Thrombophilia: A Disorder That Increases the Risk of a Blood Clot During and After Pregnancy

Thrombophilia pregnancy

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You need to form blood clots to prevent bleeding. Without this ability, a simple cut would be deadly. But if you are one of the eight to fifteen percent of Americans with a condition called thrombophilia, you may form clots that you don’t need. The word “thrombus” means clot. These clots usually form inside a vein and they can be dangerous.

Most people with thrombophilia don’t know they have it. They may have the condition, but it is not serious enough to form abnormal blood clots. Pregnancy is a condition that increases blood clotting normally. This is nature’s way of preventing too much bleeding during and after childbirth. Because pregnancy adds additional clotting ability, it may cause a woman with thrombophilia to start forming abnormal blood clots.

Knowing about thrombophilia is important, but it is also important to know that the overall risk for a dangerous blood clot during pregnancy is very low. Only one or two pregnancies out of one thousand have complications from blood clots.

What Is Thrombophilia?

Thrombophilia is a group of disorders that cause abnormal blood clots. Eighty percent of these clots form inside veins. A common area for blood clots is a vein of the leg or pelvis. The formation of a clot is a complicated process that involves blood cells called platelets and proteins called clotting factors.

There are two main types of thrombophilia:

  • One type is inherited thrombophilia. This type is passed down through genes that run in families. The most common of these is called factor V Leiden. Factor V Leiden affects about five to seven percent of white Americans of European descent. It is less common in other races.
  • The second type is acquired thrombophilia. The most common is a disorder called antiphospholipid syndrome (APS). People with APS form antibodies that attack the inside linings of blood vessels. This causes damage that leads to clotting. A disorder in which antibodies attack the body is called an autoimmune disease. About five to seven percent of pregnant women may have APS.

Thombophilias and Pregnancy

Because pregnancy increases your ability to clot by a factor of four to five times normal, pregnancy may increase the risk of thrombophilia significantly. Pregnancy also increases your risk of clotting because the growth of your belly slows down blood flow through the veins of your legs and pelvis. Slow blood flow – called stasis – makes it easier for your body to form clots.

Some thombophilias are more dangerous than others during pregnancy. APS thrombophilia has been linked to these pregnancy problems:

  • Slow growth of the baby (intrauterine growth restriction)
  • Poor blood flow through the placenta (placental insufficiency)
  • High blood pressure during pregnancy (preeclampsia)
  • Premature birth
  • Loss of the pregnancy (miscarriage or stillbirth)

Inherited types of thombophilias are not as strongly linked to these pregnancy problems as acquired causes. They are considered lower risk for pregnancy.

Are You at Risk?

Since many people with a thrombophilia have never had a problem from a blood clot, you may not know you are at risk. You may be at risk if you have:

  • A family history of abnormal blood clots (parent or sibling)
  • A past history of abnormal blood clots
  • Had three or more miscarriages
  • Had a stillbirth
  • Had preeclampsia that caused a premature birth

You may be at additional increased risk if:

  • You smoke
  • Are overweight
  • Are over age 35
  • Are not staying active
  • Are carrying twins
  • Need a C-section

Signs and Symptoms

One of the most common type of abnormal blood clot forms in a deep vein of the leg. This is called a deep vein thrombosis (DVT). Signs and symptoms of DVT include:

  • Pain in one leg (usually in the calf or behind the knee)
  • Swelling
  • Tenderness
  • Warmth
  • Redness
  • A swollen looking vein

These symptoms deserve immediate attention. You should call your doctor right away or get to emergency care. A blood clot can also form in an area that does not cause symptoms. The first symptoms may be caused by the blood clot breaking away and traveling to your lung or brain. This is called an embolism.

An embolism is a medical emergency. Brain embolism causes headache, vision changes, or seizure. Lung embolism causes difficulty breathing, chest pain, and coughing up blood.

Diagnosis and Treatment

If you have been diagnosed with thrombophilia, or you have a history of DVT, treatment to prevent abnormal blood clots should be discussed at your preconception or first prenatal visit.

If you have risk factors for thrombophilia, your doctor may decide to do a panel of blood tests to diagnose thrombophilia and the cause. If you have risk factors, and your doctor does not ask, tell him or her about them.

Abnormal blood clots may occur during or after pregnancy. The most common times are during the first three months of pregnancy and in the six weeks after delivery. The type of treatment depends on the type of thrombophilia (high or low risk), your history, risk factors, and family history.

Your primary care doctor may add a blood specialist (hematologist) to your treatment team. There are many options for treatment. These include more frequent blood testing and imaging studies to check your health and the health of your baby. For low-risk thrombophilia, this may be the only treatment. For high-risk thrombophilia, medications can be used to prevent blood clots. If a clot does form, there are medications used to dissolve clots before they cause problems.

Bottom Line

The combination of being pregnant and having a thrombophilia can increase your risk of abnormal blood clots during and after pregnancy. The risk of blood clots should be part of your prenatal or preconception discussion with your doctor. The good news is that blood clots can be prevented and treated.

The overall risk for a dangerous blood clot during pregnancy is very low. In addition to working with your doctors on diagnosis and treatment, you can help prevent blood clots by maintain a healthy weight, staying active, and not smoking or being around secondhand smoke.

Christopher Iliades
Dr. Chris Iliades is a medical doctor with 20 years of experience in clinical medicine and clinical research. Chris has been a full time medical writer and journalist since 2004. His byline appears in over 1,000 articles online including EverydayHealth, The Clinical Advisor, and Healthgrades. He has also written for print media including Cruising World Magazine, MD News, and The Johns Hopkins Children's Center Magazine. Chris lives with his wife and close to his three children and four grandchildren in the Boston area.

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