Growth chart curves do not describe individual growth biology

Abstract

Growth reference tables present statistical distributions of size for age of individuals within a sample or population. As summaries of phenotypic variability at the group level, they document that individuals grow by different rates during similar time frames. The data are commonly fitted by mathematical functions to produce the convex curves of percentile distributions useful for infant and childhood growth monitoring. In this form, the growth chart appears to be a frame of reference for judging how well an individual infant/child is progressing through time by comparison with peers across ages. This has led to the assumption that individuals should track in these channels during growth. The interpolated lines between the statistical distributions of size for age at the level of the population do not, however, represent how individuals grow. Growing is an individual process characterized by nonlinear episodic saltatory increments that result in shifting size relationships among similarly aged peers over short time intervals. Data from a prospective, longitudinal study of infants illustrate the poor performance of growth chart curves as representations of individual growth. Clarification of the paradigms supporting perceptions of normal growth patterns is useful both practically and theoretically: growth chart patterns have important clinical sequelae when this informs feeding recommendations. Further characterization of individual growth patterns will contribute to increased understanding of both individual growth biology and the nature of adaptability.

Child Growth: Concept Analysis

“…2 It is an individual process characterized by a nonlinear episode that results in change of size between similar ages within a short time span. 15 It is the major biological event in childhood. Morphologically, it reflects the integration of multiple signals in a dynamic process, and flexibility and diversity of results are documented by variability in the phenotypic size characteristics of the human population as a whole.…”

“…Growth comprises spaces in the individual: cells; tissues; and process at the organic level mediated by the interrelation between genome and local physiology to set specific ways through which the organism increases in the size and age of the immature system. 15 Growth is cell division and the consequent increase of body mass that can be identified in units such as g/day, g/month, kg/year, cm/year-that is, increase in the mass unit in a given time unit. 12 Physical development is top-to-bottom (cephalocaudal pattern) and from the center of the body to outside (proximodistal pattern).…”

Growth and Life Course Health Development

“…While a common diagnostic approach in the clinical setting, this is problematic. Growth charts are merely summary statistics of size for age and are not designed to represent growth paths followed by individuals (Lampl and Thompson 2007); any "pattern" only reflects how an individual's size compares to peers of similar age, who themselves are not staying the same relative to one another. The WHO child growth standards, widely implemented in clinical practice for identifying pathological growth , were developed from data collected by international sampling among "healthy" breastfed infants, with the goal of representing optimal growth trajectories (WHO MGRS 2006).…”

“…Children are compared with peers of similar age and background for perspective on how they are faring relative to one another on "growth charts" produced, for example, by the US Centers for Disease Control and Prevention (CDC) (Kuczmarski et al 2000) and assessed for how they should be growing under optimal circumstances, as proposed by the World Health Organization (WHO) (WHO MGRS 2006). It is important to note that these assessments actually compare size, an indication of how much growth has occurred previously, but do not provide information on growth itself as represented by the pathway taken to achieve current size (Lampl and Thompson 2007) and are often mistakenly assumed to provide details of growth biology (Lampl 2012a). Growth is an emergent process at the individual level; trajectories of growth in height, weight, and body composition offer a phenotypic reflection of the complex interactions between macro-and microlevel processes that influence life course health development.…”

Historical Approaches to Human Growth Studies Limit the Present Understanding of Growth Biology

“…These charts are commonly referred to as ‘growth charts' or ‘growth curves'. While useful visual tools for the purpose of comparative size-for-age estimates, caregiver [9] and healthcare worker [10] comprehension of the information presented can be limited and these charts are not necessarily representative of the growth trajectories followed by individuals [11]. Instead, the curves are interpolations, or mathematical inferences, of growth rates.…”