I know you know what I’m talking about – something moms in particular love to talk about is their baby’s growth. Sometimes it’s pride:
“They weigh ____ lbs now!”
Or they are “_____ cm tall!”
The other side of it is worry.
“My baby is only in the ____ percentile, do I need to be worried about their growth?“
I think percentiles can be confusing for parents. For whatever reason, lower number percentiles seem to have negative connotations in our minds. I have a good understanding of how a growth charts work and yet I still fell victim to this type of thinking.
*Disclaimer: This blog is intended for informational purposes only. The information on this blog should not be used as a substitute to medical advice or medical treatment. As always, your Primary Care Provider, a doctor, or another health professional is your best resource for specific questions and medical advice. If you believe you or a loved one are experiencing a medical emergency, please contact 911.*
Part of the confusion is, I think, because we associate growth with bigger and/or increasing numbers – which isn’t incorrect, it just doesn’t necessarily apply in the same sense to percentiles. The other part of it is because with things like grades or SAT scores for example, a higher percentile is “better” (I put that in parentheses because tests or school are not a great way to compare or define people). So it is simply logical to think that growth charts would work the same way.
But they don’t. Let’s look at growth charts and a bit into development to understand why you don’t normally need to sweat over a percentile being “higher”. If your doctor or provider tells you that your baby is growing well (and you see your baby thriving), that is what matters most.
First of all, what is this growth chart you talk of?
You more than likely have seen a growth curve before, whether it be professionally, as a result of having a child, or in a math class for example. Actually, they’re all over the place – I’d be surprised if you hadn’t seen one at some point in your life. Remember X and Y axes? Yeah, you know what I’m talking about – it’s a graph of growth!
In Canada we use the WHO growth charts which were tailored specifically for us and our population by some of our healthcare professionals – that includes dietitians, family physicians, paediatricians, pediatric endocrinologists, and nurses! These are the charts I will be linking to and referring to specifically in this post, however I’ve included a link just below to the CDC charts as well.
The USA also uses the WHO growth charts for children up to age 2. After age 2 they switch over to the CDC developed growth charts. Both of these are of course adapted to be reflective of growth, nutrition, and development in the USA.
Without going too many specific details about the charts and their development, know that the Canadian adaptation is based on the growth and development of breastfed babies and that the sample is considered lighter and taller. The Canadian growth charts are also representative of the growth of multiple ethnicities as the data set that is used to make the charts comes from multiple locations (so this should be comparable to the 0-2 charts for the US).
There are charts for girls and boys, since their growth and development differs. The charts are also divided into different age groups or periods, 0-24 months and 2-19 years. Within these categories there are also different curves – for 0-24 months you see one chart for weight/length and one for weight for length and head circumference (all the measurements your baby has taken at their appointments). From 2-19 years there is height/weight and BMI.
The WHO charts can be used for preterm infants, low birth weight infants, and with infants and children whose growth and development may be impacted by a medical condition – however, it is suggested that they can be used in conjunction with a growth chart specific for their situation. So for example, if your baby was born before 37 weeks gestation, they may use Fenton’s preterm growth chart at the hospital or in the NICU, then switch over to the WHO charts in a primary care setting (your doctor or paediatricians office) and factor in your child’s corrected age.
So how are growth charts used?
When you take your baby in for a “Well Baby” appointment with their physician (whether that be your GP or a paediatrician), they always measure their growth. They may also measure their growth at in-between appointments – but not always. It depends on the reason for visit, however if medication is going to be prescribed for a little one, a weight is a must since most medications are weight-based for the paediatric population. It is also recommended that growth be checked at every appointment for children.
What doctors are looking at here is often not the “one-time” measurement, but the trend over time. Ahh yes, the trend over time. I feel like I talk about this a lot lately because of the pandemic since the same idea applies to watching positive case counts for example. We need to see how the data changes over time to make an accurate interpretation. A single measurement is not very useful for the purpose of drawing conclusions.
So, you go in for your appointment and measurements are recorded – for young babies it is weight, length, and head circumference.
For the purpose of this post I won’t be looking very in-depth at head circumference, but it is also a way of tracking a baby’s growth. Perhaps I’ll do a post in the future on ‘why the hell they need to put a measuring tape around my child’s head’ at every appointment!
Your child’s measurements are then plotted on a graph, most of the time now this will be on the computer in their electronic medical record (though some places may still be using paper records…). At each well baby appointment (2, 4, 6, 9, 12 months in the first year usually – you may see your doctor in between as I mentioned – this could be for a weight/growth check or an entirely different reason like a cold or other concern) they do this – check their measurements and plot them on this graph. The birth measurements should be on there too from the hospital or midwife as a starting point.
