5 Things You Need To Know About Growth Charts

Do you find yourself wondering if your child is growing “normally”? Do you find yourself comparing your child’s height or weight with other children when you take her out to play in the park? Do you begin to make plans about how you will change her diet when your doctor informs you that she is below 50th percentile in weight for her age?

If so, you are not alone. It is a natural instinct for any parent to worry about the growth of their child. In my post on Take a Step on the MyPyramid for Preschoolers, I introduced you to how you could make a growth chart for your toddler based on his height and weight. In this post, I provide you more details and suggest a few actions for you to consider as you think about your child’s growth.

Growth charts are based on national population statistics

Data on physical measurements (weight, head circumference, length, standing height etc.) for children of different ages is collected from national surveys and analyzed using statistical methods to prepare the growth charts. These charts show lines for various percentiles, which are used as a reference for comparing the actual measurements. There are two limitations of this method that you should be aware of:

1. Just like the census, national health surveys are not done every year. In fact, the last National Health and Nutritional Examination Survey (NHANES III) was done during 1988 – 1994. This led to a revision of the 1977 growth charts in the year 2000. Amazing, isn’t it, that today’s growth charts are based on data that is 15 years old! Surely, a lot has changed since then.
2. Data is collected based on a “statistical sample”, which is supposed to represent the true nature of the whole population. Although there are some rules for estimating this “statistical sample”, no one can say with 100% confidence that it really represents everybody. In the interest of creating a “normal” growth profile, the researchers have to make some trade-offs and not include various special cases. It is important for you to be aware of what those special cases are. Your pediatrician should be able to advise you if you happen to be one of them.

Having said that, the current growth charts are still a very useful tool to evaluate the general growth pattern your child in relation  to what is normally expected. Recognize that the researchers do a very good job planning for a national survey to really “fill the gaps” in their current data and understanding. For example, in the NHANES III, they over-sampled infants and toddlers 2 months – 5 years old to properly account for the growth patterns in this age group. They also included a higher number of breastfed children to reflect the rising rates of breastfeeding compared to previous years. They utilized advanced statistical methods to create a better and smooth transition between infants/pre-schoolers and adolescents.

Growth charts are age and sex specific

Different measurements are made on infants (less than 36 months) and toddlers/adolescents (2 – 20 years). For infants, weight, head circumference and head-to-toe height is measured in a lying down position. The measured data is evaluated on these 4 types of growth charts:

1. Length for age
2. Weight for age
3. Head circumference for age
4. Weight for length

In most cases your pediatrician will show you the first two charts; usually blue for a boy and pink for a girl.

For toddlers/adolescents, weight and height is measured in a standing position. The measured data is evaluated on these 3 types of growth charts:

1. Weight for age
2. Stature (height) for age
3. BMI (Body Mass Index) for age

Again, your pediatrician will most likely show you the first two charts. However, the BMI for age is the most important chart in my opinion (see below)

Growth charts do not apply to preemies and other special cases

Data from very low birth weight (VLBW) is  not included in the infant growth charts since their growth patterns are known to be very different from higher weight, full-term infants. If this applies to you, there are other specialized growth rate charts you can ask your pediatrician about. The best general growth charts in this case are based on the the Infant Health and Development Program (IHDP) data, which can be used from 40 weeks to 36 months. It is not, however, without its limitations; so you should have a good discussion with your doctor.

Other special cases include health conditions such as Down syndrome, cerebral palsy and Turner syndrome. Special growth charts are available but again, they have many limitations.

Although, I did not find any discussion on the topic of multiples (twins, triplets etc.) I think that these too are special cases. Usually, multiples have low birth weight and do not go to full-term. Even though, the NHANES III data included low birth weight infants, I did not find any reference of categorizing data for multiples. Multiples may also show different growth patterns, where one of the child grows “normally” but the other(s) lag behind. It is my (selfish) hope that the next national survey will try to account for this gap.

Pay special attention to the BMI for age growth chart

Body Mass Index (BMI) is calculated using both weight and height. It is very easy, and you can use this online calculator simply by entering the age, weight and height. BMI is known to track very well with age, first increasing from birth to 8 months of age, then falling until age 6 and finally rising with age. There are two important things you can learn from the BMI chart with age for your child -

1. Percentile – Your child is at high risk of being overweight if the BMI is between 85th and 95th percentile for his age. If the BMI is over 95th percentile, then the child is considered overweight.
2. Trend in BMI for age chart – the sooner your child’s BMI hits its lowest number, the more likely he  is going to have a higher BMI percentile when he grows up, and greater is his risk of being overweight. Watch the trend in BMI for age over time closely and take action sooner than later.

BMI-for-age chart, Boys, >2 years old

Growth charts are used only as a screening tool

It is important to understand that growth charts are used only as a screening tool and not to diagnose a medical condition. The 5th percentile cut-off is useful to identify infants at risk of overall health and growth problems. The 95th percentile cut-off, especially on the BMI for age chart, is useful for early identification of childhood obesity. However, resist the instinct to be alarmed by a single point on these charts. You should look at a series of points over several visits to understand the overall pattern and assess if there is any unexpected change. If you have a concern, consider making these charts more frequently. With online tools, you don’t have to wait for your next doctor visit.

Take action

Here are 5 actions you can take:

1. Use information to manage your concerns and anxiety over what is a “normal” growth pattern for your child. Hopefully, this article is helpful; however there are a few more resources you can use to learn more about growth charts:
   • CDC’s growth chart website
   • Use and interpretation of growth charts – an instructional guide
   • Recommendations for growth references for VLBW infants
2. Resist the urge to make nutritional changes or goals based on a single data point on a growth chart.
3. If a single data point causes concern, track more often and then make a plan in consultation with your pediatrician.
4. Resist the urge to compare your child with others, or even with his own brothers/sisters. For example, two children with the same BMI could have very different risks based on their age.
5. Take a long term view to your child’s growth.

Feel free to share your personal experience and advice regarding growth charts.

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Tagged as: BMI, CDC, Childhood Obesity, Growth Chart, Healthy Growth, Height, overweight, VLBW infants, Weight