Growth charts and curves in children – what you need to know
I am really ambivalent when it comes to growth charts and curves.
On the one hand, they can be a very basic and important tool and if used wisely, they are helpful in the detection of the early signs of a wide range of pediatric conditions.
On the other hand, I feel that the use of growth charts has somehow turned into the main topic of discussion at regular doctor visits or between parents. And so, instead of leaving the visit having received important advice that can be helpful with maintaining the child’s health and well-being, the mother leaves the visit recalling completely unnecessary information such as “the nurse said my child’s weight has decreased from the 57th to the 43rd percentile”. What does this even mean?
If that’s all there is to it, it really means nothing.
This post has two main goals:
1. To explain what growth charts are and what percentiles represent.
2. To try and give parents the tools to understand when an increase or decrease in growth percentiles is important and when it is negligible.
Growth charts and curves – what are they?
The formal definition is the following:
Growth charts are graphs that are used by professionals and parents in the first few years of growth in children. They represent one of the more important methods for assessment of the general health and nutritional state of the child.
Growth charts describe the weight, height, body mass and head circumference trends in children and teenagers according to age and sex, with the help of percentiles. Each country has its own set of national growth charts. I suggest you look for your country’s growth charts online. You can find the CDC growth charts here, these apply to children worldwide.
What is the role of growth charts and percentiles?
The easiest way to answer this is by giving an example.
Bob Smith was born at term, at 39 weeks’ gestation, with a birth weight of 2850 grams. At the age of 3 months, he weighs 4450 grams. Is this normal? Do these number make sense? How do we decide?
It is of course possible to recall from memory that the desired rate of weight gain in the first 3 months of life is 750 grams per month (look here for more frequent questions about infant feeding and nutrition). So just by looking at these numbers we can now tell that this baby hasn’t been gaining enough weight. But it’s not very practical to remember such rules for different ages, weights, heights, head circumferences and genders. Therefore, growth charts and percentiles are used.
If we open up the link that leads to the growth chart that depicts weight for age percentiles in boys from birth to 24 months (link here) and insert Bob’s current weight as well as his birth weight on the chart, we will find that:
– At birth his weight was in the 10th percentile
– His current weight is under the 3rd percentile.
And this is how we realize that Bob’s weight gain has been insufficient; his weight dropped from around the 15th percentile at birth to under the 3rd percentile at 3 months.
Would I have been equally concerned regarding a baby whose weight had dropped from the 85th percentile to the 70th? Not necessarily, and that is my exact point. More about this below.
What do these percentiles even mean?
The 15th percentile means that 85% of the children in the world weigh more than Bob Smith, and 15% weigh less. In most computerized systems you are able to get the exact percentile number when you insert a child’s weight.
This same percentile growth charts exist for length and head circumference. Of course, there are different charts depending on age and gender.
What about special populations? Nowadays, it is becoming more common to find different growth charts for specific populations, because it is obvious to everyone that the rate of growth of a child born prematurely, at 29 weeks’ gestation is different to that of a full term born at 39 weeks. There are different growth charts for children with chronic diseases, those born prematurely, those with Down’s syndrome, etc. So, before placing a child’s data on charts, make sure the child is healthy and doesn’t need to be compared to his “own” unique charts.
What is the problem that rises with the use of growth charts?
a. Not all babies follow the same, identical growth curve and they cannot all be compared to a single world-wide or national growth chart. One child’s parents can be basketball players, the other – football players. One child may have breastfed until the age of one year and did not receive any formula and the other could be inhaling 210 ml of formula every 3 hours. How can one compare all these different kids to a single curve?
b. Growth is dynamic. Therefore, being excessively occupied with percentiles and completely ignoring thousands of other items of data while assessing children is wrong. A kid who is in the 5th percentile can be perfectly healthy and be reaching his full height potential or he may have a huge underlying growing problem that needs further workup and diagnosis. Therefore, a single absolute value is not very useful when looking at growth curves.
Of-course, giving data received from growth charts disproportionate attention may increase parental anxiety and lead to redundant workup, too.
Therefore, in my opinion, given all the advantages and disadvantages, growth charts and curves are an additional tool that a health professional has to help him assess the child’s health status. If used wisely, it can be useful in providing a reflection of the child’s health.
What do I place emphasis on when it comes to growth charts and percentiles?
a. A good health professional knows how to differentiate between a healthy child and an unhealthy child with the help of their clinical instincts and the information they collect. In a well-developed, healthy child, percentiles are not so important. In a child who is unhealthy, I would further look into his growth and put an emphasis on the whole percentile issue, as well. Additionally, most pediatricians have the normal rate of growth in terms of weight and head circumference memorized and are able to distinguish between normal growth and abnormal growth within minutes, without the need for percentiles.
b. One should be aware of a change of more than 2 percentiles between visits. The computerized system gives us an absolute value nowadays but using the traditional growth charts one can identify a drop or increase that exceeds 2 percentiles. Such changes require the professional to stop and think whether this is normal or abnormal. Here too, in most cases, there is nothing to be worried about.
c. Be aware of children whose data lie on the different extremes in the charts. Being in the middle is usually an advantage. Therefore, a child whose weight percentile has dropped from the 60 to 40 is usually less concerning than one whose weight dropped from the 20th percentile to the 3rd.
d. Monitor changes that occur over time. If you ask 3 different physicians to measure the head circumference of the same child at the same time you will usually get 3 different results, each of which will lie on different percentiles. A drop in the head circumference percentile from 40 to 30 over a period of two months, in a well-developed baby, may not mean anything but it is still important to ask the parents to return for follow up in one month. In such cases I would also write a note to myself to examine the child’s development and consider performing a head ultrasound during their next visit.
So, to summarize, try not to turn the growth chart discussion into the main conversation during the visit but also try to identify growth trends that match the child’s health and development.
When in doubt, see a pediatrician and allow them to decide whether your baby needs monitoring or further workup. Because at the end of the day, pediatrics is an art.