Summary: A large New York State study found that pregnancy and the postpartum period up to six weeks after delivery are associated with an increased risk of stroke in younger women, while older pregnant women did not show a similar increase compared with nonpregnant women of the same age.
Source: JAMA Neurology
Key finding: Women under age 35 experienced a higher risk of pregnancy-associated stroke (PAS) compared with nonpregnant peers, while pregnant women aged 35 and older did not have a higher stroke risk relative to nonpregnant women in the same age groups.
Researchers led by Eliza C. Miller, M.D., of Columbia University analyzed hospital admission data for stroke across New York State from 2003 through 2012 to compare age-specific stroke incidence among pregnant/postpartum women and nonpregnant women. The analysis used inpatient billing records to identify cerebrovascular events and calculated incidence risk ratios (IRRs) for pregnancy-associated stroke versus nonpregnancy-associated stroke (NPAS) across four age cohorts.
The study identified 19,146 women hospitalized with stroke in the decade-long period; 797 of those patients (4.2 percent) were pregnant or within six weeks postpartum. Median ages differed markedly: the median age for women with PAS was 31 years (interquartile range, 25–35), while the median age for women with NPAS was 48 years (interquartile range, 41–52).
Age-specific incidence rates reported in the study were:
- Ages 12–24: PAS incidence 14.0 per 100,000 pregnant/postpartum women versus NPAS incidence 6.4 per 100,000 nonpregnant women (IRR 2.2; 95% CI, 1.9–2.6).
- Ages 25–34: PAS incidence 21.2 per 100,000 pregnant women versus NPAS incidence 13.5 per 100,000 nonpregnant women (IRR 1.6; 95% CI, 1.4–1.7).
- Ages 35–44: PAS incidence 33.0 per 100,000 pregnant women versus NPAS incidence 31.0 per 100,000 nonpregnant women (IRR 1.1; 95% CI, 0.9–1.2).
- Ages 45–55: PAS incidence 46.9 per 100,000 pregnant women versus NPAS incidence 73.7 per 100,000 nonpregnant women (IRR 0.6; 95% CI, 0.3–1.4).
Proportionally, PAS accounted for a substantial share of strokes in younger women: 15–20 percent of strokes in women under 35 were pregnancy-associated (15 percent in ages 12–24 and 20 percent in ages 25–34). By contrast, PAS represented only 5 percent of strokes in women aged 35–44 and a very small fraction (0.05 percent) in women aged 45–55.
Comparing clinical characteristics, women with PAS had fewer traditional vascular risk factors than women with NPAS. Specifically, pregnant/postpartum stroke patients were less likely to have chronic hypertension, diabetes, or active smoking documented at hospitalization. Mortality was also lower among women with PAS compared with NPAS. These differences suggest distinct underlying mechanisms for stroke in pregnancy and postpartum women, especially in younger age groups.
Study authors caution that the research has limitations. The analysis relied on billing data (International Classification of Diseases, Ninth Revision codes), which can lack clinical detail and specificity for categorizing pregnancy-associated stroke subtypes. As a result, the findings are best interpreted as hypothesis-generating and warrant further research using more detailed clinical data and prospective designs to clarify causes and prevention strategies.
Clinical and public health implications: The results indicate that pregnancy and the early postpartum period are associated with an elevated stroke risk among younger women. Clinicians should be aware of this age-dependent pattern when counseling women of childbearing age and when evaluating neurologic symptoms during pregnancy and shortly after delivery. For older pregnant women, who are known to face increased risk for many pregnancy complications, this study suggests that pregnancy itself may not raise stroke risk beyond the baseline risk associated with age.
In conclusion, the New York State inpatient data from 2003–2012 show a higher relative incidence of pregnancy-associated stroke among women under 35 compared with their nonpregnant peers, while no increased relative risk was observed for older pregnant women. Additional research is needed to identify specific mechanisms, refine risk stratification, and develop targeted prevention and counseling strategies for pregnant and postpartum women.
Study details (Abstract summary)
Title: Risk of Pregnancy-Associated Stroke Across Age Groups in New York State. Design: Retrospective analysis of inpatient billing records from 2003–2012 identifying cerebrovascular events (transient ischemic attack, ischemic and hemorrhagic stroke, cerebral venous thrombosis, and nonspecified PAS) in women aged 12–55. Exposure: Pregnancy including the postpartum period up to six weeks after delivery. Main outcome: Incidence risk ratios for stroke by age cohort comparing pregnant/postpartum women with nonpregnant women. Results: 19,146 hospitalized stroke cases, 797 pregnancy-associated; younger pregnant/postpartum women showed significantly increased stroke risk compared with nonpregnant peers, while older pregnant women did not. Limitations: Billing data lack clinical granularity; findings are hypothesis-generating.
Research citation (as published): Eliza C. Miller, MD; Hajere J. Gatollari, MPH; Gloria Too, MD; Amelia K. Boehme, PhD, MSPH; Lisa Leffert, MD; Mitchell S. V. Elkind, MD, MS; Joshua Z. Willey, MD, MS. Risk of Pregnancy-Associated Stroke Across Age Groups in New York State. JAMA Neurology. Published online October 24, 2016. DOI: 10.1001/jamaneurol.2016.3774