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Blood clot risk varies with type of hormonal birth control

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Hormonal contraceptives can be administered as pills, intrauterine devices, injections, or implants. In any form, hormonal contraceptives have been reported to increase the risk of the formation of venous thromboembolism (blood clot), which could be fatal. A new study evaluated the risk of various hormonal contraceptives and also noted factors that increase the risk of a blood clot forming. The study was published online on August 4 in the journal Obstetrics & Gynecology by Swedish researchers.

The most common site for a blood clot to form is the calf. It is known as a deep venous thrombosis (DVT). The condition can cause pain and swelling in the leg. It the clot dislodges, it can travel to the lungs and cause a pulmonary embolism, which can be fatal. The researchers conducted a study to evaluate the associations between combined hormonal contraceptives, containing estrogen and progesterone and progesterone-only contraception and risks of venous thromboembolism. They also evaluated this risk among women with genetic factors that increased the risk of a blood clot forming.

The study was conducted from 2003 to 2009 and comprised 948 Swedish women with a venous thromboembolism and 902 control subjects; the patients in both groups ranged in age from 18 to 54 years. The women were interviewed by telephone and underwent blood tests pertaining to clotting risk. The blood clots were documented by imaging studies such as ultrasound. The data was subjected to statistical analysis and was adjusted for smoking, body mass index (BMI), and immobilization.

The investigators found that women who were currently taking combined hormonal contraception had a 5.3-fold increased risk of thromboembolism, Desogestrel combinations had the highest risk: 11.4-fold increased risked. The risk increase for injection of medroxyprogesterone acetate (progesterone) was 2.2-fold. Women who used a combined hormonal contraception with a genetic risk factor for a blood clot, the factor V Leiden mutation, the increased risk was 20.6-fold. Among women who used progesterone-only contraception and carried the factor V Leiden mutation, the increased risk was 5.4-fold.

The authors concluded that risks of venous thromboembolism in association with combined hormonal contraception vary by type of progesterone and independently of BMI and smoking. Thrombosis-increasing genetic factors such as factor V Leiden increase risks of venous thromboembolism in users of combined hormonal contraception. Except for injection of medroxyprogesterone acetate, progesterone-only contraception appeared to be the least thrombogenic hormonal contraception for women carrying genetic clotting risk factors.

Take home message:

Smoking and obesity increase the risk of thromboembolism; thus, smokers should either stop smoking or discontinue hormonal contraception (the former is far more preferable). Blood clotting risk is another reason to go on a diet if you have a weight problem. Sitting with the legs crossed or prolonged sitting (e.g., long plane ride, car trip, or bus ride) increase the risk of a clot forming. Thus, avoid crossing your legs and get up and move around periodically on a plane ride. A blood test can check for genetic mutations that increase clotting risk.