Supplementary Material for: Incidence Estimates of Perinatal Arterial Ischemic Stroke in Preterm- and Term-Born Infants: A National Capture-Recapture Calculation Corrected Surveillance Study

<b><i>Introduction:</i></b> Data on valid incidence estimates of perinatal arterial ischemic stroke (PAIS) are scarce. This analysis aims to determine incidence of PAIS in term- and preterm-born infants and to investigate clinical differences related to prematurity. <b><i>Methods:</i></b> This surveillance study (2015–2017) in all German paediatric hospital estimated incidences for MRI-confirmed PAIS in term and preterm infants. To correct for under-reporting, we performed capture-recapture-calculations (CRC) in the most populous federal state and extrapolated nationwide. Differences in clinical presentation in term- and preterm-born infants were assessed. <b><i>Results:</i></b> 126 term- and 19 preterm-born infants with PAIS were reported. CRC corrected incidence of PAIS was 22 (95% confidence interval [CI] 17, 27) per 100,000 live births. Stratified by prematurity, the incidence was 32 (95% CI 15, 49) per 100,000 in preterm-born infants and 21 (95% CI 16, 26) per 100,000 term-born infants (significant difference <i>p</i> = 0.001). In symptomatic cases only (<i>n</i> = 120 term born, <i>n</i> = 12 preterm born), incidences did not differ. Risk factor patterns were similar, but number of risk factors in preterm babies was elevated (mean 3.8 vs. 2.9; <i>p</i> = 0.01) and median age at diagnosis was increased (5 vs. 3 days; <i>p</i> = 0.04). Clinical seizures were observed in 88% (106/120) of symptomatic term infants compared to 33% (4/12) in preterm-born infants (<i>p</i> &lt; 0.0001). <b><i>Conclusion:</i></b> PAIS incidence rates in Germany, extrapolated from estimates for completeness of reporting in the largest federal state, were within the range of other population-based studies. As a novel finding, we detected symptomatic PAIS in preterm-born infants to be as common as in term-born infants although their symptoms were often unspecific.