Baby growth charts, explained

What is a baby growth chart?

A baby growth chart is a tool that your baby's doctor will use to track their growth over time and compare it to other babies the same age and sex. Growth charts were developed using measurements from thousands of children.

At every doctor visit, your baby's healthcare provider will measure:

• Your baby's weight
• Your baby's height/length (measured lying down)
• Your baby's head circumference (measured around the head above the eyebrows)

The doctor will plot these measurements on the growth chart and show it to you. Depending on where the measurements fall on the chart, you can see how your baby's growth compares to that of similar babies.

Your baby's growth chart can give you a general picture of how they're developing physically, and their doctor will use it to determine whether your baby is growing in a healthy way.

But try not to get too hung up on your baby's growth chart – it's not the last word on how your baby is doing. There's a wide range of normal, and your baby's measurements don't mean they'll be short or tall, or fat or skinny, as an adult. The most important thing is that your baby is growing at a steady, appropriate rate over time.

Note: The U.S. Centers for Disease Control (CDC) recommends that doctors use the charts from the World Health Organization (WHO)Opens a new window for the first 24 months of a child's life. After age 2, doctors typically use the CDC's growth chartsOpens a new window, which are similar but based on different data.

The charts from both organizations show length in inches and centimeters as well as weight in pounds and kilograms. Both charts also use percentiles, which compare averages of children broken down by age.

How do growth chart percentiles work?

This is easiest to explain by example. If your 3-month-old daughter is in the 40th percentile for weight, that means 40 percent of 3-month-old girls weigh less than your baby, and 60 percent weigh more.

The higher the percentile number, the bigger your baby is compared to other babies the same age. If your baby is in the 50th percentile, that means they fall right in the middle of the pack.

To chart your baby's growth at home, try our growth percentile calculator.

Percentiles in a growth chart aren't like grades in school. A higher percentile isn't better, and a lower percentile doesn't mean there's anything wrong with your baby.

Let's say both parents are shorter than average, and your baby grows up to have the same stature. It would be perfectly normal for them to rank consistently in the 10th percentile for height and weight as they grow up.

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. Your child's doctor notes individual peaks and valleys, but they'll be more focused on the overall pattern of growth.

Should I worry about my baby's growth?

It could be cause for concern if your baby's percentile changes significantly. For example, if they're consistently been around the 50th percentile for weight and then suddenly drops into the 15th, your baby's doctor will want to figure out why. There could be a medical reason for the change that needs further evaluation.

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 follow your baby's growth more closely for a while.

If your baby hasn't been sick but their weight gain is slowing down while they're still growing in length, your child's doctor may suggest increasing the number of feedings. You may have to go in for more frequent visits to make sure that your baby starts gaining weight again.

There are times when gaining or losing faster than usual is a good thing. If your baby was underweight, for example, it may be a good sign that they're gaining ounces faster than growing inches.

Also, being at one end of the growth spectrum isn't always a reason to worry. For example, if your baby is very short and both parents are relatively short, then it may be perfectly appropriate for them to be in the lowest 5 percent.

But if your baby is very short and both parents are average height or taller, or if your baby is very slender and both parents are average weight or larger, then the doctor will make sure that there's no problem with the baby's growth (like a hormone deficiency or genetic problem).

Also, if your baby is in the top 5 percent for weight, the doctor will keep an eye on their growth – and possibly counsel you about their feedings – to make sure they aren't at risk for obesity.

If your baby's head measurement is much smaller than average, the doctor will make sure that their brain is growing and developing normally (a baby's brain growth is reflected in the size of their skull). If your baby's head circumference is much larger than average, they'll be further evaluated to make sure that they don't have excess fluid in the brain, a condition called hydrocephalus.

How much does birth weight determine future growth?

Birth weight seems to matter less than you might think. Genes, not newborn weight, generally determine 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 you and your partner tall, short, or average? Slender, heavy, or medium? Chances are, your child will be similarly built as an adult.