How big should your child be?

Apr 27 2004

Each time you take your child to an annual checkup, most likely the first thing the doctor or nurse does is record your child's current height and weight. The two numbers are then plotted on separate gender-specific graphs to indicate what percentile your child falls into. This result is sometimes a surprising measure of much your child has grown over the past year. But what do these percentiles really tell you?

Well, it's a good indication of whether your child is growing steadily or heading off the "curve." For example, a child who consistently has had a weight percentile of 50 percent, but is now at 75 percent, may be headed toward obesity.

While these percentile charts can give you an idea of how your child is growing, many doctors are now using another growth measure called a body mass indicator (BMI). The BMI calculator compares a child's weight and height for her age, coming up with one number, rather than separate ones. This calculation is particularly helpful for identifying children and adolescents who are at risk for becoming significantly overweight, because there's a strong correlation between BMI and body fat.

What's your child's BMI? You can find online calculators, but to do it by hand you can use this method: Take your child's height and multiply it by itself. Then divide his weight by the number you got from the height equation. Once you have that answer, multiply it by 703.

Your child's doctor can plot her BMI on a gender-specific percentile BMI-for-age chart. This measurement provides a snapshot of your child's weight and height for age, giving you an important visual cue for changes in your child's weight. For example, a girl with a BMI that puts her in the 50th percentile at age 5 would be expected to gain weight at a rate that keeps her BMI "tracking" along the 50th percentile as she grows.

The real value of BMI measurements lies in viewing them as a pattern over time. Any one-time calculation is not a reason to panic, but an opportunity to keep a closer eye on your child's diet and activities. After all, encouraging healthy eating and an active lifestyle is a good idea for kids (and adults) at any age and weight.

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