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Birth Control Health Center

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Which Birth Control Pill Is Safest?

Researchers Find Differences in Blood Clot Risk in Different Oral Contraceptives

Birth Control Pills and Blood Clots continued...

The risk of blood clots was also associated with the level of estrogen in the pills, with higher estrogen dose linked with higher risk.

In the national Danish study, researchers evaluated the risk of blood clots among healthy Danish women, ages 15 to 49, who were using various types of birth control pills from 1995 to 2005.

During that period, they observed 4,213 blood clots.

The risk decreased with duration of use and decreasing dose of estrogen. Like the Dutch researchers, the Danish team found that pills with levonorgestrel had a lower risk of blood clots than pills that contain other types of progestins. They found pills with norethisterone to be lower risk, too.

Second Opinion

The new research confirms previous findings and adds new information, says Ricardo Azziz, MD, chairman of obstetrics and gynecology at Cedars-Sinai Medical Center in Los Angeles, who reviewed the data for WebMD.

"We know that the combination pills [with estrogen and a progestin] do increase the risk of thrombosis," he says. It's also known, he says, that women with an inherited clotting disorder are at higher risk for having a clot if they take the pill.

But, he adds, overall ''the chances of any woman taking birth control pills having a deep vein thrombosis is low. Of 10,000 women using the pill, in one year's time six will have a deep vein thrombosis."

What's also known, he says, is "the longer you use it the less chance of having a DVT." That might be due to what experts call "selection bias" -- women who had a problem discontinued using the pill and those who remain on it are simply less prone to blood clotting problems.

What is also important to understand, Azziz says, is that even if the risk of blood clots from one type of pill is twice or more that of another, "We are talking about twice the risk for something that is quite rare to begin with."

Women shouldn't go off the pill based solely on the new findings, he says. What is crucial, he says, is for a woman's doctor to prescribe the birth control pill that's best for her, the one that will be linked with the least side effects. "Some patients will do better on some pills than others," he says.

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