The risk of pregnancy-associated stroke is much greater in young women, but not older women, according to a new study by researchers at Columbia University Medical Center (CUMC) and NewYork-Presbyterian.
So although the risk of stroke generally increases with age, the researchers found that pregnancy significantly increases this risk in young women. In older pregnant women, however, the risk of stroke is approximately the same, whether they are expecting or not.
Pregnancy-associated stroke occurs in approximately 34 in 100,000 women. Prior research had suggested that this risk is higher in older women than in younger women, particularly since more women are waiting until later to become pregnant.
“The incidence of pregnancy-associated strokes is rising, and that could be explained by the fact that more women are delaying childbearing until they are older, when the overall risk of stroke is higher,” said Joshua Z. Willey, M.D., assistant professor of neurology at CUMC, assistant attending neurologist on the stroke service at NewYork-Presbyterian/Columbia, and a senior author on the paper.
“However, very few studies have compared the incidence of stroke in pregnant and non-pregnant women who are the same age.”
The findings are published in the journal JAMA Neurology.
For the study, the research team looked at data showing every woman who had been hospitalized for stroke in New York State between 2003 and 2012. Out of a total of 19,146 women, aged 12 to 55 years, 797 (4.2 percent) were pregnant or had just given birth.
The researchers found that the overall incidence of stroke during or soon after pregnancy increased with age: 46.9 in 100,000 in women (aged 45 to 55) vs 14 in 100,000 in women (aged 12 to 24).
However, pregnant and postpartum women in the youngest group (age 12 to 24) had more than double the risk of stroke than non-pregnant women in the same age group: 14 in 100,000 in pregnant women vs 6.4 in non-pregnant women).
For women aged 25 to 34, pregnancy increased the risk 1.6 times. Stroke risk was similar in pregnant and non-pregnant women in the older age groups.
“We have been warning older women that pregnancy may increase their risk of stroke, but this study shows that their stroke risk appears similar to women of the same age who are not pregnant,” said Eliza C. Miller, M.D., a vascular neurology fellow in the Department of Neurology at CUMC and NewYork-Presbyterian and lead author of the study.
“But in women under 35, pregnancy significantly increased the risk of stroke. In fact, one in five strokes in women from that age group were related to pregnancy. We need more research to better understand the causes of pregnancy-associated stroke, so that we can identify young women at the highest risk and prevent these devastating events.”
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