Almost all of us have been there. Sitting at the pediatrician’s office, the nurse wheels in the infant scale for his or her weigh-in, encircles your angel’s head with a halo-like measuring tape, marks the examination table paper at the heel and top of the head.
After gathering all the important info, they enter the information into the computer (or on a form) and scribble a number down on your progress report paperwork in their corresponding ” _____ %ile” spaces (“blank percentile”).
Maybe you’ve sat there confused. “If there was something wrong, they’d tell me…right?” you thought to yourself.
If this sounds like you, I’m here to clear it up! I’m going to walk you through reading a growth chart and interpreting the numbers.
What are Growth Charts?
First off, growth charts were made in order to track infant, child, and adolescent’s development (length, weight, and head circumference factors) from birth up to 20 years of age.
The lines show the distribution of the population according to that specific measurement.
For instance, if a measurement falls along the “75” line, then that means for that measurement, 75 percent of girls (or boys, depending on the chart) at that age/weight/length/head circumference were shorter/weighed less/had smaller head circumferences. We’ll get into that in our practice exercise below.
With this information, your pediatrician can interpret what this means for your child. The information found on the growth chart isn’t diagnostic. It’s only 1 piece of the puzzle. The info can help you and your child’s healthcare team determine where your child falls in comparison to the rest of the population in terms of growth and figure out if it’s an area of concern that needs to be addressed.
Basically it’s the info that you, as a parent, would use to say to your family “Yeah, she’s super tall for her age, she’s in the 97th percentile!” or “Yeah, she’s a little underweight compared to other babies at her height.”
There are 2 reputable organizations that publish growth charts. The WHO (World Health Organization) and the CDC (Centers for Disease Control and Prevention). The WHO growth charts are the recommended reference for 0 to 2 years old, and the CDC ones are for those 2 years and older. The CDC does not have a large enough population for a proper growth chart for 0 to 2 years, but according to the CDC, after 2 years, the WHO and CDC charts are similar.
Of note, the “WHO standards establish growth of the BREASTFED infant as the standard for growth.” They state that this is because “Breastfeeding is the recommended standard for infant feeding. The WHO charts reflect growth patterns among children who are predominantly breastfed for at least 4 months and still breastfeeding at 12 months.” (source)
There are different charts for boys and girls. This is due to different rates of growth and well, boys and girls are different in stature, proportions, etc.
Both are to be used for children in the United States (since kids in one country are different from kids in another).
Links to all growth charts can be found at the bottom of this post by clicking here.
OK – Let’s Do This!!
We’ll use Jia’s 9 month stats, as reported from her pediatrician:
Height/Length: 27 3/4 inches (50th %ile)
Weight: 17 lbs, 4 oz (23rd %ile)
Head Circumference: 44.6 cm (69th %ile)
- We will use the “Birth to 24 months: Girls Length-for-Age and Weight-for-Age” growth chart for this exercise. This is similar to the chart your pediatrician uses (it may be computerized) and keeps updated at each visit. I note the measurements we’re working with: Length (vertical axis on top half of chart), Weight (vertical axis on bottom half of chart) and Age (horizontal axes). This is what the chart looks like: (remember, this is one of two growth charts. The other one is a head circumference-for-age and a weight-for-length chart)
- I will start with the top chart. I plot the value for her length (27 3/4 inches; vertical axis) where it intersects with her age (9 months; horizontal axis), marking with a blue dot.
- Next, I plot her weight (17 lbs and 4 oz) and age (9 months) along those axes on the chart:
- Overall, the chart with her plotted points looks like this:
- Translating these points. The top half of this chart is illustrating, “What percentage of babies at 9 months are shorter than Jia?” So I look at the corresponding wavy line where her blue dot falls and look to the far right to see at approximately what percentile your little one falls:
- Translation: This means that she’s pretty average here for height at nearly 50th percentile. Meaning, 50 percent of babies her age are shorter and 50 percent of babies her age are longer/taller (she used to be in the 97th percentile, which meant she was longer compared to 97 percent of babies at the same age).
- Lastly (so I won’t bore you with showing the second growth chart), the bottom half of the chart illustrates “What percentage of babies at 9 months weigh less than Jia?” So I do the same thing as I did in step #5:
- Her lines intersect about one-third of the way between the 25 and 50 lines, so we can estimate that she’s around the 30th percentile. Translation: About 30 percent of babies at her age weigh less than Jia and 70 percent of babies at her age weigh more than her, OR you could say, “compared with other babies at this age, Jia weighs more than 30 percent of them.”
As you’ll notice, this last number is different than the stats I listed at the top of this post. The pediatrician’s database marked Jia’s progress report as 23rd percentile for weight. While it looks like using this chart she’s at the 30-35th percentile, these PDF/paper charts were last officially updated by the WHO in 2009. The computer system that the pediatrician uses are super up-to-date and percentiles may be a little different since they are more accurate, as well. Looks like 30th vs. 23rd means that comparing 2009 to present day, babies may be heavier nowadays than they used to be!
Her finished length-for-age and weight-for-age chart:
Overall Take-Home Message:
Remember, children are always growing and they grow at different rates.
These numbers are only a few pieces to the puzzle of your baby’s overall health. Observing trends in how these numbers change from appointment-to-appointment and values from your little one’s bloodwork will paint a more compehensive picture for you and your pediatrician.
If you’re concerned about the numbers you see, make sure to ask your child’s doctor. I hope that this clears up some confusion with all those percentiles you hear at the doctor’s office!
HAPPY GROWING, LITTLE SPROUTS!
WHO PDF Growth Charts* for 0 to 24 months of Age**:
*The growth charts for 0-24 months are published by the CDC but are sourced from the WHO. **The “WHO standards establish growth of the BREASTFED infant as the standard for growth.” They state that this is because “Breastfeeding is the recommended standard for infant feeding. The WHO charts reflect growth patterns among children who are predominantly breastfed for at least 4 months and still breastfeeding at 12 months.” (source)
CDC PDF Growth Charts for 2 to 20 years of Age:
Growth Charts – CDC: http://www.cdc.gov/growthcharts/
WHO Growth Charts for 0 to 24 months of Age (via CDC.gov): http://www.cdc.gov/growthcharts/who_charts.htm#The%20WHO%20Growth%20Charts
CDC Growth Charts for 2 to 20 years of Age: http://www.cdc.gov/growthcharts/charts.htm