Growth charts: Understanding the results
What can my baby's growth chart tell me?
Your baby's growth chart can give you a general picture of how your baby is developing physically. By comparing your baby's measurements — weight, length, and head circumference — to national averages for children of the same age and sex, and to measurements from previous checkups, the doctor can determine whether your baby is following a healthy overall growth pattern.
Don't get too hung up on your baby's percentiles, though. While the current growth charts (released in November 2000 and based on data from the National Center for Health Statistics, U.S. Public Health Service) are a vast improvement over earlier charts, they're not the last word on how your baby is doing. The most important thing is that your baby is growing at a steady, appropriate rate, not that he's hit some magic number.
You can see the charts themselves on the Centers for Disease Control and Prevention Web site.
What does "percentile" mean?
It's easiest to explain this by example. If your 3-month-old son is in the 40th percentile for weight and the 80th for height, for instance, that means 40 percent of 3-month-old boys in the United States weigh the same as or less than your baby and 60 percent weigh more. Similarly, 80 percent of boys his age are the same length as or shorter than your child and 20 percent are longer. To chart your baby's growth at home, try our growth percentile calculator.
My baby is only in the 25th percentile. Isn't that small?
If your baby has always hovered around the 25th percentile in both height and weight, your doctor won't be concerned that 75 percent of boys his age are bigger than he is. What's important to remember is that your doctor is watching how your baby grows, not just how much.
Babies tend to go through rapid growth spurts, during which they might put on a little extra weight or length. Other months they may grow only a fraction of what they normally do. While the doctor will note individual peaks and valleys, she'll be most concerned with the overall pattern of growth.
When should I worry?
You should be concerned if your baby's percentile changes significantly. For instance, if he's consistently been around the 50th percentile for weight and then drops into the 15th, your doctor will want to figure out why. She'll consider whether there could be a serious medical reason for the change that needs further evaluation. Of course, a minor illness or a change in your baby's eating patterns might result in a smaller drop, in which case the doctor may just want to follow your baby's growth more closely for a while.
If your baby hasn't been sick but his weight gain is slowing relative to the curve he's been on (all babies tend to have faster growth in the first few months and then a relative slowing and flattening of the curve), your practitioner may suggest increasing feedings. You may be asked to come in for more frequent visits to make sure that your baby starts gaining weight again.
Generally, doctors will look more closely at babies who fall in the extreme percentile ranges — above 95 percent and below 5 percent — in any area. Sometimes extreme measurements are no cause for concern.
If your baby is very short and both of his parents are unusually short, for example, then it may be perfectly appropriate for him to fall in the lowest 5 percent range. But if your baby is very short and both of his parents are of average height or taller, or if your baby is very slender and both his parents are of average or larger than average weight, then the doctor will want to make sure that there's no problem with his growth (like a hormone deficiency or genetic problem). On the other hand, if your baby is in the highest 5 percent range, the doctor will watch his growth — and possibly counsel you about his feedings — to make sure he isn't headed for obesity.
Of course, there are times when gaining or losing faster than usual is a good thing. If your baby was underweight, for example, it may be great that he's increased his usual curve.
If your baby's head measurement is much smaller than average, the doctor will want to make sure that his brain is growing and developing normally, since your baby's brain growth is reflected in the size of his skull. If his head circumference is much larger than average, she'll further evaluate him to make sure that he isn't suffering from a dangerous condition called hydrocephalus (excess fluid in the brain).
How much does birth weight determine future growth?
Birth weight seems to matter less than you might think. In general, genetics, not newborn weight, determines adult size. Petite babies sometimes grow to be strapping adults and large babies can become slender over the years. A baby's parents are the best indicator — are they tall, short, or average? Slender, heavy, or medium? Chances are the child will be similarly built as an adult.
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