Contraceptive Rings and Patches Raise Clot Risk

Women who use certain types of non-oral hormonal contraception such as rings or patches are at much greater risk for developing venous thrombosis, claims a new study.

Researchers at the University of Copenhagen (Denmark) conducted an historical Danish national registry based cohort study to assess the risk of venous thrombosis in current users of non-oral hormonal contraception. The participants were all Danish nonpregnant women aged 15-49 (a total of 1,626,158 women), free of previous thrombotic disease or cancer, and followed from 2001 to 2010. The main outcome measures was the incidence rate of venous thrombosis in users of transdermal, vaginal, intrauterine, or subcutaneous hormonal contraception, relative risk of venous thrombosis compared with nonusers, and rate ratios of venous thrombosis in current users of non-oral products compared with the standard reference oral contraceptives.

The results showed that with women who used transdermal combined patches had an almost eight times higher risk of thrombosis; those using vaginal rings had 6.5 times the risk. In all, during 9,429,128 person-years of follow-up, there were 5,287 cases of venous thrombosis, for a rate of 8.1 per 10,000 person-years. The rate among women not using any hormonal contraception was 2.1 per 10,000 person-years. The relative risk rose to 3.2 among women on oral contraceptives containing 30 to 40 µg estrogen and levonorgestrel. The study was published on May 10, 2012, in BMJ.

“These data could be interpreted as meaning that in order to prevent a single venous thrombosis during the course of a year, 1,250 women using the patch and 2,000 using the ring would have to switch to oral combined contraceptives,” concluded lead author Ojvind Lidegaard, MD, and colleagues.

A transdermal, combined contraceptive is a patch applied to the skin that releases synthetic estrogen and progestin hormones to prevent pregnancy. They have been shown to be as effective as the combined oral contraceptive pill with perfect use, and the patch may be more effective in typical use. The patch works primarily by preventing ovulation; a secondary mechanism of action is inhibition of sperm penetration by changes in the cervical mucus.

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