SAN ANTONIO, TX — February 7, 2002 — The first major study of ischemic stroke in women taking the latest form of low-oestrogen birth control pills finds that they still have about double the stroke risk than women not taking the pill.
These findings were reported today at the American Stroke Association's 27th International Stroke Conference (ISC). The American Stroke Association is a division of the American Heart Association.
In absolute terms, the number of women likely to have stroke from taking "the pill" rises from about three to six women per 10,000 a year, say the Dutch researchers.
Ischemic stroke is caused by insufficient blood flow to the brain, most commonly due to a blood clot that blocks circulation.
Oral contraceptives (OCs) are a mixture of synthetic female hormones. First-generation birth control pills, introduced in the 1960s, contained very high doses of oestrogens and the progestogens lynestrenol or norethisterone. These pills were associated with an increased risk of blood clots, known as thrombotic events. Blood clots can travel to the heart, causing a heart attack, or to the brain, causing a stroke.
In the early 1970s, second-generation birth control pills were developed with the intent to reduce thrombotic events. They contain low oestrogen (less than 50 micrograms) and the progestogen levonorgestrel.
A decade later, third-generation OCs were developed to try to decrease side effects associated with the progestogens in the second-generation preparations — such as weight gain, acne and adverse changes in cholesterol levels. Third-generation formulations also contained less estrogen than first-generation compounds but combined them with different progestogens: desogestrel or gestodene.
Previous studies of second-generation OCs found an increased stroke risk particularly among smokers and women with high blood pressure. There is limited data on third-generation pills. In the current study, researchers assessed the risk of ischemic stroke with the three generations of oral contraceptives. Of the 203 stroke cases and 925 controls between the ages of 18 and 49, they found the risk of stroke in women taking any type of OC to be 2.3 times that of women not taking one.
The few women still using the first-generation pill were 1.7 times more likely to have a stroke than women not using any oral birth control. Women taking the third-generation pill had an increased stroke risk 2.2 times that of non-pill users. Those taking the second-generation pill formulations had 2.4 times the risk, says senior author Ale Algra, M.D., associate professor of clinical epidemiology at University Medical Center, Utrecht, the Netherlands.
Risk factors for stroke — smoking, hypertension, diabetes and high cholesterol — appeared to add to the stroke risk in all pill users in the study.
"Because there is virtually no difference in the risk of stroke in second- and third-generation pills, the balance of the decision whether to use second- or third-generation oral contraceptives should be determined by the risk of venous thrombosis, blood clots deep in the leg," Dr. Algra says.
Last year, Dr. Algra and his team linked third-generation OCs with an increased risk of developing blood clots in deep veins of the body (venous thrombosis). In a meta-analysis of previous studies of OCs, the group found a higher risk of venous thrombosis in third-generation pills than of second-generation pills. Venous thrombosis usually resolves without complications, but the clots can travel to the lungs, causing a life-threatening pulmonary embolism.
Because of the risk of leg blood clots with third-generation OCs, Dr. Algra suggests women use second-generation OCs. Very few women take the first-generation version of the pill.
"They seriously should consider using second-generation preparations if they did not use OCs before, or switching from third-generation pills to second-generation pills if they are current users," he stresses.
In the Netherlands, about 43 percent of all women of childbearing age use OCs, with about 40 percent of them (about 17 percent of all women) taking third-generation preparations.
Figures from the National Center for Health Statistics show that 17 percent of American women age 15 to 44 were using the pill in 1995. The data did not differentiate formulations of OCs.
Recently, the same research group published data indicating women taking third-generation OCs might have a lower risk for heart attack than women on second-generation pills, but the data was inconclusive. Women are advised to talk to their physician about the risks and benefits of oral contraceptives.
SOURCE: American Heart Association