For years, physicians have charted children's height and weight to determine if they are growing normally. Physicians can also use a body mass index (BMI) as an additional tool, which may aid them in determining if the amount of body fat is appropriate. According to the Centers for Disease Control (CDC), while BMI does not measure body fat directly, it correlates to direct measurements of body fat such as underwater weighing or dual-energy X-ray absorption.
Determining Height and Weight
The first step in determining your child's BMI is to accurately determine her height and weight. The best way to measure your child is to remove her shoes, bulky clothing and hair ornaments, and unbraid hair that may be in the way. Then have your child stand feet together, looking straight ahead, next to a wall on an uncarpeted floor. Use a ruler positioned parallel to the floor to touch the top of the child's head and mark the height measurement on the wall. Then measure the height from the floor to the mark on the wall to the nearest 1/8th of an inch.
Weigh your child without shoes and heavy clothing. On an uncarpeted floor with a digital scale, have the child stand with both feet together in the middle of the scale. Record the weight to the nearest fraction.
Calculations
BMI is calculated by taking the child's weight in pounds and dividing it by the height in inches squared, then multiplying the result by 703. After BMI is calculated, it is compared against the CDC's age growth charts for both boys and girls to obtain a percentage. Since BMI for children and teens is sex and age specific, it is termed "BMI for age."
Interpretation
After the calculation is made and the percentage is found, the weight status category can be determined. Children and teens who are at the fifth percentile or less are in danger of being underweight. Children and teens who fall between the 5th to 85th percentiles are considered to be a healthy weight. Falling between the 85th and 95th percentiles is considered overweight. At the 95th percentile or higher, the child or teen is considered obese.
Recommendations
Both the CDC and the American Academy of Pediatrics recommend using BMI as a screening tool starting at age 2 and continuing until age 19. They stress that this is only a screening tool and not a diagnostic one. A child or teen with a BMI in the underweight, overweight or obese categories should be seen by a doctor, who can do further assessments. These assessments may include skin fold tests, nutrition counseling, and evaluation of physical activity and family history. Children and teens may have a high BMI if they have a large frame or a lot of muscle. Additionally, there is often a jump in the BMI during puberty.
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