Two new studies add to the growing evidence that birth control pills containing a newer type of progestin may put some women at higher risk for blood clots.
Both studies, published today in the British Medical Journal, found that women who took pills containing drospirenone -- which includes the brands Yasmin, Yaz and Ocella -- more than doubled their risk of nonfatal blood clots when compared with those who took pills containing levonorgestrel, an older form of progestin, included in the brands Levlite or Levlen.
But the overall risk for blood clots with any birth control pill -- whether it contains drospirenone or levonorgestrel -- remains low, said Dr. Lauren Streicher, an assistant professor of obstetrics and gynecology at the Feinberg School of Medicine at Northwestern University.
"While there may be an increase in blood clots, it's important to keep in mind that the likelihood of developing a blood clot is so low in a low-risk population that a two- to three-fold increase may not translate to large absolute numbers," said Streicher.
Women who are pregnant are at higher risk for blood clots than women who are on the pill -- a blood clot occurs in one pregnant woman for every 1,000 to 1,500 pregnant women, while one in 3,000 women who take birth control pills experience some form of blood clot, according to the National Blood Clot Alliance.