The proportion of pregnant women who experience a rare type of stroke has increased, researchers reported Wednesday at the American Stroke Association’s International Stroke Conference.

Overall, the risk of having a stroke during pregnancy is small, with about 34 strokes occurring for every 100,000 deliveries.

Spontaneous subarachnoid hemorrhage, or sSAH, is a rare type of stroke that occurs when the blood vessels on the surface of the brain rupture, causing bleeding into the space between the brain and the skull.

The study analyzed data from 2002 to 2014 in the Nationwide Inpatient Sample, the largest public database on hospital stays in the U.S. During that time, 73,692 women between the ages of 15 to 49 were admitted for an sSAH; 3,978, or 5.4 percent, were pregnant. During the 12-year study period, the proportion of pregnant women experiencing an sSAH increased from 4 percent to 6 percent.

Women in their 20s and African-American women were mostly likely to have an sSAH during pregnancy, the researchers found.

“We need to increase awareness in the medical community about the increasing trend of spontaneous subarachnoid hemorrhage in pregnancy,” Dr. Kaustubh Limaye, a clinical assistant professor in the Division of Cerebrovascular Diseases at the University of Iowa in Iowa City said in a news release.

Among women who had an sSAH, those who were pregnant fared better. Eight percent of pregnant women with sSAH admitted to the hospital died, compared to 17 percent of non-pregnant women. Pregnant women also were more likely to go home from the hospital rather than be admitted to another medical facility.

The database did not provide information about stroke severity, and some cases may have been incorrectly classified as a stroke, the researchers said.

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