Non-oral contraception confers increased thrombosis risk
MedWire News: Women who use non-oral hormonal contraception have a greater risk for venous thrombosis than those who do not, a study in BMJ shows.
Øjvind Lidegaard (University of Copenhagen, Denmark) and team found that the risk for venous thrombosis was slightly increased in women who used subcutaneous implants compared with those who used levenorgestrel intrauterine systems.
Previous studies have assessed the risk for venous thrombosis in women using oral contraceptive pills, but few have assessed the risk in those using non-oral hormonal contraceptives.
Lidegaard and team reviewed data on contraceptive use and first-ever venous thrombosis in 1,626,158 Danish nonpregnant women aged 15-49 years between 2001 and 2010. None of the women had a history of blood clots or cancer before the study began.
Over 9,429,128 woman-years of observation, 3434 confirmed diagnoses of first-ever venous thrombosis events were recorded. The incidence rate of confirmed venous thrombosis events was 2.1 per 10,000 woman-years.
In analyses adjusted for age, calendar year, and education, women who used transdermal combined contraceptive patches were 7.9 times more likely to experience venous thrombosis, than those who did not use hormonal contraception. The incidence in this group was 9.7 events per 10,000 exposure years.
Women who used the vaginal ring were also 6.5 times more likely to experience thrombosis than those who did not use hormonal contraception. The incidence in this group was 7.8 events per 10,000 exposure years.
Women who used subcutaneous implants were a significant 1.4 times more likely than nonusers of hormonal contraception to have venous thrombosis. However, there was no significant difference in risk between women who used the levenorgestrel intrauterine system and those who did not use hormonal contraception.
Women who used transdermal patches were 2.3 times more likely, and those who used the vaginal ring 1.9 times more likely, to have venous thrombosis than those who took a combined oral contraceptive pill containing levonorgestrel.
After stratification according to length of use, the relative risk for venous thrombosis in women who used combined oral contraceptives was reduced with increasing length of use, from 4.25 at less than 1 year after starting use, to 2.71 at over 4 years after use.
The authors say that their findings indicate that women should use combined oral contraceptives containing levonorgestrel or norgestimate rather than transdermal patches or vaginal rings.
In fact, if 2000 women who currently use a vaginal ring and 1250 women who use a transdermal patch switch to a combined oral contraceptive containing levenorgestrel, one event of venous thrombosis would be prevented in a year, they estimate.
MedWire (www.medwire-news.md) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2012
By Piriya Mahendra