A growth chart is used by pediatricians and other health care providers to follow a child's growth with age. Growth charts have been constructed by observing the growth of large numbers of healthy children over time. The height, The body weight, and head circumference of a child can be compared to the expected parameters of children of the same age and sex to determine whether the child is growing appropriately. For each parameter, a set of growth curves are graphed for the median value (the "middle" value, at 50 percentile), lower and upper quartiles (bottom and top 25%), as well the lower and upper deciles (bottom and top 10%). Growth charts can also be used to predict the expected adult height and weight of a child because, in general, children maintain a fairly constant growth curve. When a child deviates from his or her previously established growth curve, investigation into the cause is generally warranted. Parameters used to analyze growth charts include weight velocity (defined as rate of change in weight over time), height velocity (defined as rate of change in stature over time), and whether someone's growth chart crosses percentiles. For example, endocrine disorders can be associated with a decrease in height velocity and preserved weight velocity while normal growth variants are associated with a decrease in height and weight velocity that are proportional to each other. Other parameters are more commonly used such as waist circumference for assessing obesity and skin fold difference for assessing malnutrition. Growth charts can also be compiled with a portion of the population deemed to have been raised in more or less ideal environments, such as nutrition that conforms to pediatric guidelines, and no maternal smoking. Charts from these sources end up with slightly taller but thinner averages.
Growth charts are different for boys and girls, due in part to pubertal differences and disparity in final adult height. In addition, children born prematurely and children with chromosomal abnormalities such as Down syndrome and Turner syndrome follow distinct growth curves which deviate significantly from children without these conditions. As such, growth charts have been created to describe the expected growth patterns of several developmental conditions. Since there are differences in normal growth rates between breastfed and formula-fed babies, the World Health Organization growth charts, which better reflect the growth pattern of the healthy, breastfed infant, are considered the standard for U.S. children under age two.
History and revisions to growth charts The history of growth charts dates back to the 19th century. Regarding growth velocity, in 1829, Louis-René Villermé found that slower growth velocity could be attributed, in part, to poverty. In 1870, Adolphe Quetelet noted that there were periods of more or less rapid growth, in particular around the age of puberty and following illnesses. Other historical contributors to the study of child growth include Edwin Chadwick, Charles Roberts (d. 1901), Henry Pickering Bowditch and Franz Boas. In 1977, the National Center for Health Statistics (NCHS) developed a growth chart to clinically analyze child development. This growth chart was subsequently used by the World Health Organization for dissemination to healthcare systems abroad. However, there were limitations to this growth chart. First, the sample population was restricted to children of European ancestry from a single community in the United States. Second, while it did use a longitudinal study design, the focal children were only measured every three months, which did not sufficiently describe the rapid and changing rate of growth in early infancy. Third, the statistical methods available at the time resulted in inappropriate modelling of the pattern and variability of child growth, especially in early infancy. Acting on this, in the 1990s the World Health Organization set out to create more representative growth references. In the WHO Multicentre Growth Reference Study, between July 1997 and December 2003, longitudinal and cross-sectional growth data were collected from 8440 breastfed children, from six countries (USA, Oman, Norway, Brazil, Ghana, India) in socio-economic conditions favourable to growth. These data included anthropometrics, as well as motor development, feeding practices, child morbidity, perinatal factors, and socio-economic, demographic and environmental characteristics. It is against these growth references that the United Nations Sustainable Development Goals are measured. The use of one growth reference for all children is appropriate. Children included in the WHO Multicentre Growth Reference Study were ethnically and geographically diverse. Height is a highly heritable trait; about 80% of the variation in height is attributable to variation in genes. At the same time, it has long been known that genetic variation within racial groups exceeds variation between groups (see The Apportionment of Human Diversity). Unsurprisingly, in the WHO Multicentre Growth Study, only three percent of the variation in height was attributed to variation between sites, while 70% of the variation was attributed to variation within sites. In addition to international growth references, some countries choose to use their own growth references. For example, in the United States, data used to calculate the CDC's growth chart percentiles was accumulated periodically since the 1960s by the National Health and Nutrition Examination Survey. Updated and more comprehensive data was later used to revise the existing growth chart and construct the 2000 CDC growth charts. The revised growth charts include revision of the 14 existing charts as well as introduction of 2 new BMI-for-age charts.
Quantitative definitions Mid-parental height (MPH) is often used to predict the target height of an individual based on the heights of the two biological parents. It can be used to calculate the target height (TH) for children. MPH is given as simply the mathematical average of the heights of the child's parents:
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