Latent motor growth trajectories of term and preterm infants based on caregiver report.

Early motor development is a key predictor of development in other skill domains and specific neurodevelopmental disorders, but it is typically measured as achievement of milestones rather than rate of development. To explore the value of the latter approach, this study utilized a novel caregiver report method to examine differences in the developmental trajectory of motor development in term-born compared to preterm-born infants. Caregiver-infant dyads (331 term, 240 preterm) were followed from birth through 12 months (48% female; 6.4% Hispanic; 34.1% Black; 10.3% Mixed or Biracial; and 48.3% White). Longitudinal Item Response Theory (IRT) modeling was used to compare growth trajectories of motor skills between term and preterm infants. The moderating effects of biological sex on group differences also were examined. The main effect for term status was significant. Preterm infants exhibited slower rates of growth in motor ability over the first 12 months compared with term infants. Differences in rate of growth were significant by 6 months of age. In the term group only, females exhibited more rapid growth than males in motor ability. Findings indicate that caregiver report yields reliable estimates of growth in the latent trait of motor ability, with slower rate of growth in infants born preterm. Estimates of latent growth in motor ability may provide more sensitive measures of neurodevelopmental risk and a method to examine response to treatment.