Describing the Shape of the Relationship Between Gestational Age at Birth and Cognitive Development in a Nationally Representative U.S. Birth Cohort.

BACKGROUND Preterm children face higher risk of cognitive and academic deficits compared with their full-term peers. The objective of this study was to describe early childhood cognitive ability and kindergarten academic achievement across gestational age at birth in a population-based longitudinal cohort. METHODS The study population included singletons born at 24-42 weeks gestation enrolled in the Early Childhood Longitudinal Study-Birth Cohort (n = 6150 for 2-year outcome, n = 4450 for kindergarten outcome). Home-based assessments measured cognitive ability at 2 years and reading and mathematics achievement at kindergarten age. Linear regression models estimated the association between gestational age and cognitive and academic scores using four different ways of modelling gestational age: continuous variable in linear and quadratic terms; categories for individual weeks; and clinical categories for early preterm, moderate preterm, late preterm, early term, full term, late term, and post-term. RESULTS Children born at early preterm (24-27 weeks), moderate preterm (28-33 weeks), and late preterm (34-36 weeks) scored significantly worse than full-term (39-40 weeks) peers on 2-year and kindergarten assessments; however, no deficits were observed for early term (37-38 weeks). These categories were a clinically useful and parsimonious approach to stratifying risk of adverse cognitive and academic outcomes. CONCLUSIONS This study estimated the relative performance of children born at 24-42 weeks in a population-based birth cohort using multiple approaches to modelling gestational age, providing a more rigorous understanding of the relationships between the full spectrum of gestational age and cognitive and academic outcomes in early childhood and at school age.