Bimodal Dynamics in Short-Term Growth Among Peruvian Infants at Risk of Growth-Faltering

Abstract

Objectives Over the short term, infants may grow in a ‘bimodal’ manner, with interspersed periods of greater and lesser growth. Our aim was to describe the modality of high-resolution growth dynamics of infants who experienced cumulative growth faltering in the first year of life. Methods Thrice-weekly measurements of length were recorded for n = 58 children enrolled from birth to one year in the Peru cohort of the Etiology, Risk Factors and Interactions of Enteric Infections and Malnutrition and the Consequences for Child Health and Development’ (MAL-ED) study. Finite mixture models were fitted to the length velocity data to test for evidence of multiphasic patterns. We then tested whether evidence of a multiphasic pattern remained after applying a smoothing algorithm to account for measurement error. Data was smoothed using kernel regression with a monotonic constraint. Finite mixture models were fitted to unsmoothed and smoothed data to examine whether growth patterns varied by age and sex. We also fitted stratified models to compare short-term growth patterns between infants who maintained a consistent length-for-age Z-score (LAZ) from 2–12 months of age, versus those whose LAZ decreased by at least 0.25 over the same period. Results Unsmoothed data were best described by a biphasic finite mixture model. The growth of children less than 3 months old was described by a mixture of two normal distributions with both means significantly greater than zero (0.110 cm/day, 95%CI: 0.105, 0.114 and 0.291 cm/day, 95%CI: 0.235, 0.347). By 6 months, this transitioned to a pattern of two normal distributions, one with a mean near zero (0.019, 95% CI: 0.0178, 0.020), and one with a mean of 0.102 cm/day (95% CI: 0.098, 0.0107). Children who lost 0.25 or more in LAZ from 2 to 12 months had a similar mean growth velocity in both the ‘low’ and ‘high’ growth phase but spent smore time in the former phase (54.9% of days versus 39.2% of days) than children who either maintained or gained LAZ over the same age. Conclusions Consistent with other reports, we find that infant growth appears to follow bimodal dynamics characterized by intervals of greater velocities as well as periods of much lower growth. Funding Sources This work was supported by the National Institutes of Health and the BMGF.