Women who have a hormone disorder called polycystic ovary syndrome (PCOS) and who take the birth control pill have twice the risk of blood clots than do other women on the pill, according to a new study.
"For many women with PCOS, (the risks) will be small," said Dr. Christopher McCartney, an associate professor at the University of Virginia School of Medicine in Charlottesville, who was not involved in the new work. "For some women, they might be high enough to say we really shouldn't use the pill, such as for women over 35 who smoke."
The three to five percent of women in the U.S. with PCOS have a hormone imbalance, which can lead to irregular periods, extra hair growth and higher risks for being overweight and developing hypertension and diabetes.
They are often treated with oral contraceptives, many of whose labels already include warnings about blood clots. A blood clot, also called venous thromboembolism, can be deadly if it spreads to the lungs, although none of the cases of blood clots in the study were fatal.
Because women with PCOS already tend to have more heart disease risk factors, researchers wanted to see if the pill adds any additional risk.
They used medical and pharmacy information from a large health insurance database, including 43,500 women with PCOS.
On average, over the course of a particular year, about 24 out of every 10,000 women with PCOS taking the pill were diagnosed with a blood clot, compared to about 11 out of every 10,000 women without the disorder using the contraceptive.
"Am I particularly surprised by the findings? No," said Dr. Shahla Nader-Eftekhari, a professor at the University of Texas Medical School at Houston, who treats women with PCOS but was not involved in the current study.
Obesity playing a role?
The study, published in the Canadian Medical Association Journal, could not say for sure why women with PCOS are more likely to have a blood clot.
McCartney said he suspects that obesity has something to do with it.
At the beginning of the study in 2001 the percent of women with and without PCOS who were obese was the same - about 13 percent - but by the end of the study in 2009, 33 percent of women with PCOS and 21 percent of women without the disorder were obese.
"I really think that could be something that's contributing to the risk," McCartney told Reuters Health.
"Weight not only contributes to the risks associated with the pill, it also contributes to some of the symptoms of PCOS and some of the metabolic problems associated with PCOS," he added.
McCartney pointed out that the risk of developing a blood clot, even among women with PCOS, is still considered small, and shouldn't necessarily discourage women from taking the pill.
Steven Bird, the lead author of the study and an epidemiologist with the U.S. Food and Drug Administration, said that the importance of the findings is to raise awareness among women and their doctors that there is an increased risk for them if they take the pill.
"Although the risk is small, prescribers should consider the increased risk for blood clots in women with PCOS who are prescribed contraceptive therapy," Bird told Reuters Health by email.
McCartney agreed, and added that it's also a good reminder for doctors of women with PCOS to discuss the importance of maintaining a healthy weight.