrombophilia called antiphospholipid syndrome (also called APS), you may be more likely to have complications that can affect your health and your baby’s health, including:
Blood clots in the placenta. The placenta grows in your uterus (womb) and supplies the baby with food and oxygen through the umbilical cord. A blood clot in the placenta can stop blood flow to your baby and harm your baby.
Heart attack. This usually happens when a blood clot blocks blood and oxygen flow to the heart. Without blood and oxygen, the heart can’t pump blood well, and the affected heart muscle can die. A heart attack can lead to lasting heart damage or death.
Intauterine growth restriction (also called IUGR). This is when your baby grows poorly in the womb.
Miscarriage. A miscarriage is when a baby dies in the womb before 20 weeks of pregnancy.
Placental insufficiency. This is when the placenta doesn’t work as well as it should so your baby gets less food and oxygen.
Preeclampsia. Preeclampsia is a condition that can happen after the 20th week of pregnancy or right after pregnancy. It’s when a pregnant woman has high blood pressure and signs that some of her organs, like her kidneys and liver, may not be working properly. Some of these signs include having protein in the urine, changes in vision and severe headache.
Premature birth. This is when your baby is born before 37 weeks of pregnancy.
Pulmonary embolism (also called PE). An embolism is a blood clot that moves from where it formed to another place in the body. When the clot moves to a lung, it’s a PE. PE can cause low oxygen levels in your blood and damage your body organs. It’s an emergency and a leading cause of death during pregnancy. Signs and symptoms of PE may include:
- Trouble breathing
- Fast or irregular heartbeat
- Chest pain
- Feeling anxious
- Coughing up blood
Stillbirth. This is when a baby dies in the womb after 20 weeks of pregnancy.
Stroke. This happens when a blood clot blocks a blood vessel that brings blood to the brain, or when a blood vessel in the brain bursts open. Pregnancy and childbirth cause strokes in about 8 in 100,000 women. Stroke can cause lasting damage to the body or death.
Thrombosis. This happens when a blood clot forms in a blood vessel and blocks blood flow. It most often happens in the deep veins of the legs but can be in other places of the body:
- Cerebral vein thrombosis (also called CVT). This happens when a blood clot forms in a vein in the brain. CVT can lead to stroke. Signs and symptoms include headache, vision problems and seizures.
- Deep vein thrombosis (also called DVT). This happens when a blood clot forms in a vein deep in the body, usually in the lower leg or thigh. DVT can be diagnosed with ultrasound or other imaging tests. Signs and symptoms may include warmth and tenderness over the vein and pain, swelling or skin redness in the affected area.
Venous thromboembolism (also called VTE). This happens when a blood clot breaks off and travels through blood to vital organs, like the brain, lungs or heart. This condition includes DVT and PE. VTEs that block blood vessels in the brain or heart can cause stroke or heart attack.
How are these conditions treated?
Your provider may use tests like ultrasound or magnetic resonance imaging (also called MRI) to find out if you have a blot clot or clotting conditions. Ultrasound uses sound waves and a computer screen to show a picture of your baby inside the womb. MRI is a medical test that makes a detailed picture of the inside of your body. These tests are painless and safe for you and your baby.
If you’re pregnant and have a clotting condition, you may need to go for prenatal care checkups more often than women who don’t have these blood clot conditions. At these visits, your provider checks your blood pressure and can use other tests, like blood tests, to monitor your health.
Your provider also checks your baby’s health in the womb using tests like:
- Ultrasound to check your baby’s growth and development. She may use a special kind of ultrasound called Doppler to check your baby’s blood flow in the umbilical artery, a blood vessel in the umbilical cord. The umbilical cord connects your baby to the placenta. It carries food and oxygen from the placenta to the baby.
- Fetal heart rate monitoring (also called a nonstress test or NST). This test checks your baby’s heart rate in the womb and sees how the heart rate changes when your baby moves. Your provider uses this test to make sure your baby’s getting enough oxygen.
During pregnancy your provider may give you a blood thinner called heparin (low-molecular weight heparin or unfractionated heparin). Your provider also may refer you to a hematologist. This is a doctor who treats blood conditions.
After you give birth, your provider may continue to treat you with heparin. Or he may treat you with a blood thinner called warfarin. Warfarin is safe to take after pregnancy, even if you’re breastfeeding. Warfarin is not safe to take during pregnancy because it may cause birth defects.
Last reviewed: February, 2015