How Does the Growth Chart Determine the Weight Category for My Child?
For children older than 2 years old the body mass index (BMI) is calculated using your child's height to weight ratio. It is the best standard available for defining measurements that classify as underweight, overweight or obese. This is the exact calculation:
BMI = body weight (kg) ÷ height (meters) squared
BMI varies with age, gender, and pubertal stage, so growth standards are based on BMI percentiles. The calculated BMI is plotted on a BMI reference chart to determine the BMI percentile. There are different growth charts for males and females. All children older than two years should have their BMI calculated at least annually; this allows for your pediatrician to watch the trend of your child's weight over time.These are the weight categories pediatricians typically use:
- Underweight – BMI is less than the 5th percentile for age and sex.
- Normal weight – BMI is between the 5th and 85th percentile for age and sex.
- Overweight – BMI is between the 85th and 95th percentile for age and sex.
- Obese – BMI is greater than the 95th percentile for age and sex.
- Severe obesity – BMI s more than 120 percent of the 95th percentile values or BMI is greater than 35 kg/m^2 (whichever is lower).
For children less than 2 years old, we look at the weight-for-length ratio, (also called weight-for-height). A weight-for-length between the 2nd and 98th percentile reflects normal variation, whereas a weight-for-length less than the 2nd percentile may indicate undernutrition. Poor weight gain is also considered if there is a rate of weight change demonstrated by a decrease of two or more major percentile lines over time (eg, from 75th to 25th).
If My Child Is Underweight, What Do I Do?
Poor weight gain is common, it occurs in approximately 3 to 10 percent of children. There are many risk factors for poor weight gain that include:
- Behavioral issues
- Developmental delay
- Toxin exposures
- Medical condition that leads to inadequate intake
- Improper digestion
- Psychologic or social factors
The majority of children are underweight due to inadequate dietary intake that is behavior related. A thorough investigation with your pediatrician is necessary to determine the cause of your child being underweight in order to best identify a way to improve your child's health. The evaluation includes a complete history, where you review everything going on in your child's life at home and outside of the home. This includes daily routines, physical activity, and eating habits of your child and family as a whole. Your doctor will also do a physical examination. Laboratory and radiologic studies also may be obtained, as needed based on the history and examination.
A Few Simple Steps You Can Start with at Home:
- Start a food log and record all the items your child eats throughout the week to better understand his or her intake
- Be an observer of the behaviors demonstrated around food and meal times.
- Give healthy calories and not sugar-packed snacks. Great food choices are avocados, nuts (when age acceptable), cook with olive oil, meats, and full fat dairy.
Why is This Important?
There may be several reasons for your child being underweight. It is very important to rule out a physiologic underlying cause. Once that is ruled out, a balanced diet and daily physical activity are the key to children maintaining good health all their lives and avoiding the morbidities that being underweight can cause. You are setting the stage now for how they will live their lives and shaping the choices they will make for their future.