Short-term growth in healthy infants, schoolchildren and adolescent girls

Background: There is agreement amongst most investigators now on the fact that growth, when measured over short periods, is an irregular and non- linear process. However, many aspects related to this process still remain controversial, for example, the continuity or discontinuity of the daily changes and the degree of existence of age differences in growth patterns. Aim: In this study we analyse and compare growth in height based on daily measurements in three samples of healthy children: Eight infants ( 1), 16 schoolchildren ( S) and 10 adolescent girls during their pubertal growth spurt ( A). Subjects and methods: Standing height or supine length were measured five times a week during 128 days, with Harpenden instruments and standardized techniques. A jump- preserving smoothing technique, based on the technical error of measurement ( TEM) with a hard rejection criterion was used to analyse our data. TEM varied between 0.08 and 0.20 cm. Results: Three types of events were found: ( 1) stasis ( changes in smoothed values indistinguishable from zero over 7 or more consecutive days), ( 2) steep changes ( any daily increment greater than 0.3 cm over 1 day), and ( 3) continuous growth ( small, and continued increments over time). The three types were present in all infants, adolescents and schoolchildren, with the exception of four schoolchildren who did not show steep changes. In the three samples, steep changes accounted for 32.7% ( r = 15.3 - 54.5%) of the total growth during the study period. Mean numbers of 1- day steep changes were 4.4, 1.4 and 2.1 for samples I, S and A, respectively. Mean numbers of stasis periods were 3.0, 2.9 and 4.3 for samples I, S and A, respectively. The longest stasis period observed was 28 consecutive days in one infant and one school child. Mean number of steep changes per child was significantly greater in infants. Conclusion: Our findings support the concept of growth as a non- linear and irregular process with three phenomena: Stasis, steep changes and continuous growth present in all ages, including infancy, school age and adolescence.