A new study suggests that the birth control patch and ring may have a higher risk of deep venous thrombosis (blood clots) than birth control pills. Danish researchers published the results of their 10 year study May 10 in the British Medical Journal.
Hormonally active contraceptives carry a risk of deep venous thrombosis. According to UCLA Health System, deep venous mainly affects the large veins in the lower leg and thigh. The clot can block blood flow and cause swelling and pain. When a clot breaks off and moves through the bloodstream, this is called an embolism. An embolism can lodge in the brain, lungs, heart, or other area, leading to severe damage.
Researchers at the University of Copenhagen followed 1,628,158 non-pregnant women aged 15 through 49 who had no history of venous thrombosis or cancer. They were followed from 2001 through 2010. The investigators evaluated the incidence of venous thrombosis in users of the following types of hormonal contraception: transdermal (skin patches), vaginal (i.e., vaginal ring), intrauterine (i.e., IUD), or subcutaneous implant (contraceptive material placed beneath the skin; i.e., Norplant). They calculated the relative risk of venous thrombosis compared with non-users; in addition, they calculated the risk in current users of non-oral products compared with a standard reference oral contraceptive (levonorgestrel and 30-40 µg estrogen). The diagnosis of venous thrombosis was confirmed by the need for at least four weeks of anticoagulation therapy after the initial diagnosis.
The researchers found that within 9,429,128 woman-years of observation, 5,287 first-ever venous thromboses occurred; 3,434 were confirmed by the aforementioned criterion. For woman who did not take hormonal contraception the rate of confirmed venous thrombosis cases was 2.1 per 10,000 woman years. Compared with non-users of hormonal contraception, the relative risk of confirmed venous thrombosis in users of transdermal combined contraceptive patches was 7.9; the relative risk for users of the vaginal ring was 6.5. The corresponding incidences per 10,000 exposure years were 9.7 events for the transdermal patch and 7.8 events for the vaginal ring. The relative risk was increased in women who used subcutaneous implants (1.4); however, it was not increased in women who used the levonorgestrel intrauterine system (IUD; 0.6). Compared with users of combined oral contraceptives containing levonorgestrel, the adjusted relative risk of venous thrombosis in users of transdermal patches was 2.3 for the transdermal patch and 1.9 for the vaginal ring.
The authors concluded that women who use transdermal patches or vaginal rings for contraception have a 7.9 and 6.5 times increased risk of a venous thrombosis compared with non-users of hormonal contraception of the same age, corresponding to 9.7 and 7.8 events per 10,000 exposure years. The risk was slightly increased in women using subcutaneous implants; however, not in those using the levonorgestrel intrauterine system.
Take home message:
The authors noted that data regarding smoking was not available; however, they stated that smoking was a “weak risk factor” in young women. Smokers have an increased risk of venous thrombosis even if they do not use a hormonal contraceptive. However, smokers who use a hormonal contraceptive have a significantly higher risk of venous thrombosis; thus, if a woman cannot quit smoking, she should not take a hormonal contraceptive. A woman must bear in mind that pregnancy has a higher risk of venous thrombosis as well as other adverse events than a woman who is taking a hormonal contraceptive. A common reason for a pregnancy occurring while taking oral contraceptives is missing some pills during the cycle. Both the patch and the vaginal ring have a distinct advantage in that regard. The patch is applied weekly for three weeks, followed by one week without the patch. A woman inserts the ring in her vagina herself. It stays in the vagina for three weeks. At the end of the third week, she removes the ring for one week.