Objective To evaluate the relationship between prolonged neonatal intensive care unit (NICU) stay after birth and childhood neurodevelopmental measures from age 9 months to kindergarten.

Design Longitudinal birth cohort study.

Setting and patients This study examined a nationally representative sample of 10 700 participants from the Early Childhood Longitudinal Sample—Birth Cohort and selected those who had a NICU stay (n=2100). These children were followed from birth to kindergarten.

Predictors Days in the NICU.

Main outcome measures Childhood neurodevelopmental and early academic scores.

Results Increasing length of stay in the NICU had a significant negative relationship with the 9-month and 24-month Bayley mental and motor scores. Each additional week in the NICU increased the odds of scoring in the lowest 10% on the Bayley 9-month mental (OR 1.08, 95% CI 1.034 to 1.122) and motor (OR 1.11, CI 1.065 to 1.165) assessments and 24-month mental (OR 1.09, CI 1.041 to 1.144) and motor assessments (OR 1.07 CI 1.017 to 1.123). Gestational age was not significantly related with these measures in our model. Increasing socioeconomic status had a significant positive relationship with preschool and kindergarten reading and math scores and a lower odds of scoring in the lowest 10% in these measures.

Conclusion Increasing length of NICU stay was predictive of decreased child development measures in early childhood (9 and 24 months), while socioeconomic status was a better predictor at later assessments (preschool and kindergarten entries). Gestational category did not account for these differences. These data may have implications for counselling parents regarding potential neurodevelopmental consequences following NICU stay.