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 Women taking any combined oral contraceptive pills - containing both
estrogen and progestin - were three times as likely to develop a
blood clot in a deep vein in the leg or pelvis, compared to women
not on the Pill. The risk was higher still with all the newer Pill
versions except one, researchers found.
“This association is between 1.5 and 1.8 times higher for the newer
formulations,” said lead author Yana Vinogradova, a research fellow
in medical statistics at the University of Nottingham.
The blood clots, known as venous thromboembolisms (VTEs), are common
and can be deadly if the clot dislodges and travels to the heart,
brain or lungs. They are more common among women taking estrogen
medicines, and the risk is even higher if the woman smokes,
according to the National Library of Medicine.
But the overall risk of a blood clot for women on any combined oral
contraceptives is still relatively low: between six and 14 extra
cases per year per 10,000 women taking the drugs, Vinogradova told
Reuters Health by email.
Newer combined pills, including the progestins drospirenone,
desogestrel, gestodene or cyproterone acetate, have been suspected
of carrying an even higher clot risk compared to older versions that
include levonorgestrel and norethisterone. But most past studies
have been small or flawed by not taking into account certain other
risk factors for clots, the study team writes in BMJ.
To assess VTE risk in women on both older and newer-generation
pills, the researchers analyzed U.K. general practice databases
covering the period between 2001 and 2013. They found 5,062 cases of
VTE among women ages 15 to 49, and matched each of these women with
up to five women who did not have a blood clot in the same year, but
were of similar age and treated at a similar medical practice.
The researchers accounted for smoking, alcohol consumption, race,
body mass index and other health problems, and found that women
taking any combined oral contraceptive were almost three times as
likely to suffer a blood clot as those not taking contraceptive
pills.
Women taking older-generation drugs were about 2.5 times as likely
to have a blood clot as women not taking any oral contraceptives
over the previous year. Those taking newer types of combined pills
were about four times as likely to suffer a clot compared to women
not taking oral contraceptives.
The exception among the newer formulations was norgestimate, with a
risk profile more similar to the older drugs.
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The results would translate to a number of “extra” cases of VTE
among women taking the combined pills versus women not on the Pill.
These numbers were lowest for the older drug levonorgestrel and the
newer norgestimate, with an additional six cases per 10,000 women
per year, and highest for two newer drugs, desogestrel and
cyproterone, with an extra 14 cases each.
“However,” Vinogradova noted, "these increased risks of (venous
thromboembolism) associated with both the older and the newer pills
are lower than those associated with pregnancy,” which may increase
clot risk tenfold.
The newer pills carry higher clot risk, but were introduced as
potentially having new benefits as well, including reduced acne,
headache, depression, weight-gain, breast symptoms and breakthrough
bleeding, she said.
The association between different oral contraceptives and blood clot
risk has been controversial and previous study results have been
mixed, but the new findings help to clarify those inconsistencies,
Susan Jick, a professor at Boston University School of Public Health
wrote in an editorial accompanying the new results.
About nine percent of women worldwide take birth control pills,
including 28 percent of women in the U.K., the authors write.
Any women who are concerned should discuss treatment options with
their doctor at their next routine appointment, Vinogradova said.
“Some women are at higher risk of (blood clot) because of family
history or other medical conditions and doctors will already take
account of these factors when advising women regarding their options
for contraception,” she said.
SOURCE: http://bit.ly/1HLEsMQ and http://bit.ly/1J5rnj7 The BMJ,
online May 26, 2015.
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