Your Resource for all Things Relating to Factor V Leiden

I'm Pregnant... Should I be tested?

The current recommended testing guidelines relating to Factor V Leiden are as follows:


  • those who have venous thrombosis under the age of 50
  • those who have recurrent venous thrombosis
  • those who have a family history of venous thrombosis
  • female smokers who have suffered myocardial infarction under the age of 50
  • venous thrombosis in pregnant women or those taking oral contraceptives
  • some guidelines include women with recurrent pregnancy loss, unexplained severe preeclampsia, placental abruption as well as intrauterine fetal growth restriction

There are a few situations that are not addressed in the above guidelines that could increase your risk. The guidelines assume that you are in contact with direct family members and are aware of any history of venous blood clots they have experienced. Also, the guidelines do not take into account other major risk factors for blood clots such as hospitalization, surgery, trauma, obesity, smoking, and immobility.

Examining the risks….

Factor V Leiden is the most common genetic cause of primary and recurrent venous thromboembolism in women.

According to the National Institutes of Health, venous thromboembolism is the leading cause of maternal death in the United States.

Pregnancy is a risk factor for deep venous thrombosis, and the risk is further increased if you have a personal or family history of thrombosis or thrombophilia such as Factor V Leiden.

Factor V Leiden is by far the most common inherited thrombophilia in the United States.

The only way to know if you have Factor V Leiden, or know if you have the heterozygous type or the much more serious homozygous type of Factor V Leiden is to get tested.

The increased risk for blood clots caused by pregnancy combined with the increased risk for blood clots caused by Factor V Leiden should be taken very seriously.

Studies are still being done to determine the exact role that Factor V Leiden plays during pregnancy and the weeks following the birth. Some studies have suggested that Factor V Leiden is associated with miscarriage, stillbirth, unexplained fetal loss, preeclampsia, placental abruption, intrauterine fetal growth restriction, and blood clots in the placenta and umbilical cord. Other studies have suggested that the association with Factor V Leiden and these issues is lacking. More research is needed.


Until more is known, almost everyone agrees that when dealing with the increased risk of blood clots associated with pregnancy, knowing you have the Factor V Leiden genetic mutation puts you at an advantage over not knowing. Having that extra knowledge helps your healthcare professional make more informed decisions and gives you more of an awareness about the signs and symptoms of dangerous blood clots BEFORE a serious blood clot develops.


You don’t have to search very far to find very heartbreaking and tragic stories about women who have suffered serious pregnancy complications, only to find out later that an unknown genetic disorder called Factor V Leiden that they unknowingly carried played a role. The importance of the test soon becomes clear after reading their stories.


We feel it is a safe assumption that if a woman knew before or after becoming pregnant that she is at a higher risk of blood clotting because she has the genetic mutation, she would want to take all the necessary precautions before and during her pregnancy in order to have a healthy pregnancy.


Despite the increased risks, women are not systematically tested for Factor V Leiden before they are prescribed oral contraceptives, before or during pregnancy, or before commencing hormone replacement therapy unless they fall within the guidelines above. The only way to be tested is to request the test from your healthcare professional or utilize one of the direct-to-consumer DNA testing kits now available from companies like 23andMe.


If you are considering pregnancy or are already pregnant, we strongly recommend that you ask your healthcare professional or genetic counselor if testing for Factor V Leiden should be considered in your situation.


Knowing you have Factor V Leiden could save your life.


The test to see if you have Factor V Leiden is not intrusive and one that your healthcare professional can perform with a simple blood test.


Ultimately, for those who do not fall within the current testing guidelines and testing is not recommended, deciding whether to be tested for Factor V Leiden is a personal decision.

The American Factor V Leiden Association is working hard to promote public awareness, provide education and be a resource for knowledge.

Our current program initiative on testing is aimed at improving testing guidelines by taking a common sense approach and looking at all variables related to the disorder.

We hope to publish an in-depth position statement on Factor V Leiden testing in the coming months.

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