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Decoding Percentiles: How To Understand Infant Growth Charts

by Vannessa Rhoades 21 Jun 2024
Decoding Percentiles: How To Understand Infant Growth Charts

Parenting comes with its own set of adventures, and one big checkpoint is keeping tabs on your little one's growth and development. Understanding those infant growth charts is like deciphering a roadmap for your baby's well-being. We’ve put together a friendly guide to help unravel the mysteries of infant growth charts—breaking down what they measure and how to read them, arming you with the know-how to navigate these charts like a pro on your parenting journey.

What is an infant growth chart?

An infant growth chart, or infant growth spurt chart, is a tool that allows you and your pediatrician to monitor and assess your baby's growth. Comparing their growth with that of other babies of the same age is a valuable indicator of your baby's overall health and nutritional well-being. A growth chart documents changes in your baby's measurements, such as length (height), weight, and head circumference. These measurements are plotted on the chart, illustrating their progression over time. The vertical axis represents the measurement, while the horizontal axis corresponds to the child's age. 

Growth chart averages are based on extensive measurements of thousands of children, establishing national average weights and heights for each age and gender. The lines or curves on these charts indicate the distribution of children's weights at specific ages. For instance, the 50th percentile line represents the weight at which half of the children in the country weigh more, while the other half weigh less. For infants aged 0 to 2 years, growth is typically assessed using standards set by either the World Health Organization (WHO) or the US Centers for Disease Control (CDC).

What do infant growth charts measure?

During each well-child visit, your child's provider will assess the following:

  • Weight, measured in ounces and pounds (or grams and kilograms).
  • Height, measured while lying down for children under age 3 and standing up for children aged 3 and older.
  • Head circumference, measured by wrapping a tape around the back of the head above the eyebrows.

Starting at age 2, the child's body mass index (BMI) can be calculated using height and weight to estimate body fat. These measurements are plotted on the growth chart and compared to the standard range for children of the same sex and age, with the same chart used as your child grows older.

How do you read an infant growth chart?

Understanding your child’s growth patterns can be a bit confusing if you’re seeing this information for the first time. Let’s take a closer look at how to interpret this information.

  1. Locate your child's age at the bottom of the grid and draw a vertical line at that point.
  2. Find your child's measurement on either side of the grid and draw a horizontal line at that point.
  3. Mark a dot where the two lines intersect.
  4. Identify the curve closest to the dot, follow it up to the end, and note the number at the end of the curve—this is your child's percentile rank for weight, height, length, or whatever measurement you happen to be evaluating.
Decoding Percentiles: How To Understand Infant Growth Charts
Decoding Percentiles: How To Understand Infant Growth Charts

How do you interpret growth percentiles? 

Now that you have your child's growth chart, it's time to interpret the measurements. The chart typically features age at the top and bottom, with length, weight, or other measurements along the left and right sides. Curved lines represent percentile numbers, indicating patterns of growth.

A percentile number signifies that your child's growth exceeds that percentage of others their age. For instance, if your child is in the 75th percentile for weight, this means that they weigh more than 75% of children the same age. The important thing to remember is that your child's position on the chart matters less than whether they are following the curved lines, signifying healthy growth over time.

What is a good percentile for baby growth?

Being in a high or low percentile doesn't necessarily indicate a child's health or suggest growth or weight issues. The percentile number is not the primary focus for pediatricians; instead, they aim to ensure that your child is growing at a healthy rate. Healthy children come in various shapes and sizes. A baby in the 5th percentile can be just as healthy as one in the 95th percentile. Ultimately, your child's pediatrician is the best resource for tracking health and growth. If you have any concerns or questions regarding your child's weight or height, your pediatrician is equipped to provide the answers.

Decoding Percentiles: How To Understand Infant Growth Charts

What does a growth spurt in an infant’s chart mean?

Parents often feel concerned if their child's height, weight, or head size falls below or above the average for their age, fearing potential impacts on academic performance or sports participation. However, understanding why your child may be above or below average may help ease some of your worries:

  • Measurement errors may occur, such as when a baby squirms on the scale.
  • A single measurement may not reflect the overall picture; temporary factors like illness can affect weight.
  • There's a broad range of what is considered "normal," and a lower percentile doesn't necessarily indicate sickness or inadequate feeding.
  • Child measurements don't predict adult characteristics like height or weight.

That said, certain changes on the growth chart may raise concerns, according to the National Library of Medicine:

  • Persistent measurements below the 10th or above the 90th percentile.
  • Abnormal head growth rates over time.
  • Inconsistencies, such as a significant drop in percentile over several months.

Certain anomalies on the growth chart may signal a potential issue, and your provider will assess whether it indicates a medical problem or requires close monitoring.

Where can I find an infant growth chart calculator? 

You can find growth charts for infants and older children on the World Health Organization (WHO) website and the website of the US Centers for Disease Control (CDC).

Disclaimer: The information on our site is NOT medical advice for any specific person or condition. It is only meant as general information. Please contact your health provider if you have any medical questions or concerns about your child or yourself.

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