How a Registered Dietitian Interprets Pediatric Growth Charts
3 Simple Steps
Pediatric growth charts are tools to help us figure out if a child has a healthy weight. Pediatric growth charts consist of a series of percentile curves that illustrate the body measurements in children. There are different growth charts available for infants and children. The World Health Organization (WHO) and the Center for Disease Control and Prevention (CDC) have developed growth charts for parents and doctors to use as tools to monitor children’s growth and development.
Growth Charts for Children Under 2 Years of Age
There are two sets of growth charts for children under 2 years of age. One set is for boys and the other one is for girls. To find out whether the child has a healthy weight, we use the weight-for-length chart, not the weight-for-age chart. Below are the definitions of weight status for children under two years of age:
Underweight is defined as a weight-for-length at or under 5th percentile.
Normal weight is defined as a weight-for-length over 5th and under 85th percentile.
Overweight is defined as a weight-for-length at or above the 85th percentile and lower than the 95th percentile.
Obesity is defined as a weight-for-length over the 95th percentile.
3 Simple Steps
There are three simple steps to find out whether your child (birth to 2 years of age) has a healthy weight. First, you select a right growth chart based on the gender of your child. Second, you simply plot the child’s height and weight measurements on the growth chart. Third, compare the plotted dot to the definitions of weight status shown above.
For example, an 18-month old girl, Nancy, weighs 29 pounds and 8 ounces and has a length of 33 inches. Below is how her weight-for-length growth chart looks like:
Growth Charts for Children Over 2 Years of Age
There are two sets of growth charts for children over 2 years of age. One set is for boys and the other one is for girls. To find out whether the child has a healthy weight, we use the Body Mass Index (BMI)-for-age chart, not the weight-for-age chart.
Body Mass Index (BMI) for most people is a reliable index of body fatness. The BMI is calculated from height and weight. Here is the BMI formula:
Formula: weight (lb.) / [height (in)]2 x 703
For children older than two years of age, we use the BMI-for-age percentile to monitor whether the child has a normal weight. Instead of doing your own calculation of BMI, you can visit the Center for Disease Control and Prevention (CDC) website. On the web page, you can enter your child’s age, gender, height, and weight to get the BMI value and the BMI-for-age percentile. A child’s weight status is defined based on the BMI-for-age percentile, not the absolute number of BMI. Here are the definitions of weight status using the BMI-for-age percentiles for children (2–18 years of age):
Underweight is defined as a BMI at or under 5th percentile.
Normal weight is defined as a BMI over 5th and under 85th percentile.
Overweight is defined as a BMI at or above the 85th percentile and lower than the 95th percentile.
Obesity is defined as a BMI over the 95th percentile.
3 Simple Steps
There are three simple steps to find out whether your child ( over 2 years of age) has a healthy weight. First, you select a right growth chart based on the gender of your child. Second, calculate your child’s BMI using the formula listed earlier in this article or use a CDC calculator. Third, plot the child’s BMI on the BMI growth chart or see the results on the CDC BMI calculator website.
For example, for a 3-year-old boy who is 4 feet tall and weighs 50 pounds, here is how the report will look like on the CDC website for this child:
Based on the height and weight entered, the BMI is 15.3, placing the BMI-for-age at the 24th percentile for boys aged 3 years 0 months. This child has a healthy weight.
How to Interpret Pediatric Growth Charts
Each child grows at different pace. Therefore, each one has his or her own unique growth chart curve. It is very important to compare the child’s current measurements with the previous ones.
Let’s look at the following example:
A 7 year old boy, Jack, weights 38.5 lbs. with a height of 44.5 inches. When I entered his information at CDC BMI calculator, the results looked like these:
Based on the height and weight entered, the BMI is 13.7, placing the BMI-for-age at the 4th percentile for boys aged 7 years. This child is underweight and should be seen by a healthcare provider for further assessment to determine possible causes of underweight.
When I compared Jack’s current measurements with his previous measurements taken at 6 years of age, it gave me a completely different picture. Based on his growth charts shown below, all of his growth chart curves were moving upward and these upward curves indicated that Jack is now growing well and has shown some “catch-up” growth.
For more information on how to interpret your child’s growth charts, please consult your doctor or a registered dietitian.
