Women rarely have strokes during pregnancy or shortly after giving birth, but researchers have seen a big jump in such events over the past 12 years, according to a U.S. study published Thursday. A total of 4,085 pregnancy related stroke hospitalizations were documented in the United States in 1994-95, and that number rose 54 percent to 6,293 in 2006-07, said the study in Stroke: Journal of the American Heart Association. \"We were alarmed,\"\" lead author of the study, Elena Kuklina, told AFP. \"We expected to see some increase but we were surprised by the amount,\" said Kuklina, an epidemiologist at the Centers for Disease Control and Prevention\'s Division for Heart Disease and Stroke Prevention in Atlanta, Georgia. While the overall incidence is still low -- just three-quarters of a percent of women in America had a stroke while pregnant or within three months of giving birth in the latest data -- more research is needed to find the cause of the rise, she said.