Early childhood growth trajectory and later cognitive ability: evidence from a large prospective birth cohort of healthy term-born children

Abstract

Background: Most studies of associations between child growth and cognitive ability were based on size at one or two ages and a single measure of cognition. We aimed to characterize different aspects of early growth and their associations with cognitive outcomes in childhood through adolescence.

Methods: In a sample of 12 368 Belarusian children born at term, we examined associations of length/height and weight trajectories over the first 6.5 years of life with cognitive ability at 6.5 and 16 years and its change over time. We estimated growth trajectories using two random-effects models-the SuperImposition by Translation and Rotation to model overall patterns of growth and the Jenss-Bayley to distinguish growth in infancy from post infancy. Cognitive ability was measured using the Wechsler Abbreviated Scales of Intelligence at 6.5 years and the computerized NeuroTrax test at 16 years.

Results: Higher length/height between birth and 6.5 years was associated with higher cognitive scores at 6.5 and 16 years {2.7 points [95% confidence interval (CI): 2.1, 3.2] and 2.5 points [95% CI: 1.9, 3.0], respectively, per standard deviation [SD] increase}. A 1-SD delay in the childhood height-growth spurt was negatively associated with cognitive scores [-2.4 (95% CI: -3.0, -1.8) at age 6.5; -2.2 (95% CI: -2.7, -1.6) at 16 years]. Birth size and post-infancy growth velocity were positively associated with cognitive scores at both ages. Height trajectories were not associated with the change in cognitive score. Similar results were observed for weight trajectories.

Conclusions: Among term infants, the overall size, timing of the childhood growth spurt, size at birth and post-infancy growth velocity were all associated with cognitive ability at early-school age and adolescence.

Keywords: Growth trajectory; IQ; Jenss-Bayley model; SITAR model; cognition; height.

Figure 1

Mean differences (95% CI) in cognitive score according to SD increases in individual growth parameters from the SuperImposition by Translation and Rotation (SITAR) and the Jenss-Bayley (JB) models for height. From the SITAR model, parameters α, β and γ represent the size, tempo and velocity, respectively. From the JB model, parameters a, b, c and d represent the size at birth, the growth rate after infancy, the degree of catch-up growth during infancy and the deceleration in the growth rate in infancy, respectively. The crude model only adjusted for clustering. The confounder-adjusted model included the growth parameters individually, adjusted for confounders. The fully adjusted model for the SITAR parameters included all three growth parameters, as well as confounders. The fully adjusted model for the JB parameters was built considering the temporal sequence of the estimated growth parameters: only confounders were included for parameter birth size (a) as the outcome; confounders and birth size for growth parameters of infancy (c and d); and confounders and birth size and growth rate in infancy for post-infancy growth (b).

Figure 2

Mean differences (95% CI) in change score according to SD increases in individual growth parameters from the Super Imposition by Translation and Rotation (SITAR) and the Jenss-Bayley (JB) models for height. From the SITAR model, parameters α, β and γ represent the size, tempo and velocity, respectively. From the JB model, parameters a, b, c and d represent the size at birth, the growth rate after infancy, the degree of catch-up growth during infancy and the deceleration in the growth rate in infancy, respectively. The crude model only adjusted for clustering. The confounder-adjusted model included the growth parameters individually, adjusted for confounders. The fully adjusted model for the SITAR parameters included all three growth parameters, as well as confounders. The fully adjusted model for the JB parameters was built considering the temporal sequence of the estimated growth parameters: only confounders were included for parameter birth size (a) as the outcome; confounders and birth size for growth parameters of infancy (c and d); and confounders and birth size and growth rate in infancy for post-infancy growth (b). The change score was calculated as the difference between the IQ scores at the ages of 16 and 6.5 years.