Infant Growth Charts: How Pediatric Care Providers Measure Your Baby’s Growth Without BMI

BMI is not recommended by the CDC as a health measurement tool for babies younger than 2 years old.

Until your baby turns 2, infant growth charts like this one for boys and this one for girls, are what’s used to evaluate your baby’s progress. Pediatric care providers measure a baby’s height, weight, and head circumference and input those numbers to the correct infant growth chart for your child’s gender. The infant growth charts are further broken out by month of age. The chart is expressed through percentiles, or the typical distribution of heights, weights, and head circumferences of children by age and gender.

The pediatric care provider will see what percentile your child’s weight, height, and head circumference each fall into and record your child’s growth.

• In general, higher percentiles mean he’s big for his age.
• Lower percentiles mean he’s smaller than other boys in his age group.

Pinpointing a “normal” range for a baby’s growth isn’t as simple as a number value. Babies go through brief periods when they stop gaining weight, gain a lot of weight, or even lose some. Because a baby’s body is constantly growing—in height, weight, and yes, even head circumference!— his absolute numbers change week to week. To account for this zigzag of growth, pediatric care providers use percentiles so babies can be compared to other babies in their month of age and gender rather than trying to hit a specified number to indicate “normal.” After all, the only thing that’s normal for babies is change!

When it comes to your child’s health in the context of weight and height, it’s more important to keep an eye out for these warning signs:

• Your baby’s growth patterns change dramatically – If your little one’s height and weight both have been growing at the same rate in the 43rd percentile but suddenly both shoot to the 80th, it may be worth talking to your pediatric care provider about this change.
• Your child’s weight percentile changes at a different rate than his height percentile, or vice versa – If your baby gains in either height or weight percentile, but the other metric is falling behind, this could be a cause for concern.

Because of the continuously changing shape of your baby, the most important thing a pediatric care provider will look for is growth in general. The trend of growth is far more important than a baby’s position on the growth chart. That’s why infant growth charts are preferred over BMI—they take into account your baby’s natural growth and can ensure your child is on track for healthy growth and development.

Plus, infant growth charts give parents an early warning to put fragile things on higher shelves!

Measuring BMI Once Your Baby Turns Two

Once your baby turns 2, your baby’s growth patterns start to settle a bit. At this stage, doctors start measuring weight, height, and BMI to gain an understanding of your child’s health.

What is a normal BMI for children? BMI stands for body mass index and it is a way to estimate how much body fat someone has by dividing an individual’s weight (in kilograms) by the square of their height in meters. This calculation results in a number called the BMI, which can then be used to determine what weight status category somebody falls in.

A child’s BMI will be compared to a BMI percentile of other children of the same age (by year this time) and gender, using BMI percentile charts this this one for boys and this one for girls. For example, if your child is a strapping 4-year-old with a BMI in the 82nd percentile, that means that her BMI is higher than 82% of other 4-year-old girls.

The BMI percentile categories and health values are:

• Underweight – If your child is in less than the 5th BMI percentile for her age group.
• Healthy weight – If your child is between the 5th to 84th BMI percentile.
• Overweight – If your child is between the 85th and 95th BMI percentile.
• Obese – If your child is above the 95th percentile.

A child’s BMI is considered “normal” when it falls within the 5th or 85th percentile. That’s quite a range! Why such a large range? Because even though they’ve grown out of their super-growing baby days, children are still experiencing periods of growth spurts and body changes. Kids grow at different rates, particularly during childhood or puberty, which is precisely why percentiles are used until the age of 20—it helps pediatric care providers and healthcare providers understand a child’s health within the context of other children like her. BMI by itself isn’t enough to glean a full picture of your child’s wellbeing.

Why do healthcare providers stop using percentiles at age 20? At that point, adolescents have gone through all their growth spurts and BMI can be used to evaluate one aspect of health without the need for percentiles. Age, (head circumference!), and even gender will no longer factor into the equation.

It’s important to note that the percentile your child falls in isn’t like a report card for health. Having a high percentile doesn’t mean that your child is at the head of the pack and having a low percentile doesn’t mean she needs to increase her PB&J intake.

While BMI measurements can be a good screening tool for potential risks, it’s just one part of the equation of your child’s health. How quickly children grow also depends on a number of variables, such as their genetics, hormones, body structure, and elements from their environment.

That said, if your child’s BMI registers on the higher end of the percentiles, you might be worried about her long-term health. Just keep an eye on the general trend of growth and talk to your pediatric care provider if you’re worried about your child’s development or BMI.

How do genetics play into BMI?

The research on genes related to BMI is continuing to develop and grow. Studies have so far looked at more than 50 genes and variants that might contribute to a child’s BMI. That means that if your baby boy has some of these genes and lives in an environment that doesn’t promote a healthy and active lifestyle, he may have an increased risk for childhood obesity.

Some of the genes linked to BMI include:

• The LEP gene – Mutations of the LEP gene causes congenital leptin deficiency. Leptin is a hormone that regulates body weight by signaling when you’ve eaten enough. The absence of that means that the body doesn’t feel satiated, leading to overeating and a higher BMI than is considered healthy.
• The ADIPOQ gene – This gene instructs your body to make adiponectin, a hormone that helps burn fat. Variants of the ADIPOQ gene can lead to a reduction of adiponectin, which means less efficient fat burning and a greater risk of an unhealthy BMI. Healthy habits like regular exercise and a nutritional diet can help boost your adiponectin levels.
• The FTO gene – FTO promotes food intake, and the gene most consistently associated with obesity. This review of over 200,000 adults and 19,000 children with the FTO gene shows that physical activity reduces the risk of obesity, which reemphasizes the importance of an active lifestyle.

No gene on its own can definitively cause a particular BMI, but the cumulative result of all the different genes in play can provide a useful overview of the risk.

Knowing whether your child is at risk for high BMI can help you create a supportive environment around food and exercise so you can ensure healthy growth and development for your little one.

In conclusion, while baby BMI is not applicable until the age of two, monitoring your baby’s growth through infant growth charts is crucial for understanding their health status and development. It is essential to remember that each baby grows at their own pace, and factors such as genetics, nutrition, and environmental elements can influence growth trends, so a broader understanding of a child’s health, rather than focusing on BMI alone, ensures the most accurate assessment.