Newer birth control pills and blood clot controversy

April 22, 2011 2:54:17 PM PDT
It has long been known that taking birth control pills slightly increase a woman's chance of having a blood clot. But do some pills have an even higher risk?

Researchers are looking at some new evidence to answer that question.

Women who use birth control pills containing the newer type of progestin, drospirenone (such as Yaz and Yasmin), may have almost twice the risk of developing a blood clot as those taking pills with the hormone that has been used for decades, levonorgestrel, according to two studies published online in the British Medical Journal.

Both studies, one done in the U.S. and the other in the U.K., found an increased risk of blood clots among women taking the newer progestin, compared to levonorgestrel, the older and most commonly prescribed progestin.

Previous studies on this topic have shown inconclusive results, with half showing a slight increased risk and half showing no risk. These studies have also come under heat because they analyzed all cases of blood clots, regardless of the presence of underlying risk factors or potential causes of the clots.

The most recent studies did try to exclude cases with certain risk factors, such as recent surgery or cancer, but they did not account for two very important ones- smoking and a family history of clots.

In the U.S. study, researchers used a medical claims database to find women who were currently taking birth control pills with either drospirenone or levonorgestrel and those who experienced a blood clot.

Among the women with clots, 65% of them were taking pills containing pills with drospirenone.

Interestingly, women under 30 appeared to be at the greatest risk. These young women were found to have almost 4 times the risk of having a blood clot if they took drospirenone pills.

However, doctors advise caution when looking at these results.

Pregnancy actually puts women at higher risk for blood clots than birth control pills do.

The risk of a blood clot among all women taking birth control pills is about 1 in 3,000. Compare that to the risk of a clot during pregnancy, which is about 1 in 1,000, according to a study in the New England Journal of Medicine.

Birth control pills typically contain two hormones, an estrogen and a progestin. Estrogen is known to increase levels of clotting factors in the body, resulting in a slightly higher risk of clots. However, it is not known how the low doses of progestin found in contraceptive pills may lead to blood clots, nor has it ever been proven.

Experts recommend that you should talk to your doctor before you consider stopping or switching your birth control pill.