Women's Health Specialists of St. Louis
Obstetrics and Gynecology

Articles - Thrombophilia

The only truly life threatening risk in taking birth control pills or other hormonal contraception is the risk of the development of blood clots. Thankfully, a serious blood clot only occurs in approximately 20 out of 100,000 women who use hormonal contraception. In the past, when clotting events occurred, women were simply told not to take birth control and no further evaluation or instruction was given. We now know that it is likely that all women who have a blood clot while on hormonal contraception, actually have an underlying blood clotting disorder. Blood clotting disorders or thrombophilias are inherited disorders which cause women to form blood clots more readily than the average woman. Though hormonal contraception raises the risk some, the even greater elevation of hormones during pregnancy raises the risk even higher. The presence of a blood clotting disorder however, does not guarantee that a blood clot will occur, it only increases the risk. For example, the most common blood clotting disorder in the United States is thought to be Factor V Leiden. This is also sometimes called Activated Protein C Resistance. Approximately 10% of the population in the United States is thought to have one copy of the gene that causes this blood clotting disorder. Having one copy of the gene will result in some increase in the risk of forming a blood clot. If a woman inherits two copies of the gene, the risk of developing a blood clot is greatly increased. The risk is estimated to be increased somewhere between 1-25% depending on other factors. These factors include the presence of other blood clotting disorders, pregnancy, other medical illnesses, etc. Though blood clotting disorders may be present in 10% of the population, thankfully the risk of developing a blood clot in pregnancy occurs only in about 60 per 100,000 women. Unfortunately, the development of a blood clot is the leading cause of death during pregnancy. It is also a common cause of recurrent miscarriage, severe pre-eclampsia and other complications with pregnancy.

Women who have experienced a blood clot on birth control pills should receive further evaluation if contemplating pregnancy as they will be a greatest risk for development of a blood clot when they are pregnant. The risks to both mother and baby may be reduced or avoided with proper identification and management of a blood clotting disorder. There are many other disorders other than Factor V Leiden. Though most clotting disorders require treatment with a blood thinning medication, there is one disorder that may be treated with supplemental vitamins.

Menopause is another time when women may be at increased risk because of an underlying blood clotting disorder. More commonly, many women are inappropriately denied all options of hormonal replacement therapy because of a personal or family history of blood clots even though no formal evaluation has been performed. Evaluation of a blood clotting disorder is often not offered because of the expense of the multiple tests that must be performed. These tests should be considered for women with histories of three or more spontaneous miscarriages, certain pregnancy complications, and women with a history of a blood clot. Prolonged immobilization as is the case after a broken leg can result in the formation of a blood clot even in people without a blood clotting disorder. Women with a history of a blood clot should always share that information with their health care provider.