Updated December 30, 2014.

When your blood clots, a lot of proteins in your body work together to make that happen. One of those proteins is called Factor V. Factor V Leiden is a genetic variation of Factor V that affects the blood-clotting process and makes a person more likely to form blood clots.

A person can have one copy of the Factor V Leiden gene and one normal copy (meaning the person is heterozygous), or a person can have two copies of the Factor V Leiden gene (the person is homozygous).

Protein C Resistance:

The Factor V Leiden gene is also associated with a condition called activated protein C resistance. Protein C is another protein involved in the clotting process. The majority of people with activated protein C resistance also have the Factor V Leiden genetic variation.

Statistics:

About 4% to 7% of the population is heterozygous for Factor V Leiden. Around 0.06% to 0.25% of the population is homozygous for Factor V Leiden. Different ethnic groups have different rates of the Factor V Leiden mutation; it is most common in people from northern Europe.

Risks:

Factor V Leiden means an increased risk of deep vein thrombosis and medically important blood clots. Some studies have found that having the Factor V Leiden mutation means an increased risk of recurrent miscarriages, possibly because of tiny blood clots blocking the flow of nutrients to the placenta.

Treatment:

In pregnancy, some doctors believe in using heparin and/or low-dose aspirin to treat women who have the Factor V Leiden gene and a history of miscarriages.

Currently, researchers are still studying this treatment to verify that it actually helps.

Relationship of Factor V Leiden to Miscarriages:

Researchers are still studying the exact nature of the relationship between Factor V Leiden (and other hereditary thrombophilias) and recurrent miscarriages. Different genetic blood clotting disorders have different levels of relationship to miscarriage, but Factor V Leiden is one of the hereditary thrombophilias that does appear to have a role in causing miscarriages (or at least increasing risk), because women with the mutation have a higher rate of miscarriages than women without it.

Available research suggests that Factor V Leiden can play a role in miscarriages that happen after 10 weeks but it is less likely to be a factor in early miscarriages.

Many doctors do test for Factor V Leiden as a part of the recurrent miscarriage workup of tests and recommend treatment for those who test positive.

<sub>Sources:

Coulam, C.B., R.S. Jeyendran, L.A. Fishel, and R. Roussev, "Multiple thrombophilic gene mutations rather than specific gene mutations are risk factors for recurrent miscarriage." American Journal of Reproductive Immunology May 2006. Accessed 9 Mar 2008.

Foka, Z.J., A.F. Lambropoulos, H. Saravelos, G.B. Karas, A. Karavida, T. Agorastos, V. Zournatzi, P.E. Makris, J. Bontis, and A. Kotsis, "Factor V leiden and prothrombin G20210A mutations, but not methylenetetrahydrofolate reductase C677T, are associated with recurrent miscarriages." Feb 2000. Accessed 9 Mar 2008.

Jivraj, S., R. Rai, J. Underwood, and L. Regan, "Genetic thrombophilic mutations among couples with recurrent miscarriage." Human Reproduction May 2006. Accessed 9 Mar 2008.

Reznikoff-Etievan, M.F., V. Cayol, B. Carbonne, A. Robert, F. Coulet, and J. Milliez, "Factor V Leiden and G20210A prothrombin mutations are risk factors for very early recurrent miscarriage.' BJOG Dec 2001. Accessed 9 Mar 2008.

University of Illinois - Urbana/Champaign, "Patient Resources: Factor V Leiden." Hematology Resource Page. Accessed 9 Mar 2008.

Walker, M.C., S.E. Ferguson, and V.M. Allen, "Heparin for pregnant women with acquired or inherited thrombophilias." The Cochrane Library 21 Jan 2003. Accessed 9 Mar 2003.</sub>