The researchers found that between 2000 and 2010 there were more than 3,400 diagnoses of venous thrombosis.
For women who did not use any type of hormonal contraceptive, two women developed clots for every 10,000 (combined) years they used contraceptives.
For women taking the pill containing the hormone levonorgestrel, the risk for a clot was three times higher, or 6.2 clots for every 10,000 years they took the pill, the researchers found.
The risk to women who used a skin patch was about eight times higher, or 9.7 clots per 10,000 exposure years.
Women who used a vaginal ring had a 6.5 times higher risk, or 7.8 events per 10,000 exposure years).
For women who used an implant that contained only progestogen, the increased risk for clots was very small. There was no risk for women using a progesterone-only IUD and it may have has a protective effect, the researchers noted.
There was no reduction in risk with the long-term use of a patch or vaginal ring, they added.
"For the majority of young women, the recommendation is second-generation combined pill with levonorgestrel, and for women who have given birth, that a hormone-releasing intrauterine device is an attractive option, because it at the same time does not increase the risk of venous thrombosis, perhaps even protects against them, and reduces menstrual complaints," Lidegaard said.
To cut the number of women who develop clots from these riskier birth control methods, the authors advised that more women choose the pill.
Dr. Elizabeth Poynor, a gynecologist and pelvic surgeon at Lenox Hill Hospital in New York City, commented that "over the past years, newer versions of combined hormonal contraception have been developed."
"While these types of transdermal hormonal contraceptives may be more con
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