The Importance of Assessing Growth in Infants and Young Children

Monitoring growth is central to the practice of paediatrics, improving public health, and health screening of young children. The measurement of growth is universally used by health-care professionals to assess an individual child’s physical, emotional, and social development but is also a strong indicator of population health and hence a key tool for public health surveillance. This dual and overlapping role for the assessment of growth inevitably leads to differences between individuals and populations in definitions of normal and abnormal growth patterns and their impacts on health.

At an individual level, growth can be assessed as changes in anthropometric measures of body size arising from interacting genetic and environmental factors such as nutrition and socio-economic status. The pattern of growth (rather than attained size) is compared to standards such as the WHO growth standards which are based on selected, healthy, and well-nourished populations, and describe how children should grow. These standards have made a major contribution to the harmonisation of growth assessment globally, although they are not applicable to all countries and populations.

For individual children assessing whether their pattern of growth is comparable to the WHO growth standards is an essential part of their clinical care. Inadequate growth or “growth faltering” refers to children with a slower rate of weight than expected for their age and gender and has varying definitions such as a fall in weight for age of >1 standard deviation (z-score) over 1 month [1, 2]. Although commonly caused by multiple factors, faltering growth is traditionally classified as illness or not-illness related and is particularly common in hospitalised children with rates as high as 51% in some studies [2]. Faltering growth is associated with increased morbidity, mortality, length of hospital stay, and rates of readmission in the short-term, and reduced school performance and cognitive development in the longer term. Consequently, the diagnosis and management of faltering growth, including appropriate nutritional assessment and promotion of catch-up growth, is a major focus of health-care systems globally [1].

At a population level, attained size (rather than the pattern of growth) is widely used to define normal or abnormal growth and as an indicator of population health. Cut-offs of <2 z-scores for length/height, and weight for length/height, are used to define stunting and wasting respectively. As with individuals, poor growth in populations has important health impacts. Population rates of stunting and wasting defined using the above cut-offs correlate with population rates of childhood mortality, while growth trajectories from conception to 2 years of age predict intelligence quotients in adults and strongly influence a population’s productivity and human capital. Interventions to support optimal growth, particularly those focussing on the diagnosis, prevention, and treatment of nutritional deficiencies are therefore critical for population health.

Previously, the assessment of growth has focused predominantly on the diagnosis, and treatment of malnutrition, faltering growth and stunting. While these continue to be a global health burden, growth is now recognised to strongly influence or “programme” the risk of later obesity. Upward centile-crossing for weight, or “growth acceleration,” in infancy increases the risk of later obesity and cardiovascular disease [3] and differs from catch-up growth following growth faltering [4]. Greater weight gain in infants formula-fed rather than breastfed could also explain higher later rates of obesity associated with formula feeding possibly because of the higher protein content of infant formula compared to breast milk.

Although there is little doubt that the assessment of growth is critical for optimising health in both individuals and populations, despite decades of research, several scientific and practical questions remain unanswered. For instance, comparing an individual’s growth pattern to a standard describes how a child is growing but not the pattern of growth that is desirable in terms of health outcomes. Also unknown are the critical windows and mechanisms for programming effects of growth, and the optimal risk balance of promoting faster infant growth for different health outcomes and in populations at different stages of development [4]. Other key issues facing health-care professionals are how best to assess growth in preterm infants and communicate problems with growth to parents and carers. The four expert reviews in this issue address some of these key questions and summarise the evidence as to why assessment of early growth is so critical for the health of children throughout life.