You might assume that your child's heaviest friend isn't as healthy as his average-sized friend, or that his tiny friend isn't getting quite enough to eat, but size isn't always an indicator of health, according to the website, KidsHealth. Pediatricians rely on height and weight charts for kids to determine whether they are developing at a steady pace based on individual factors, such as heredity and individual growth trends.
Significance of Charts
Children aren't all measured by the same chart. For example, different charts measure boys and girls, because they don't grow in the same way, states KidsHealth. However, all charts measure the same features of your child and others. Doctors will measure and chart your child's head circumference, length and weight until she's 36 months; for older kids, doctors chart height, weight and body mass index.
What Percentiles Mean
Your pediatrician uses your child's various measurements to determine what percentile your child is in for each measurement. Percentiles essentially tell you how your child compares with other children of the same age and sex. If the chart says that 90 percent of all of your child's peers are taller than she is, she falls in the 10th percentile for height. If she is in the 50th percentile for weight, she is at the average weight for children of her age and sex.
The body mass index, or BMI, formula indirectly assesses whether your child is in a healthy weight range, according to the Centers for Disease Control and Prevention. After your pediatrician plugs your child's weight and height into the BMI formula, he plots the resulting number onto a BMI chart for children of the same age and sex. Your child is considered underweight if he is under the fifth percentile, in a healthy range if he is at the fifth but under the 85th percentile, overweight if he is at the 85th percentile but under the 95th and obese if his BMI is at or over the 95th percentile, reports the CDC.
Reasons for Concern
Your child's percentile for any given measurement is less significant than her overall growth rate. The pediatrician may express concern about your child's size if your child's percentiles change dramatically, according to KidsHealth. If she was once in the 80th percentile for height and weight and then her height drops to the 40th or 50th percentile at her next visit, there could be cause for concern or it might be that she's just be going through a temporary growth lull. The pediatrician may express concern if your child's weight percentile is dramatically higher than her height percentile. Additionally, if your child's weight falls under the third percentile or if it is 20 percent under the ideal weight for her height, she might be diagnosed as failing to thrive, according to MedlinePlus.
Charts and numbers don't tell the whole story of your child's health. Your pediatrician will also consider factors such as your child's genes, health, diet and exercise to interpret the chart results, according to KidsHealth. If, for instance, your child's BMI percentile is high, he may actually be muscular. Your pediatrician may then rule out health problems by performing assessments such as a skinfold thickness test. Alternately, if your child's height and weight are suddenly on the low end, your pediatrician may test your child's blood and urine to rule out any potential health problems.