What is Known: • Existing neonatal hematologic reference intervals often lack stratification by gestational age and fetal growth. • This limits their utility in preterm and small-for-gestational-age infants, who have unique hematologic profiles due to distinct developmental trajectories and potential perinatal complications. What is New: • This study establishes hematologic reference intervals stratified by gestational age and postnatal age specifically for preterm neonates. • It further highlights key differences between appropriate-for-gestational age and small-for-gestational age infants, improving the diagnostic accuracy for this vulnerable population.