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.
Kuklina said one factor may be that more women are overweight when they become pregnant, which can add to the likelihood of complications from diabetes and high blood pressure.
"When you're relatively healthy, your stroke risk is not that high," she said.
"Now, more and more women entering pregnancy already have some type of risk factor for stroke, such as obesity, chronic hypertension, diabetes or congenital heart disease," she added.
"Since pregnancy by itself is a risk factor, if you have one of these other stroke risk factors, it doubles the risk."
Kuklina suggested that doctors have little guidance in the area because pregnant women are often excluded from clinical trials due to the potential for drugs to harm the fetus.
The data in the study came from a large national database of five to eight million discharges from 1,000 hospitals.
When she searched for published medical literature on the topic, she found discussions of just 11 cases of pregnancy-related stroke, Kuklina said, urging more and better research on pregnant women.