|Click on each chart to enlarge and print.|
The first step is to plot the child's height and age on the appropriate growth chart to determine what percentile group he or she is in. For example, say Boy A is 10 years old and 55 inches tall. This boy is right in the middle of the growth curve and will probably be average height as an adult, barring any physiological problems. Boy B is also 10 years old but stands only 50 inches tall. He would be in the 3rd percentile for boys his age and his final height may be quite short.
If height history is available, the physician can determine if the child has steadily followed one of the percentiles, or has suddenly dropped from one to another. For example, say Girl A's history is as follows:
Between ages 4 and 7 she was consistently around the 75th percentile. While she continued to grow, by age 9 she has dropped to the 25th percentile. This could indicate the onset of a growth failure. If, on the other hand, she had consistently placed near the 25th percentile, then she is probably short due to genetic factors. Unless her parents are in a significantly higher percentile, her growth is progressing well and is less of a concern.
The next step is to predict the child's final adult height. Predicting adult height is really an educated guess. Actual adult height depends on many factors including the child's health, nutrition, stress level and most importantly, genetics. The physician should ask about all of these factors as well as the heights of the child's parents and other relatives. If both parents are in the 3rd percentile for height, then it should not be surprising that Boy B described above is also in the 3rd percentile for boys age 10. If Boy B consistently placed in the 3rd percentile during his 10 years, then in all likelihood, he will continue to grow according to his placement on the curve and should be expected to reach a height near his parents. However, if his parents are in a significantly different percentile, there may be a problem, and a physical exam is indicated. Of course the boy's father and mother may be in two different percentiles, which makes the prediction of Boy B's adult height more complicated.
It is quite common for boys and girls to grow suddenly as they enter puberty. This is called the growth spurt. If you look closely at the boys and girls charts above, you can see that the curves are relatively flat from age 4, then increase slightly just before the child enters puberty. The graph below shows this more clearly:
Here the vertical axis is growth per year. From ages 4 through 12, boys grow at a relatively constant rate of 2½ inches per year, slowing down as they reach age 12. Between 12 and 15, their growth rate increases significantly, peaking at 4 inches per year, then stopping at around age 18. Girls start to peak earlier, from ages 10 to 13, then slow down until growth ends at around age 15.