Body size is important at all ages, but particularly at birth because of its relationships to morbidity and mortality in early infancy and its possible relationships to some diseases in adulthood. Reference data for size at any age allow the recognition of infants with unusual values. Measuring the size of infants and children and comparing the values with appropriate reference data are important parts of a pediatric health assessment. Body measurements are primary indicators for monitoring growth, health, and nutritional status and they provide information regarding future health potential. Infants and children with normal body size are probably receiving adequate nutrition and growing appropriately and are less likely than others to have diseases.

The patterns of growth during infancy differ from those in childhood and adolescence. Consequently, separate sets of growth charts are needed for these periods of growth. Following rapid growth during the first two years after birth, growth proceeds at a relatively steady pace until pubescent accelerations bring children close to their adult body size. Body size is important after infancy in relation to current nutritional status and the probability of current and future diseases.

Differences between males and females in growth after infancy are well documented. One major difference is that males, on average, have pubescent growth spurts about one to two years later than females. Growth is more rapid in males than females during pubescence and pubescent growth lasts longer in males than females.