Women who take a newer version of birth control pills have a doubled risk of developing potentially fatal blood clots, according to a new study published in the British medical journal BMJ.
Venous thromboembolism is a serious condition that encompasses both deep vein thrombosis — when a person develops a blood clot in the legs — and pulmonary embolism, in which the clot travels to the lungs and obstructs breathing. VTE is potentially fatal, and the study indicates that women who take combined oral contraceptives with newer progesterone formulations are two times more likely to develop it as opposed to women who take a pill with an older version of the synthetic hormone.
To assess the risks among different birth control pills that contain both estrogen and progesterone, research fellow Yana Vinogradova of the University of Nottingham examined medical records from two large U.K. patient databases to compare birth control prescriptions for women who developed VTE and and women who didn’t. She excluded women who had recently had surgery, been pregnant or were already taking anticoagulants before starting their birth control, as such patients have heightened risk for blood clots regardless of hormonal birth control.
After finding over 10,000 cases of women with VTE and matching them with controls of the same age and other factors, she found that women who took combined birth control with newer progesterone formulations (desogestrel, gestodene, drospirenone and cyproterone) had about two times greater odds of developing blood clots than women who took older birth control formulations with norgestimate, or levonorgestrel and norethisterone.
Women who take any kind of birth control pill are at a slightly higher risk of blood clots, heart attack and stroke. In fact, in the course of this study, researchers found that patients on birth control had a threefold increased risk of developing VTE compared to women who weren’t on any birth control.
It’s important to note that while hormonal birth control increases a woman’s risk of VTE, that risk is still lower than the tenfold risk of VTE that comes with pregnancy. And VTE itself is a rare occurrence. According to Vinogradova’s study, the pills that increased blood clot risk the most (those made with desogestrel and cyproterone) only resulted in 14 extra cases per 10,000 women. The pills associated with the lowest rate of VTE — just 6 extra cases per 10,000 women — were made with levonorgestrel and norgestimate.
“There is no suggestion that women should stop or change their treatment without medical advice since this could have undesirable consequences such as an unplanned pregnancy,” epidemiologist Julia Hippisley-Cox, senior author of the study, wrote in a statement emailed to HuffPost. “Instead, anyone with concerns should discuss alternatives with their [doctor] at their next routine appointment.”
“Combined oral contraceptives remain effective and relatively safe drugs — significantly safer in terms of risk of VTE than either pregnancy terminations or pregnancy itself,” added Vinogradova.
Vinogradova’s study is similar to a 2011 Danish analysis of 4,246 VTE cases that also found the newer version of birth control pills roughly doubled the risk of VTE as compared to older versions of the pill. However, Vinogradova’s study more than doubles the amount of VTE cases analyzed, adjusts the data to account for potential differences caused by body mass index, smoking status, ethnic group and alcohol consumption, and includes an additional four years of data.
“Our findings are not novel –- the size and quality of our study simply make our estimates of the relative VTE risks associated with different drug types more accurate and more reliable,” she concluded.
Roughly four out of five sexually active women have used the birth control pill at least once in their life, according to a 2013 CDC survey.
If you’re on hormonal birth control, the best thing you can do to mitigate your risk of a blood clot is to stop smoking. Alternately, if you are overweight, over 35 years old or have a family history of blood clots, you might want to work with your doctor to find an alternative birth control, advises the U.K.’s National Health Service.
The hormone ingredients of your birth control can be found on the packaging. To learn more about which birth control is best for you, talk to your doctor.