Charting a child’s height, weight, and head circumference over time also allows doctors and parents to see if a child is gaining weight more quickly than they are adding inches, or vice versa—signs that they may be on track to becoming overweight or aren’t eating as much as they should. It is not the actual percentile number that is important. What your child’s pediatrician is tracking is how your child’s growth is changing over time. Are they following their curve, indicating healthy growth? Or is there a change in their growth pattern, which could be a sign of a problem?
Understanding Percentiles
When your child’s doctor measures height, weight, and head circumference, not only will they tell you the results in terms of inches and pounds, they will also express what your child’s percentiles are for each measurement. The percentile number means that your child exceeds that percentage of children their age for that measurement. However, weight charts do not reflect the obesity epidemic. About one-third of kids are now overweight, meaning that there are many more than 5% of kids above the 95th percentile for weight. The growth curves haven’t been adjusted as the intended purpose of the growth charts is to plot out what is typical, healthy growth.
Growth Patterns
It is important to understand that growth charts are best used to follow the rate of your child’s growth over time. Plotting your child’s weight and height at different ages and seeing if they follow a consistent growth curve is more important than what their percentiles are at any one time. Even if your child is at the fifth percentile for weight (meaning that 95% of kids their age weigh more than they do), if they have always been at the fifth percentile, then they are likely growing normally. It would be concerning and it might mean there was a problem with their growth if they had previously been at the 50th or 75th percentile and had now fallen down to the fifth percentile. Children between the ages of 6 and 18 months can normally move up or down on their percentiles, but older children should follow their growth curve fairly closely.
Charting Your Child’s Growth Yourself
If you’d like to keep an eye on how your little one is growing between doctor visits, you can find growth charts online to help you do that. The first step is to find the right chart. If your child is healthy and developing typically, you have a couple of choices depending on her age. For an infant or toddler (up to age 2), use the growth charts from the World Health Organization (WHO), which reflect an international standard that was developed in 2006. If your child is 2 or older, look at the growth charts developed by the National Center for Health Statistics. These were updated and revised by the U.S. Centers for Disease Control and Prevention (CDC) in 2000. Note that there also are growth charts for premature babies and children who are born with specific conditions, such as Down syndrome, Prader-Willi syndrome, achondroplasia, Marfan syndrome, and others. The Magic Foundation offers specialized growth charts for children with Noonan syndrome, Turner syndrome, Russell-Silver syndrome, and more conditions.
How to Read Growth Charts
Say you have a 2-year-old boy who weighs 30 pounds. To find out what his percentiles are, start by using the CDC growth chart for boys from birth to 36 months. This chart, like all the others, has the age at the top and bottom of the grid and length and weight at the left and right of the grid. Curves on the chart indicate the percentiles for length-for-age and weight-for-age.
Step 1: Find the child’s age at the bottom of the chart and draw a vertical line on the growth chart (from top to bottom). For this example, you would draw a line through 24 months (2 years).Step 2: Now find the child’s weight on the right-hand side of the chart, 30 pounds in this example, and draw a horizontal line (from left to right).Step 3: Find the spot where these two lines intersect or cross each other.Step 4: Find the curve that is closest to this spot and follow it up and to the right until you find the number that corresponds to your child’s percentile.
In this example, a 2-year-old boy who is 30 pounds is at the 75th percentile for his weight, meaning that in a population of children growing optimally, he weighs more than about 75% of boys his age. Finding a child’s percentile is a little harder if the curve doesn’t actually pass through the spot where age and weight come together. For example, if the boy in the example weighed 31 pounds, you would use all of the same steps but also have to imagine a curve that is somewhere between the 75th and 90th percentiles, figuring that he was at about the 80th to 85th percentile. You can use the same steps to plot your child’s height and body mass index (for kids ages 2 and up).
