How To Interpret Growth Curves

One of the most important parts of the well visit is the growth curves. A 10-second review of growth curves tells the pediatrician volumes of information. Hopefully, by the time you finish reading this article, you’ll feel like an expert at interpreting growth curves as well.

The growth curves are the little graphs that tell you where your child stacks up size-wise compared to other kids the same age. Now, there are different graphs for boys vs. girls, and different graphs for different countries. It makes sense when you think about it; average kids in China are generally smaller than the average kids in the United States.

What are the different curves?

Younger than 2 years-old:

1. Height: Measured from the top of the head (with the chin in neutral position) to the bottom of the heel. In our office, we lay a young child down on a paper-lined table and make the marks with a pen. We then move the child and measure the distance between the two marks.
2. Weight: A more sensitive infant scale is typically used in the younger age groups.
3. Head Circumference: Measurement around the head (going across the forehead and temples and kept perfectly level).

Older than 2 years-old:

1. Height: Usually measured with a child standing, without shoes, heels against the measuring wall, and chin level.
2. Weight: Typically taken on a standing scale.
3. Body Mass Index (BMI): A mathematical calculation of the body mass divided by the square of the body height. It essentially tells you if your child is overweight, underweight, or just right.

What do the numbers mean?

The numbers tell you where your child’s size is in relationship to other children. Average is 50%. So anything above 50% reflects being bigger than average and anything below 50% reflects being smaller than average.

It is super important to consider the numbers in relationship to each other. If the numbers (height, weight, and head circumference—if under 2 years-old) are all similar in value, then your child is relatively proportionate. If the numbers are vastly different, then it may reflect a bigger problem.

How do you know if there is a problem?

1. Children tend to grow a steady rate. If any single curve (height, weight, or head) changes percentiles dramatically (either up or down), then something is wrong. For example: If a child has been growing around the 30% for height, weight, and head, but then comes in with a head measurement of 95%, there is likely something happening in that head or brain (e.g., a mass/tumor, or too much fluid). As another example, consider a child who has been growing at the 70% for measurements. If the next visit, the child’s weight is down to 20%, something is likely wrong (e.g., a metabolic problem, family stress, food insecurity, etc.).
2. Differences between curves. Generally, children grow proportionately. If one of the curve measures is off, that can indicate a problem. For example, if the height and weight are 25%, but the head is 85%, then the child has a disproportionately large head which may warrant further workup to determine if there is a problem (more than just a genetically big head). As another example, consider the child who is 97% for height and 15% for weight. That is a very thin child. One must consider whether a metabolic problem exists? Is the child getting enough to eat? If on the other hand, the child is 55% for weight and 3% for height, the child also has problem. At first blush, it may be easy to think that the child is ok (average weight), but the child isn’t tall enough to support that weight. In that case, the child is overweight. The pediatrician will consider if the child is eating too much, not active enough, or has some underlying metabolic issue.
3. Not genetically appropriate. When looking at growth curves, one must always consider the child’s genetic potential. If the parents are 4 ½ feet tall and weigh 80 lbs., I expect a tiny child. A huge child coming from those parents may indicate an excess of growth hormone (which can come from tumors). When I was in residency, there was a child who had a growth hormone deficiency despite being in the 75% for height and weight. The child’s dad was over 7 feet tall and mom was 6 ½ feet tall. The deficiency was detected based on the growth curves. Even though the child was bigger than average, the child was not nearly as tall as one would expect for his genetic potential.

Now the next time you are at a play-group and some parent is boasting about their child who is in the 75% you’ll know what they are talking about.