Elena V. Kuklina, MD, PhD, a CDC epidemiologist, and colleagues compared stroke rates during pregnancy, during childbirth, and after childbirth. They used a national database that included discharge information from 1,000 hospitals.
The researchers compared the pregnancy-related stroke rates in the years 1994-1995 and 2006-2007.
"What we found was there was approximately a 50% increase in all stroke," she says. Pregnancy-related strokes totaled about 4,000 in 1994-1995, or about 2,000 each year. In 2006-2007, they totaled about 6,000, or 3,000 annually.
The number of deliveries in the two periods was comparable, she says.
Kuklina says rising rates of high blood pressure, as well as other factors, are to blame.
The study is published in Stroke: Journal of the American Heart Association.
Stroke During Pregnancy, After Pregnancy
Kuklina also looked separately at the three different time periods: during pregnancy, during childbirth, and immediately after childbirth. Compared to the earlier years, she found a 47% increase in stroke during pregnancy and an 83% increase after childbirth. The rate during delivery did not change.
Younger pregnant women -- those 25 to 34 -- were most likely to be hospitalized for stroke, she found.
''We have a population of pregnant women who have a higher risk of having stroke now compared to 10 years ago," she tells WebMD.
Each year in the U.S., about 795,000 people suffer a new or recurrent stroke, according to the American Heart Association.
The researchers looked at all types of strokes, including those caused by clots and by reduced blood flow. They also looked at so-called mini-strokes or transient ischemic attacks (TIAs), which are considered a warning sign of stroke.
More women hospitalized for stroke had high blood pressure in 2006-2007 than in the first period studied. For instance, nearly 41% of those who had a stroke after delivery had high blood pressure. Having high blood pressure increased the risk of pregnancy-related stroke up to about six times, Kuklina says. Having heart disease boosted the risk of stroke by as much as about 10 times.
Complicating the issue, she says, is that "we know very little about how to treat stroke and high blood pressure during pregnancy."
"There's no consensus on how to treat women with high blood pressure which remains after delivery," Kuklina says.
Expert: Pregnant Women Should Know Risks
The study is an important one, says Cheryl Bushnell, MD, director of the Wake Forest Baptist Stroke Center at the Wake Forest Baptist Medical Center in Winston-Salem, N.C.
She has also studied pregnancy-related stroke. She analyzed the same data in 2000 to 2001, and she notes some differences in what conditions were considered under the stroke "umbrella" for the current study. However, the CDC researchers did compare the same conditions for the two time periods.
In her own research, Bushnell says, she also included migraine and found it associated with stroke.
The study does not focus on ethnicity, and that is a limitation, Bushnell says. "We found that African-American race was independently associated with risk of stroke during pregnancy."
''Women getting pregnant should know what their risk factors are and make sure they understand what a healthy lifestyle entails," she says. "It is just as important for young women to be aware of this as for older women, especially as high blood pressure, diabetes, and obesity are occurring at younger and younger ages."