Certain non-oral hormonal contraceptives, such as skin patches, implants and vaginal rings, have been found to increase the risk of
serious blood clots, venous thromboembolism, according to a study published in
The findings suggest that some women should switch from a
non-oral product to a contraceptive pill to help reduce their risk.
Several studies have assessed the risk of venous thrombosis
(a collective term for deep vein thrombosis and pulmonary embolism) in women
using oral contraceptive pills, but few studies have assessed the risk in users
of non-oral hormonal contraceptives.
These products more continuously release hormones into the
body to prevent pregnancy.
A team, led by Professor Řjvind Lidegaard at the University
of Copenhagen, reviewed data on non-oral hormonal contraceptive use and first
ever venous thrombosis in all Danish non-pregnant women aged between 15 and 49
years from 2001 to 2010. All the women had no record of either blood clots or
cancer before the study began.
Several factors that could affect the results, including age
and education level, were taken into account.
The results are based on 9,429,128 observation years during
which 3,434 confirmed diagnoses of first ever venous thrombosis were recorded.
The risk of venous thrombosis among women who did not use
any type of hormonal contraception and who were 15-49 years old was on average
two events per 10,000 exposure years. Women taking a combined oral
contraceptive pill containing the hormone levonorgestrel had a three times
increased risk (6.2 events per 10,000 exposure years).
Compared with non-users of the same age, women who used a
skin patch had an eight times increased risk (9.7 events per 10,000 exposure
years), while women who used a vaginal ring had a 6.5 times increased risk (7.8
events per 10,000 exposure years).
Use of a progestogen-only subcutaneous implant carried a
slightly increased risk, while use of a progestogen-only intrauterine device
did not confer any risk, and may even have a protective effect, say the
Unlike combined pills, no reduction in risk was seen with
long-term use of a patch or a vaginal ring.
Based on these findings, the authors calculated that 2,000
women using a vaginal ring and 1,250 women using a skin patch should shift to a
combined pill containing levonorgestrel to prevent one event of venous
thrombosis in one year.