Pregnancy Increases Stroke Risk in Younger, But Not Older, Women

Pregnancy is a major risk factor for stroke in younger women, but not in older women.

Younger women, but not older women, are at greater risk of stroke during pregnancy compared with non-pregnant women of the same age, according to a study published in JAMA Neurology.

The incidence of pregnancy-associated stroke, estimated at 34 of every 100,000 pregnancies, is on the rise. More and more women are delaying childbearing, and a relevant concern is that the risk of stroke during pregnancy may be increased among older women. However, whether the risk of stroke among pregnant older women is higher than the stroke risk among non-pregnant older women has not been extensively explored.

“Pregnant women are usually excluded from trials, and we are just beginning to explore the pathophysiology of pregnancy-associated stroke, which may be quite different from other kinds of strokes,” study author Eliza Miller, MD, of Columbia University, told Neurology Advisor.

In a retrospective cohort study, Dr Miller and colleagues used billing data from a New York State Department of Health database to evaluate the risk of stroke in pregnant and non-pregnant women stratified by age group.

Of 19,146 women hospitalized with stroke, 797 (4.2%) were pregnant or post-partum. The incidence of pregnancy-related stroke (per 100,000 deliveries) was 14, 21.2, 33, and 46.9 for age groups 12 to 24 years, 25 to 34 years, 35 to 44 years, and 45 to 55 years, respectively.

Compared with non-pregnant counterparts, pregnant women in the youngest age group had the highest risk of stroke, which progressively decreased with older age: incidence risk ratios were 2.2, 1.6, 1.1, and 0.6 for women aged 12 to 24 years, 25 to 34 years, 35 to 44 years, and 45 to 55 years, respectively.

Nearly 1 out of 5 strokes in women younger than 35 years were associated with pregnancy, compared with only 1.4% of strokes in women 35 years or older.

“While pregnancy-associated stroke is more common in older women than in younger women, it has a disproportionate effect on younger women,” Dr Miller said.

Pregnancy appeared to be a major risk factor for stroke among younger women but not among older women. But according to Dr Miller, “comparing women over 35 who are pregnant to non-pregnant women over 35 may be biased, since the population of women over 35 who are pregnant is skewed toward healthier women.” Across all age groups, non-pregnant women with stroke were significantly more likely to have vascular risk factors, including diabetes, chronic hypertension, and active smoking.

The findings of this study may help guide the direction of future research in pregnancy-associated stroke. “Over a third of the women in our study who had pregnancy-associated strokes had preeclampsia or other hypertensive disorders of pregnancy,” Dr Miller noted. “I believe that this is a clue that can lead us down the right path as we investigate the causes of pregnancy-associated stroke.”

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Miller EC, Gatollari HJ, Too G, Boehme AK, Leffert L, Elkind MS, Willey JZ. Risk of Pregnancy-Associated Stroke Across Age Groups in New York State. JAMA Neurol. 2016 Oct 24. doi: 10.1001/jamaneurol.2016.3774.