Objective:To investigate whether previously reported increasing incidence of pregnancy-associated stroke (PAS) is observed in chart-validated register data in Finland. In an exploratory analysis, we studied risk factors for PAS.Methods:We performed a retrospective population-based cohort study and nested case-control study in Finland 1987-2016. The Medical Birth Register (MBR) was linked with the Hospital Discharge Register to identify women with incident stroke (ischemic stroke, cerebral venous thrombosis, intracerebral or subarachnoid hemorrhage) during pregnancy or puerperium. Cases were verified from patient records. Incidence of PAS over the study period, in 5-year age groups and pregnancy/postpartum period were calculated per number of deliveries. Three matched controls were selected for each case from MBR to compare risk factors.Results:After chart review, 29.6% (257/868) of cases were PAS. The incidence of PAS was 14.5 (95%CI: 12.8-16.3) per 100,000 deliveries. Incidence increased from 11.1 to 25.2 per 100,000 deliveries from 1987-1991 to 2012-2016 (p<0.0001). Incidence increased by age from 9.8 to 29.9 per 100,000 deliveries from ages 20-24 to ages >40 (p<0.0001). During early postpartum period, incidence was 5-fold greater compared to the first trimester. Maternal mortality was 6.6%. In the multivariable adjusted model, smoking beyond 12 gestational weeks (odds ratio [OR] 1.8, 95%CI: 1.2-2.7), migraine (OR 16.3, 95%CI: 5.3-49.8), and hypertensive disorders of pregnancy (OR 4.0, 95%CI: 2.5-6.3) were the most important risk factors for PAS.Conclusion:PAS incidence is increasing stressing the importance of careful pregnancy surveillance and risk factor management, particularly in older expectant mothers and extending to puerperium.Classification of Evidence:This study provides Class III evidence that smoking beyond 12 gestational weeks, migraine and hypertensive disorders of pregnancy are associated with an increased risk of PAS.