After a few points have been added to the graph, we can observe the “trend“. What we usually see is our child’s weight and height, for example, following along a percentile curve.
Ok stop. What is a percentile?
This is where I think there is a lot of confusion, because as I mentioned before in other situations a higher percentile is often interpreted as good, while a lower percentile can be “bad”.
This is not the case in child growth measurements.
A percentile is simply indicating where your child falls in comparison to other children, whose data was captured to create the growth curve. Remember how I was saying the charts are based on real data from breast-fed babies of multiple ethnicities? This is what your child is being “compared to”, and this is meant to be representative of the population of your country or area.
So, if your child is in the 50th percentile for length, that means that 50% of children are longer and 50% of children are not as long as your child. Being at a certain percentile isn’t the goal, but seeing growth along the same (or close to the same) percentile is the trend we are looking to see.
It can be normal and expected for a slight shift in percentiles (1-2 percentile curves) to happen anywhere within the first 3 years of life, and you may see this again during puberty. What we don’t want to see is a sudden drop and then a trend downwards, or a flattening line with no signs of growth over time. This could indicate an abnormality or an issue that should be addressed – that is why taking your baby to their regular well baby checks (and your child to their physicals) is super important!
Still, all changes in a growth chart will also be considered within your child’s health, lifestyle, and family history. Breastfeeding and formula feeding for example, can make a difference; and so can things like your personal growth history. A growth chart on its own may indicate an area of concern but all concerns need to be considered alongside factors like these that may impact growth and development (or expected growth and development).
Will a breastfed baby grow very differently than a formula fed baby?
Based on the data, maybe. Babies who are breastfed on average show increased growth before they are 6 months and then a stabilization. So the charts may interpret formula fed babies as smaller early on (because again, the data the charts are made with is from breastfed babies who tend to grow faster in the early months) and potentially larger after the 6 month mark.
Again – this will be examined in context. Your doctor should be asking you at each appointment how you are feeding your baby. You may be doing one or the other, or both! All of this should be considered alongside any growth measurements.
It is also important to remember that every baby is different and will grow differently. So your baby, no matter how they fed, will grow how they are meant to grow and this may be slightly different than what is “expected” or average.
What are the criteria for under and overweight babies?
All measurements must be considered within context.
Less than the 3rd percentile or greater than the 97th percentile would be underweight or overweight cut-offs respectively for babies that are less than 2 years old in Canada (based on weight and age, and weight and length). It may warrant further investigation however it should also be considered within context and your doctor will ask you the appropriate questions and may have you come in for interim visits if necessary or if they are concerned. They may make a referral to another specialist or allied health professional if needed.
Your child may still be experiencing normal growth for them, but they may need additional follow up or a referral based on your doctors assessment.
The Dietitians of Canada guidelines states that the cut-offs for babies under 2 years are extra cautious. You can see the other cut-off measurements on this page.
Keep in mind that accuracy of measurement is something that is not always achieved.
If you’ve ever taken your baby for a well baby check (or multiple) – you may notice that it can sometimes be challenging to measure them, especially as they grow. And let me tell you it doesn’t get any easier when they are 2+ years necessarily.
Some kids hate standing on the scale. Babies don’t like to stretch out for their length measurements. Head circumference is… challenging. We can fall victim to both human error and technological errors when it comes to these things. So there are a lot of challenges to getting a 100% accurate measurement – that is why everything is considered within context.
If there is a concern, your doctor may ask you to come in before your next well baby or physical to check weight or height (or head circumference as applicable) in the interim. From that follow up appointment it is sometimes revealed that there was an error in measurement at some point and you move on with your life. If that is not the case – then it was caught and it is being addressed which is what matters most.
If you are a healthcare professional working in a primary care setting in Canada with children, check out the Dietitians of Canada handout which includes the guidelines for measuring children accurately.
- Every child grows differently – it’s important not to compare your child’s growth with another child’s (even their sibling!).
- Take your children to their well baby appointments and physicals as it is important to monitor growth and development over time
- One measurement is often not indicative of anything on its own (unless there is a serious change!) – it is best to look at the trend over time for growth
- You can ask to see your child’s growth chart at appointments if you’re curious and don’t be afraid to ask questions if you have them, or bring up concerns
- Your family history of growth is relevant when it comes to your child’s growth patterns
- Growth is an indicator of health – so see your doctor if you have any concerns regarding your child’s health or nutrition!