Prothrombin is a protein found in the blood. It’s required for your blood to clot properly. Blood clots are solid clumps of blood made up of platelets and a network of a protein called fibrin. Prothrombin is used by your body to form fibrin.

In rare cases, a change in the genetic code, called a mutation, can cause the body to produce too much prothrombin. If an individual has too much prothrombin, blood clots might form when they aren’t supposed to.

People with this genetic condition have a prothrombin mutation, also called a prothrombin G20210A or a factor II mutation.

Most people with prothrombin mutations will never develop an abnormal blood clot. But women who are pregnant already have a higher risk of getting a clot during and right after pregnancy. If a pregnant woman also has a prothrombin mutation, she will have a higher risk of blood clots.

When a blood clot forms inside a blood vessel like an artery or a vein, it can be dangerous. The clot can break off and travel through the blood into an artery in the lungs, heart, brain, or other organs. It can also cause a miscarriage, stillbirth, and other pregnancy complications. And in some cases blood clots can be fatal.

People who have a prothrombin mutation have an increased risk of developing a deep vein thrombosis, also known as a DVT, which is a blood clot that forms in the deep veins (typically in the legs) or a pulmonary embolism (a clot that travels through the blood to the lungs).

Symptoms of a DVT are pain, swelling, and redness in the affected arm or leg. Symptoms of a pulmonary embolism include:

  • shortness of breath
  • chest pain
  • dizziness
  • cough
  • swelling of the legs

DVT can damage the veins and lead to disability. A pulmonary embolism is a serious condition and can be fatal. If you experience any of these symptoms seek immediate medical attention.

Apart from blood clots, prothrombin mutations are associated with an increased risk of complications during pregnancy. These complications include:

  • pregnancy loss (miscarriage or stillbirth)
  • preeclampsia (increased blood pressure and protein in the urine during pregnancy)
  • slow fetal growth
  • placental abruption (early separation of the placenta from the uterine wall)

However, it’s important to note that the majority of women with prothrombin gene mutations have normal pregnancies.

Your parents each pass down one copy of their genes to you at birth. Therefore, everyone has two prothrombin genes. A random change, or mutation, in this gene can be inherited from one or both parents.

More commonly, a prothrombin mutation is inherited from just one parent, while a normal prothrombin gene is inherited from the other parent. In this case, it’s called a heterozygous prothrombin gene mutation. According to University of Iowa Health Care, people with one copy of this gene have about a five times greater chance of getting a blood clot than someone with two normal copies of the gene.

Rarely, both copies of the mutated prothrombin gene, one from each parent, are passed down. This is called homozygous prothrombin gene mutation and it’s more dangerous. These individuals have up to 50 times higher risk of getting a blood clot.

About 2 percent of the U.S. and European Caucasian population have heterozygous prothrombin mutations. It’s less common in African Americans and people of Asian, African, and Native American descent (less than 1 percent). The condition occurs equally in men and women.

The homozygous type is very rare. It’s estimated to occur in just 0.01 percent of the population, according to a study published in the journal Circulation.

If you’ve had a DVT or pulmonary embolism in the past, you should consider getting tested for the prothrombin mutation. Additionally, you may want to consider testing if:

  • you had a blood clot at a young age
  • you have a history of pregnancy loss or pregnancy complications
  • any one in your immediate family, like your parents, siblings, or children have a history of blood clots or known prothrombin mutation

Prothrombin gene mutation is diagnosed with a blood test. A sample of your blood is sent to a laboratory and the DNA is analyzed to determine if the mutation is present.

If a woman has a prothrombin mutation, she may want to consider having anticoagulation therapy during and right after her pregnancy. In this type of therapy, medications are used during the course of a pregnancy to help thin out the blood and prevent blood clots from forming.

These drugs are called anticoagulants, but are sometimes called blood thinners. They decrease your blood’s ability to clot. They keep existing clots as small as possible while decreasing the chance that you’ll develop more clots.

You may receive an injection of a blood thinner called heparin(or low-molecular-weight heparin) for a few days.Your treatment may then be followed by another injectable type of blood thinner or a blood thinner available in pill form called warfarin (Coumadin). Warfarin is typically only used after giving birth due to potential negative effects on the fetus.

Your doctor might suggest alternative medications that could work better for you. Each offers different benefits and risks, so be sure to follow your doctor’s recommendations and instructions.

Reducing or eliminating risk factors for developing a blood clot is the best way to prevent complications. While some of the risk factors associated with blood clots, like a gene mutation, are not controllable, there are other lifestyle modifications that may help reduce your risk.

Some examples include:

  • Try to lose weight if you’re overweight and maintain a healthy weight.
  • Don’t smoke, and if you do smoke talk with your doctor about quitting.
  • Get up and walk around for a few minutes when you’re traveling for two hours or more or if you sit at a desk for long periods of time at work.
  • Make sure to drink plenty of water.
  • If you’re scheduled to get any type of surgery, be sure to tell your doctor about your prothrombin mutation.
  • Know the warning signs of DVT and PE so that you can take action immediately.
  • Exercise regularly; it’s important to stay physically active during your pregnancy. Immobility is a major factor that can lead to blood clots in the legs.
  • Speak with your doctor about using oral contraceptives containing estrogen before or after a pregnancy. Women with a prothrombin mutation have a 16 times higher risk of developing a DVT when they use birth control pills containing estrogen, according to a study published in the journal Circulation.

Talk to your doctor to see which activities and exercises you can do safely while pregnant. Your doctor may also refer you to a hematologist, a specialist who treats conditions of the blood.