By Nancy Gottesman
Eleven years ago, when my son was a 2-year-old, I asked our pediatrician which percentile he fell into. I suspected he was large for his age and wanted to hear the number so I could be the proud parent of a “90 percentile” baby. Her reply, however, startled me. “He’s perfectly healthy and he’s thriving,” said the doctor. “What do you care how he compares to 10,000 white kids in Ohio?”
She did end up telling me, of course, but her point was a good one: If we know our kids are growing and developing on track, why do we look upon those pediatric percentiles as some sort of report card? “Parents need to understand that everything between the 3rd and 97th percentiles is normal,” explains David Wolfson, M.D., medical director of Children’s Community Pediatrics, which is affi liated with Children’s Hospital of Pittsburgh of UPMC. “Growth charts are an important diagnostic tool, but the actual percentile number may be the least important part.”
What is a percentile?
In 1977, the Centers for Disease Control (CDC) developed growth charts as a clinical tool for health professionals to determine whether a child was developing adequately. After collecting thousands of U.S. children’s height and weight stats since the 1960s, the CDC was able to show a range of measurements on one chart, using a curved line to represent a percentile.
In 2000, the charts were revised to include BMI measurements and to reflect changing ethnic populations in the U.S. “When the charts were initially devised, they were based on middle-class white kids,” says Katrina Parker, M.D., director of pediatric endocrinology at the University of Texas Medical Branch in Galveston. “Now the charts represent today’s population better.” Your pediatrician uses different sets of growth charts based on your child’s age and gender.
One set of growth charts covers babies and toddlers from birth to 36 months, since they grow at a different rate than toddlers and older kids. Another set covers kids 2 to 20 years old. Still another set of special growth charts are used for children with health conditions such as Down’s syndrome. And in each age or health category, there is one set of charts for boys and one for girls because the genders grow at different rates.
At your annual well-child checkup, your doctor will plot your child’s height and weight along one of the curves on the appropriate growth chart. This plotting determines the percentile that shows where your child’s measurements fall when compared to others. The higher the percentile, the larger the child in comparison to other kids of the same gender and age. The lower the percentile, the smaller the child. For instance, a 3-year-old girl whose weight is at the 25th percentile weighs the same or more than 25 percent of girls her age and less than 75 percent of them.