Longitudinal BMI Growth Curves for Surviving Preterm NICU Infants Based on a Large US Sample.

Background: Longitudinal growth curves, based on repeated measurements from the same group of infants, exist for preterm infant weight and length but not for BMI. Our existing BMI (weight divided by length squared) curves are based on cross-sectional birth data obtained from a different group of infants at each gestational age (GA).

Methods: We calculated BMI over time for 68 693 preterm infants between 24 and 36 weeks GA.