New Birth Control Pills, Same Old Stroke Risk

Feb. 7, 2002 -- Hopes that the latest generation of birth control pills would put women at less risk of stroke than older formulations were shattered today by research presented at a meeting of stroke experts.

"Women using any type of birth control pills have about twice the stroke risk of nonusers," senior researcher Ale Algra, MD, associate professor of clinical epidemiology at the University Medical Center in Utrecht, the Netherlands, tells WebMD. "We found no difference in stroke risk between the second- and third-generation birth control pills."

"This was a very carefully done study that reiterates our concerns about stroke risk going back to the first generation of birth control pills," Robert Adams, MD, Regents Professor of Neurology at the Medical College of Georgia in Augusta, tells WebMD.

"The hope was that changing the chemical composition of the birth control pill would avoid the increased stroke risk, but this study shows that there is still a small but real risk," says Adams, who was not involved in the study.

Birth control pills contain synthetic female hormones including estrogen, which prevents pregnancy by interfering with egg release. Unfortunately, estrogen also increases the risk of blood clots, which cause strokes when they develop in the brain.

In hopes of reducing this risk, second-generation birth control pills -- developed in the early 1970s -- contained a much lower dose of estrogen than the first-generation birth control pills introduced in the 1960s.

But women using these pills soon noticed unpleasant side effects, including weight gain, acne, and increased cholesterol, which doctors related to other female hormones, called progestins, contained in the pills.

To cut back on these side effects, third-generation birth control pills developed a decade later also contained low amounts of estrogen, but used different progestins.

Algra's study is the first to compare the three generations of birth control pills. The team looked specifically at the risk of stroke caused by insufficient blood flow to the brain -- usually due to a blood clot that blocks circulation. They studied 203 women who had a stroke between the ages of 18 and 49, and compared them with 925 women of similar age who had not had a stroke.

Stroke risk in women using any type of birth control pills was double that of nonusers -- about six strokes per 10,000 women per year, compared with only three strokes in women not on the pill.

Twice the risk sounds like a lot, but the risk of a stroke is still not that great because women of child-bearing age are at fairly low risk of stroke in general, Adams says, adding that most earlier studies have come up with similar results.

The few women still using the first-generation pill were 1.7 times more likely to have a stroke than nonusers. Surprisingly, risk of stroke was even higher with the newer pills -- 2.2 times that of non-pill users for the third-generation pill and 2.4 times the risk for the second-generation pill.

Other risk factors for stroke, including smoking, high blood pressure, diabetes, and high cholesterol, increased stroke risk in all pill users.

"Additional risk factors for stroke add considerably to the risk imposed by birth control pills," Adams says. "Women with these conditions should consider other forms of birth control, or should reduce stroke risk by other means, like stopping smoking or losing weight."

"Women with high blood pressure, high cholesterol, or diabetes should work with their doctor to reduce these risks," Algra agrees.

In an earlier study, Algra's group found that relative to second-generation pills, newer forms of the pill increased risk of developing blood clots in deep veins of the legs. If the clots travel to the lungs, they can choke off the blood supply there, causing death.

"Women taking birth control pills for the first time should start with second-generation pills, and if they are using third-generation pills now, they should consider switching to second-generation to avoid blood clots deep in the leg," Algra says.

Because every woman is different in risk factors for stroke and in personal preferences regarding birth control, the experts recommend talking with your doctor about the risks and benefits of different birth control pills or alternative methods of preventing pregnancy.