In the U.S., two-thirds of people with Alzheimer’s disease are women, according to the Alzheimer’s Association. For decades, experts have explained the gender divide by the fact that women also tend to live longer than men, and the biggest risk factor for Alzheimer’s is age.

“Everyone brushed it off to the fact that women were living longer,” says Rachel Whitmer, professor of epidemiology at University of California Davis. “Now science is saying, wait, that’s not the end of the story.”

Pregnancy, according to two of the latest studies on the issue, may have something to do with it.

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