Chart for boys|
Chart for girls
Take the example of percentile charts of height for age, 2-18 years. If a 6.5 year old girl's height is 110 cm, then her height is on the 10th centile. That means, if 100 girls of her age are arranged in ascending height then she is at the 10th position - taller than 9 girls, but shorter than 90 girls. Her height is within normal limits. Probably one of her parents has a height at the 10th centile too.
Since most people would stop growing (in height) after 18 years, adult height can be plotted at 18 years of the same sex. It is very likely that either her mother measures 151 cm or her father measures 162 cm both at the 10th centile. In assessing the growth pattern of an infant less than 2 years it is also encouraged to refer to the 2-18 years chart. If the parental size, particularly height, was plotted at 18 years of the same sex, one would have a better idea what the genetic growth potential of that infant should be.
Shortness is a relative term. An individual whose height is on the 3rd centile is shorter than another whose height is on the 50th centile, who in turn is shorter than another whose height is on the 97th centile. Clinically, one is considered to be short if he/she is below the third centile or short compared to his/her parents' height percentiles. Height is normally distributed. Therefore, it is expected that 3% of the normal population would be below the third centile and they can be normal. However, if they are too much below the third centile, it is more likely that they had pathological reasons.
What is more useful is to see the trend. If there is a downward drifting in the percentile position, there is a greater chance that they suffer from an illness. For example, if the height of a girl drifted from the 25th centile at age 4 to the 3rd centile at age 6 or even further to 2 cm below the 3rd centile at age 8, then this girl might be suffering from a disorder. There are exceptions where crossing downward centile can be physiological. Firstly, for a child who has physiological delay in puberty or constitutional delay in maturation, there could be a period of slower growth compared to the others before he/she goes into the growth spurt. Secondly, during the first year of life, physiological shifting can occur when the factor determining growth is switching from maternal size and maternal nutritional status during intrauterine life to his/her own inherited genetic growth potential.