The National Center for Health Statistics has developed growth charts that are used to compare a child's measurements with those of other children the same age. By plotting a child's measurements on these charts, doctors are able to compare individual growth patterns with data collected on thousands of U.S. children. This helps to determine whether a child's growth is normal compared with others the same age. Boys and girls are plotted on different charts because of their difference in growth rates and patterns. There are two sets of standard charts for both boys and girls: one for infants ages newborn to thirty-six months, and another for children ages two to twenty years. The charts are a series of percentile curves that show the distribution of growth measurements of children from across the country.
ALERT! Only those measurements obtained in your child's doctor's office or taken by another health professional should be plotted. Many times home measurements are inaccurate and inconsistent, which can lead to incorrect data and unnecessary concern.
During your child's routine visits to the doctor, certain measurements will be taken and recorded in the child's medical record. With an older child, a doctor may plot up to four numbers on the growth chart: height for age, weight for age, weight for height, and (a recent addition) body mass index (BMI). Infants are usually measured for length for age, weight for age, weight for length, and head circumference for age.
A growth chart contains seven curves, which all follow the same standard pattern. Each curve represents a different percentile: the fifth, tenth, twenty-fifth, fiftieth, seventy-fifth, ninetieth, and ninety-fifth. The fiftieth percentile represents the average value for age. A child's continued growth measurements are plotted among the percentile curves. For example, an infant whose head circumference falls in the ninetieth percentile is plotted on the second curve from the top of the chart. Being in the ninetieth percentile means the child's head measurement is greater than or equal to the measurements of 90 percent of children in the country in the same age category. The remaining 10 percent of children that age have greater head measurements. Just because a child has a high or low reading does not always mean there is a problem.
Generally if a measurement exceeds the ninety-fifth percentile, or if it crosses two percentile curves (for example, climbing from the forty-fifth to the seventy-fifth percentile, thereby crossing the fiftieth and seventy-fifth percentile curves), there may be some cause for concern.
If a measurement falls below the fifth percentile, or if it crosses two percentile curves (for example, dropping from the fiftieth to the twentieth percentile), there may be some cause for concern. The doctor may consider health problems affecting the child's normal growth pattern.
Growth charts can be valuable tools, but it is important not to focus too much on any one reading. When growth chart readings are examined over time, they reveal a pattern of development. It is the pattern that tells you whether a child is growing properly in relation to other children of the same age. The pattern also shows how the child is progressing from measurement to measurement. This is a much more useful indicator of a child's development than any single measurement.If you're curious about how tall your child may grow to be, try our new Child Height Predictor.