Risk of Pregnancy-Associated Stroke Across Age Groups in New York State

Key Points

Question  Does pregnancy increase stroke risk in older women of childbearing age?

Findings  In this population-based study in New York State, age-stratified incidence risk ratios were calculated to determine the stroke risk during pregnancy or post partum, compared with stroke risk in similarly aged nonpregnant women. Stroke risk was more than doubled in women aged 12 to 24 years and increased significantly by 60% in women 25 to 34 years during pregnancy or post partum; there was no difference in stroke risk in women 35 years or older.

Meaning  Pregnancy does not increase stroke risk in older women but does increase stroke risk in younger women.

Abstract

Importance  Older age is associated with increased risk of pregnancy-associated stroke (PAS). Data are limited on age-specific incidence ratios of PAS compared with stroke risk in nonpregnant women.

Objectives  To assess the risk of stroke by age group in pregnant and postpartum women compared with their nonpregnant contemporaries and to compare risk factors across age groups in the exposed (pregnant/postpartum) and unexposed (nonpregnant) populations.

Design, Setting, and Participants  International Classification of Diseases, Ninth Revision, billing codes from the calendar year 2003-2012 New York State Department of Health inpatient database and population data were used to identify all women aged 12 to 55 years with cerebrovascular events, including transient ischemic attack, ischemic and hemorrhagic stroke, cerebral venous thrombosis, and nonspecified PAS. The cumulative incidence of PAS per 100 000 pregnant/postpartum women vs nonpregnancy-associated stroke (NPAS) per 100 000 women in age cohorts of 24 years or younger, 25 to 34, 35 to 44, and 45 years or older was calculated. Risk factors between groups were compared using logistic regression models. The study included data from calendar years 2003 through 2012. Data analysis was performed from July 11, 2015, to July 16, 2016.

Exposures  Pregnancy, including the postpartum period up to 6 weeks after delivery.

Main Outcomes and Measures  Incidence risk ratios (IRRs) for stroke per age cohort, defined as cumulative risk of stroke in the exposed population divided by cumulative risk of stroke in the unexposed population, were determined, and stroke risk factors and mortality were compared between populations.

Results  There were 19 146 women hospitalized with stroke during the study period; 797 of the women were pregnant/post partum. The overall median (interquartile range) age of the women was 31 (25-35) years in those with PAS and 48 (41-52) years in those with NPAS. The incidence of PAS in women aged 12 to 24 years was 14 events per 100 000 pregnant/postpartum women vs NPAS incidence of 6.4 per 100 000 nonpregnant women (IRR, 2.2; 95% CI, 1.9-2.6); for ages 25 to 34 years, 21.2 per 100 000 vs 13.5 per 100 000 (IRR, 1.6; 95% CI, 1.4-1.7); for ages 35 to 44 years, 33 per 100 000 vs 31 per 100 000 (IRR, 1.1; 95% CI, 0.9-1.2); and for ages 45 to 55 years, 46.9 per 100 000 vs 73.7 per 100 000 (IRR, 0.6; 95% CI, 0.3-1.4). PAS accounted for 18% of strokes in women younger than 35 years vs 1.4% of strokes in women aged 35 to 55 years. Women in the NPAS group vs the PAS group had more vascular risk factors, including chronic hypertension (age <35 years: 437 [15.7%] vs 60 [9.8%], P < .001; age 35-55 years: 7573 [48.6%] vs 36 [19.3%], P < .001), diabetes (age <35 years: 103 [3.7%] vs 9 [1.5%], P = .002; age 35-55 years: 2618 [16.8%] vs 12 [6.4%], P < .001), and active smoking (age <35 years: 315 [11.3%] vs 29 [4.8%], P < .001; age 35-55 years: 2789 [17.9%] vs 10 [5.3%], P < .001); and had higher mortality (age <35 years: 288 [11.3%] vs 37 [6.5%], P < .001; age 35-55 years: 2121 [13.4%] vs 14 [6.1%], P < .001).

Conclusions and Relevance  Younger women, but not older women, have an increased stroke risk during pregnancy and post partum compared with their nonpregnant contemporaries. These results suggest that pregnancy does not increase the risk of stroke in older women.

JAMA Neurology 2016