Understanding Growth Charts
Nixie Raymond, M.S., R.D., Newton-Wellesley Hospital
When evaluating a child’s growth, an essential tool is the growth chart. Growth charts are reference standards that depict normal growth for male and female children from infancy to 18 years of age. The standards were developed from studies in which large numbers of healthy children were measured and weighed at various ages. The data was used to develop growth curves which illustrate not only a child’s expected weight and height at a single age, but also predict the pattern of growth over time. The growth chart consists of a grid with age plotted along the horizontal line, and weight and height along the vertical line. Each curve on the growth chart represents a percentile (from 5th to 95th) indicating the position a measurement would hold in a group of 100. For example, in Figure 1 the 8-year old boy weighing 25 kg (55 pounds) is at the 50th percentile, indicating that in a group of healthy reference children, 50% would weigh more, 50% would weigh less. At age 9 1/2, the child weighs 26.5 kg (58 pounds) and is at the 25th percentile; so 75% of boys his age weigh more than he, 25% weigh less. The range of weights generally considered normal is from the 10th to 90th percentiles. Values outside of this range may represent weight deficit or excess.
In addition to plotting a child’s current weight and height on a growth chart, it is also very important to consider previous measurements to determine if the child’s growth fits the expected pattern. Although growth does not always proceed along as smooth a curve as the charts suggest, it is expected that most children will stay approximately along the same weight and same height percentiles during growth. This is illustrated in Figure 2 in which a girl’s height tracks along the 10th percentile and weight along the 25th percentile. Note that while this girl’s current height at the 10th percentile may initially suggest poor growth, her history indicates that she has had normal growth along this curve for many years and her current height is probably appropriate for her. ‘In contrast, the boy’s weight in Figure 1 has fallen from the 50th percentile to the 25th percentile, suggesting poor weight gain and indicating the need for and/or further assessment.
It is important to remember that although nutritional status may impact on growth, a child’s growth potential is determined by genetics. Correction factors using mid-parental heights have been developed and may be used to account for genetic influences when evaluating a child’s growth.