Oral contraception slightly increases risk of ischemic stroke in women

Oral contraceptives pose a small but significant risk of ischemic stroke in women of reproductive age. However, in women with other stroke risk factors, the odds are significantly higher—and these women should not be prescribed the pill, according to a comprehensive retrospective analysis published in August 2015 in MedLink Neurology.

Beginning in 1962, shortly after oral contraceptives were first introduced, researchers had identified a link with strokes. However, the overall risk and the risk in selected populations had not been defined.

In this study, researchers at Loyola University Medical Center and Loyola University Chicago Stritch School of Medicine, in Maywood, IL, reviewed the published data to determine the risk of stroke associated with different types of oral contraceptives.

“For healthy young women without any stroke risk factors, the risk of stroke associated with oral contraceptives is small and probably outweighed by their benefits,” the researchers wrote.

“However, in women with other stroke risk factors, the risk seems higher and, in most cases, oral contraceptive use should be discouraged,” they added. These risk factors include arterial hypertension, cigarette smoking, and migraine—particularly migraine with aura.

About 4.4 ischemic strokes occur for every 100,000 women of childbearing age, according to a meta-analysis cited in the report. Oral contraceptives increase the risk 1.9 times, which equates to 8.5 strokes per 100,000 women. This is still a small risk, the researchers observed, requiring 24,000 women to take oral contraceptives to cause 1 additional stroke. But for women who smoke and take birth control pills, the risk for stroke could as much as double.

Oral contraceptives do not seem to increase the risk of hemorrhagic stroke in the general population, the researchers noted.

How steroid hormone contraception actually increases the risk of underlying stroke is not well understood, the authors wrote. Several pathophysiological mechanisms have been proposed, particularly the induction of a hypercoagulable state, increased blood pressure, venous thromboembolic disease, and genetic susceptibility.

Adding to the confusion is that formulations have changed considerably over the years, the researchers wrote. Early versions of the pill contained doses of synthetic estrogen as high as 150 mcg. Most birth control pills now contain as little as 20 to 35 mcg, and none contain more than 50 mcg of synthetic estrogen.

The researchers also found that women on hormone replacement therapy (with estrogen alone or combined with progesterone) had a 40% increased risk of ischemic stroke. The higher the dose, the higher the risk. “Progestin-only contraceptives seem preferable for women with a history of cerebrovascular disease,” the authors wrote.