The rates of U.S. women having strokes during or soon after pregnancy have jumped 54 percent over the past 12 years, according to a new study in the American Heart Association journal Stroke. The study, published on Thursday, found that 6,293 women had pregnancy-related strokes in 2006-07, up from 4,085 in 1994-95.

"We were alarmed," the lead author of the study, Elena Kuklina, told AFP. "We expected to see some increase, but we were surprised by the amount.”

Pregnancy-related stroke rates were highest in the South and lowest in the Northeast.

There are about 4 million births in the United States each year, so strokes are still rare among pregnant women and new mothers. However, the study points out disturbing trends in the health of pregnant women today, the researchers said.

More and more women are entering pregnancy with risk factors for stroke, like chronic hypertension, diabetes, congenital heart disease or obesity. In the United States, about one in five women is obese when she becomes pregnant. Also, women are having children later, and the risk of a stroke rises with age.

“We are dealing with a different population of pregnant women now,” Kuklina told MSNBC’s Today.com.

The study presents “a very, very alarm-raising statistic that we need to take extremely seriously,” Dr. Olajide Williams, a neurologist at Columbia University and Harlem Hospital and an American Stroke Association spokesman told the Associated Press. “We need to be more aggressive in screening these women for these risk factors.”