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.