Q: What do the percentiles mean on a growth chart for babies? When is a drop a concern?

A: When you visit your healthcare provider, your child’s height, weight and head circumference (in the first two years) are generally measured. These are then recorded on standard growth curve chart, which shows the range of normal in percentile lines for every week of life. So if, for example, your child plots on the 50th percentile, then it means that he weighs or measures pretty much the average for the North American Caucasian population from which the charts were derived. If he plots on the 97th percentile, then it means that he is the 97th heaviest or tallest out of 100 children of similar age, and by contrast if he is on the third percentile then it means he is the third heaviest or tallest out of 100. Importantly both of them are likely entirely normal as weight and height are dictated mainly by family genetics, nutrition, etc.

Look for these things: first, that your baby is growing proportionately (i.e., weight is appropriate for length), and second, that he is growing at the expected rate typically following along the same percentile curve. Deviation from these expectations may mean that your child is simply expressing his own unique growth pattern, but generally a drop (or gain) of two percentiles rankings—for example, from 97th through the 75th to below the 50th percentile curve—will likely result in a thorough review of nutrition and health to ensure that there are no health or nutritional causes for this change.

For more advice from Dr. Friedman, be sure to check out these questions:
• How Do I Prevent My Child from Getting Head Lice?
• What Are the Signs of Celiac Disease?
• Does My Child Need More Sleep?
• What’s the Best Age to Get My Kids Tested for Allergies?