Thrombophilias are health conditions that increase your chances of making abnormal blood clots. 

A blood clot (also called a thrombosis) is a 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. 

If you have a thrombophilia, your body may make extra clots in your blood vessels. This can cause health problems during pregnancy. About 1 in 5 people (20 percent) in the United States has a thrombophilia. 

Most women with thrombophilias have healthy pregnancies. But thrombophilias may cause problems for some pregnant women. In severe cases, they can cause death for both mom and baby. This is why it’s important to learn about thrombophilias. If you’re at risk of having a thrombophilia, testing and treatment can help save both you and your baby.

If you’re pregnant or trying to get pregnant and you know you have a thrombophilia, 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 (a parent, brother or sister) has a thrombophilia or other clotting problems. This means that thrombophilias may be in your family history (run in your family). If you have a family history of these conditions, talk to your provider to see if you need a blood test to check for a thrombophilia.

What problems can thrombophilias cause in pregnancy?

If you have a certain kind of thrombophilia called antiphospholipid syndrome (also called APS), you may be more likely to have pregnancy complications, including:

  • Intrauterine growth restriction (also called IUGR). This is when your baby grows poorly in the womb.
  • Placental insufficiency. The placenta grows in your uterus (womb) and supplies the baby with food and oxygen through the umbilical cord. Placental insufficiency means the placenta doesn’t work as well as it should so your baby gets less food and oxygen.
  • Preeclampsia. This 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.
  • Miscarriage.  A miscarriage is when a baby dies in the womb before 20 weeks of pregnancy.
  • Stillbirth. This is when a baby dies in the womb after 20 weeks of pregnancy.

APS is an acquired thrombophilia. This means it’s not inherited but develops on its own. Researchers are trying to find out if inherited thrombophilias may lead to the same kinds of pregnancy complications.   

Who is at risk for having a thrombophilia? 

Some pregnancy complications may make it more likely for a woman to have a thrombophilia. For example, you may be at risk for a thrombophilia if you’ve had:

  • Three or more miscarriages before 10 weeks of pregnancy and the cause is unknown; or if you’ve had a miscarriage after 10 weeks of pregnancy and the cause is unknown
  • A stillbirth
  • One or more babies born before 34 weeks of pregnancy because of eclampsia (seizures during pregnancy), severe preeclampsia or a problem with the placenta 
  • A thrombosis or you develop one during pregnancy

If you’ve had any of these complications, talk to your provider to see if you need to get tested for a thrombophilia. Treatment before and during pregnancy can help you have a healthy pregnancy and a healthy baby. 

How do you know if you have a thrombophilia?

There are different kinds of blood tests for different thrombophilias. If you’ve had blood clotting problems or if you have a family history of thrombophilias, talk to your provider to see if you need to get tested for an inherited thrombophilia. 

Most people with a thrombophilia have no signs or symptoms. The first sign may be that you develop a health condition related to a blood clot, including:

  • 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 kind of thrombosis happens when a blood clot forms in a vein in the brain. Signs and symptoms include a headache that doesn’t go away, vision problems and seizures.
  • Deep vein thrombosis (also called DVT). This kind of thrombosis happens when a blood clot forms in a vein deep in the body, usually in the lower leg or thigh. Signs and symptoms include warmth and tenderness over the vein and pain, swelling or skin redness in the area of the clot.
  • 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, fainting, feeling anxious or coughing up blood.
  • Venous thromboembolism (also called VTE). This happens when a blood clot breaks off and travels through blood to major 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.

Your provider may use ultrasound or tests like magnetic resonance imaging (also called MRI) to see if you have these conditions. Ultrasound uses sound waves and a computer screen to make a picture of a baby in 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.

How are thrombophilias treated?

Treatment depends on:

  • The type of thrombophilia you have
  • If you’ve had a blood clot in the past
  • Your family history

Your provider may refer you to a hematologist if you don’t already have one. This is a doctor who treats blood conditions.

Some women may need treatment with medicine called blood thinners. Blood thinners stop clots from getting bigger and prevent new clots from forming. You may need this treatment if you’ve had a VTE before or you have a high-risk thrombophilia. You may get a blood thinner called heparin (low-molecular weight heparin or unfractionated heparin). If you have APS and have had miscarriages, your provider may give you low-dose aspirin and heparin to help prevent another miscarriage. 

During pregnancy, you may need to go for prenatal care checkups more often than women who don’t have a thrombophilia. At these visits, your provider checks your blood pressure and can use other tests, like blood tests, to monitor your condition. 

Your provider also may use these tests to check your baby’s health in the womb:

  • Ultrasound. An ultrasound is a prenatal test that uses sound waves and a computer screen to show a picture of your baby inside the womb. She may use a special kind of ultrasound called Doppler ultrasound 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 how the heart rate changes when your baby moves. Your provider uses this test to make sure your baby’s getting enough oxygen. 

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.

You may use birth control after pregnancy to help keep you from getting pregnant again. But some kinds of birth control, like the pill, may increase your risk of having blood clots and not be safe for you to use. If you have a thrombophilia or blood clotting problems or if you have a family history of these conditions, talk to your provider about other birth control options.

What causes thrombophilias?

You have a thrombophilia if your body makes either too much of certain proteins or too little of other proteins that help make clots. 

An acquired thrombophilia is not inherited but develops on its own. The most common acquired thrombophilia is APS. APS is an autoimmune disorder similar to lupus. When you have an autoimmune disorder, antibodies (cells in your body that fight off infections) attack healthy tissue by mistake. If you have APS, your body makes antibodies that attack certain fats that line the blood vessels. This can sometimes cause blood clots. APS happens in up to 5 in 100 (5 percent) pregnant women. 

When a thrombophilia is inherited, it’s passed from parent to child through changes (also called mutations) in genes. A gene is a part of your body’s cells that stores instructions for the way your body grows and works. Changes in certain genes make it more likely for you to have a thrombophilia. These changes include: 

  • Factor V Leiden thrombophilia
  • Prothrombin thrombophilia
  • Protein C deficiency
  • Protein S deficiency
  • Antithrombin deficiency

More information

Last reviewed: January, 2014