August 10 (HealthDay News) -- Women who suffer from migraines that are accompanied by visual symptoms -- usually called an aura -- are at a slightly increased risk of stroke, especially if they smoke and take oral contraceptives, a new study says.

"This should not be a cause of alarm to women," said lead researcher Dr. Steven Kittner, a professor of neurology at the University of Maryland School of Medicine. "But it is something to take into account and discuss with their physician."

The risk that a young woman with migraines in the 15 to 44 age group will have a stroke might be 20 per 100,000, Kittner said. "That's a very small risk. Even if you increase it to 30 per 100,000, it is still a tiny risk."

But, if the woman smokes and has high blood pressure or diabetes, the risk of stroke will be higher, added Kittner, who's also director of the Maryland Stroke Center.

For the study, Kittner and his colleagues collected data on 386 young women, 15 to 49 years of age, who'd had a stroke. The researchers compared these women with 614 similar women who hadn't had a stroke.

They found that women with migraines with visual symptoms had a 1.5 greater risk of stroke, compared with women with no history of migraine.

However, women who had migraines and used oral contraceptives and smoked had a sevenfold increased risk of stroke, compared with women who had migraines with visual symptoms and didn't smoke or use oral birth control.

The researchers also said that the recent onset of migraines, as well as more frequent migraines and migraines that lasted longer, may play a part in increasing the risk of stroke.

"Migraine with visual symptoms should be considered a weak risk factor for stroke," Kittner said. "You can't do anything about it, but it may influence what other prevention measures one may take," he said.

The findings are published in the September issue of the journal Stroke.

Kittner advised that women who have migraines with visual aura should stop smoking and discuss with their doctor the pros and cons of using oral contraceptives.

One stroke expert said the new study adds to research that had already found that migraines with aura increase the risk of stroke in women.

"Many studies have linked migraine with the risk of stroke," said Dr. Tobias Kurth, an associate epidemiologist at Brigham and Women's Hospital and an assistant professor of medicine at Harvard Medical School. "But this study shows other factors that may increase the risk."

Kurth also advises women with migraines to stop smoking. "It really increases the risk of stroke, especially in combination with oral contraceptives," he said.

Whether treating migraines would lower the risk of stroke isn't known, Kurth said. "It's only speculation that if you treat migraine this risk goes away," he said. "There is no data looking at this question."

SOURCES: Steven Kittner, M.D., M.P.H., professor of neurology at the University of Maryland School of Medicine, and director, Maryland Stroke Center, Baltimore; Tobias Kurth, M.D., Sc.D., associate epidemiologist, Brigham and Women's Hospital, and assistant professor of medicine, Harvard Medical School, Boston; September 2007, Stroke