For children, getting weighed and measured is a routine part of a visit to the doctor. Parents may notice that the nurse enters the information onto a growth chart where a little dot indicates where the child’s height, weight, and for babies, head circumference falls in relation to other children.
Usually a single measurement isn’t enough to tell us much except how one child compares to others of the same age, but after a few visits a pattern develops that can tell us a lot.
But recently I saw an article on CNN.com that reported there’s some confusion among parents about growth charts and how to interpret them. Growth charts can be a warning sign for illnesses and other health conditions, such as obesity, so I want to shed some light for baffled parents.
Understanding the chart
Pediatric growth charts have been around for many decades and were updated by the Centers for Disease Control and Prevention in 2000. They represent typical growth patterns for the wide diversity of children in the U.S. There are graphs for babies from birth to 36 months that include head circumference (the size of your baby’s head) in addition to height and weight. There are other graphs for children age 2 to 20 that only include height and weight. There are also graphs to plot BMI (body mass index), an indication of whether a child is obese or underweight, and graphs that compare the various measurements to each other.
The growth chart looks like a series of lines that move up the page in a curve. Each line within the curve represents a percentile ranking. Percentile tells us how children compare to each other. If your son’s weight is in the 10th percentile, then he weighs more than 10 percent of other boys his age (but less than 90 percent of other boys). On the other hand, if your son’s weight falls at the 95th percentile, then he weighs more than 95 percent of other boys his age.
The charts can tell us whether a child is growing at the right pace. Usually a child grows along a percentile line so a child whose height is at the 25th percentile at age 4 is usually still at or near the 25th percentile at age 6. Sometimes a doctor will become concerned when children start “crossing percentiles”-going up from the 25th percentile to the 50th percentile in a short period or going down in percentiles without explanation. By looking at the growth chart, we can detect stunted growth, sudden weight loss, extreme weight gain and concerns.
Why measure babies heads?
In babies, we check the head circumference because head growth is an indication of brain growth. As long as a baby’s head is growing steadily along a percentile curve we tend not to worry about the brain. The head does not grow well in babies with severe brain damage and so the growth chart in those babies will often reflect a head size that falls below the bottom of the curve.
A baby’s head that goes from the 25th percentile to the 50th percentile to the 75th percentile in a few visits is a red flag. Similarly, if head growth seems to be abnormally slow, some testing may be needed.
Obesity in children is becoming more common, so the BMI growth chart is something parents may want to see since it can tell when a child is overweight or obese.
Many readers already know that in adults a BMI of greater than 25 indicates a person who is overweight. In children, the normal BMI dips around age 4 when a BMI of 19 is the upper limit of normal and 20 is considered too high. After that, a “normal” BMI changes every year.