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Study finds increased risk of blood clots with transdermal patch and vaginal ring contraceptives

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Women using a transdermal patch or vaginal ring contraceptives are at greater risk of blood clots than those taking certain oral contraceptives, according to a new study.

Between 2001 and 2012, researchers used national registries in Denmark to follow all Danish women aged 15-49 who were not pregnant and had no history of previous thrombotic disease or cancer. They compared the rate of venous thrombosis in women using no hormonal birth control to rates in women using one of several kinds of non-oral hormonal contraceptives.

The non-oral contraceptive products compared in the study included:

  • Transdermal patches containing norelgestromin and ethinylestradiol (such as Ortho Evra)
  • Vaginal ring with etonogestrel (third generation progestogen) and ethinylestradiol (such as NuvaRing)
  • Subcutaneous implants containing etonogestrel only (such as Implanon)
  • Levonorgestrel intrauterine system IUD (such as Mirena)

The study assessed two reference oral contraceptives with levonorgestrel and norgestimate for comparison.

A venous thrombosis is a blood clot that forms in a vein. In cases of deep vein thrombosis where a blood clot forms in a vein deep in the body such as the thigh, the blood clog can break off and travel through the bloodstream. If it blocks an artery of the lungs, it can cause a life-threatening condition called a pulmonary embolism.

Women taking oral contraceptives with oestrogen and levonorgestrel were 3 times more likely to develop venous thrombosis than women using no hormonal birth control. While use of the transdermal patch was associated with 7.9 times the risk and the vaginal ring 6.5 times the risk.

Researchers saw only a small increased risk of venous thrombosis in woman using the subcutaneous implants. They noted that use of the levonorgestrel IUD actually decreased the risks.

Researchers advised women to use combined oral contraceptives with levonorgestrel or norgestimate, rather than transdermal patches or vaginal rings.

The study Venous thrombosis in users of non-oral hormonal contraception: follow-up study, Denmark 2001-10 appears in the May 10, 2012 issue of the journal BMJ.

“The transdermal patch and vaginal ring confer at least a six fold increased risk of venous thrombosis as combined pills with desogestrel or drospirenone, a risk which is about twice the risk among women using second-generation pills with levonorgestrel,” lead researcher Dr. Ojvind Lidegaard, a professor of obstetrics and gynecology at the University of Copenhagen, told HealthDay News. “Women should be informed about these risks in order to be able to choose the most appropriate hormonal contraceptive product. There are hormonal contraceptive alternatives which confer less or no risk of venous thrombosis.”

Women should be aware that different types of progestin in oral contraceptives might carry different risks of venous thrombosis. The U.S. Food and Drug Administration (FDA) says some studies have shown the risk of blood clots associated with birth control pills containing drospirenone may be 1.5 to 2 times higher than those containing levonorgestrel. Brands of oral contraceptives containing drospirenone include Yaz, Yasmin, Ocella, Safyral, Syeda, Zarah, Beyaz, Gianvi and Loryna.