Interpreting infant growth charts

Remember your first visit with your baby’s pediatrician?

I remember that it seemed like a HUGE deal just to leave the house.  Did we fasten BabyC in the car seat correctly?  Where can we sit in this waiting room where there will be 0% chance of a sick kid coughing on her?  OMG, she’s crying!  How long will we have to wait?  Should I feed her?  Yes, let’s try that.  (First time nursing in public.)  Five minutes later, when I had finally situated the baby and arranged the nursing cover and gotten a proper latch, the nurse called us back to the examining room… That’s what I remember.

Oh, but our visit with the pediatrician – what do I remember about that?  Two things.  First, he told me that, even though it seemed like my baby was nursing for 45 minutes out of every hour of the day, my milk may not come in for another 2 or 3 or 4 days.  And my baby might get a little hungry.  Great.  Second, the nurse weighed our baby and measured her length and head circumference.  Then we got those all-important percentile stats that told us how our baby compared to her peers.  So began a lifetime of pretending not to care how our baby measured up.

BabyC was born 8 lb. 9 oz. and 22 inches long: a big baby.  This came as a surprise, as neither my husband or I are very big people, and several OB’s had estimated that I was carrying a 6-7 lb. baby.  As our pediatrician looked over the neonatal notes from the hospital and BabyC’s measurements from his office, he commented that she was LGA – Large for Gestational Age. She was in the 95th percentile for weight and 100th for length.

I was not happy to hear my baby called LGA.  I had just devoted the last two years of my life to researching the effects of gestational diabetes on the fetus.  One of the outcomes of diabetic pregnancies is LGA babies, so I’d spent a lot of time reading about the adverse outcomes we see in LGA babies – both at birth and decades later.  I had to remind myself that by definition, 5% of all babies will be LGA, and most of these babies will grow up to be perfectly healthy.  I had eaten well and exercised plenty during my pregnancy, and luckily I was not diabetic.  So I told myself not to worry.

Within a few months, however, I found something else to worry about.  At her 4 month checkup, breast-fed BabyC was coming in at around 25th percentile for weight, and her height was dropping off as well.  Our pediatrician was a fairly laid-back kind of guy and told us not to worry.  He dropped the hint that we might consider trying some solids soonish, but he didn’t make me feel like my milk production was inadequate.  BabyC seemed like she was satisfied at the end of a nursing session, so I felt pretty sure that this was just her normal growth trajectory.

This got me wondering though – where do these growth charts come from?  Who are these babies with beautiful smooth growth trajectories?  This question also came up in the discussion around my last post (New Study:  Exclusive Breastfeeding Can Support Infant Growth to 6 Months of Age).  In order to conclude that babies grow normally in any experiment, researchers have to compare them to some standards for growth.  What is normal growth in an infant?

In the US, there are two sets of infant growth charts in use by pediatricians: one produced by the Centers for Disease Control (CDC) and one produced by the World Health Organization (WHO).  Both sets of charts can be downloaded from the CDC’s website.  Let’s compare the two:

CDC Growth Curves for children <24 months:

  • Released in 2000.
  • Include data collected from the National Health and Nutrition Examination Survey (NHANES) in 1971-1974, 1976-1980, 1988-1994, plus national vital statistics (birth weights), Missouri and Wisconsin vital statistics (birth lengths – only states where this is recorded on birth certificates), and the Pediatric Nutrition Surveillance System (lengths for 0.1 to <5 months).
  • Cross-sectional data, meaning a bunch of kids of different ages were measured and plotted by age.
  • Sample size for 2-23 months = 4,697 children for a total of 4,697 measurements.
  • Excluded babies born with very low birth weight (<3 lb, 4 oz).
  • Estimated 50% ever breastfed, 33% still breastfeeding at 3 months (not necessarily exclusively).  No information beyond that.

The WHO curves for children <24 months:

  • Released in 2006, published as this study¹.
  • Data were collected between 1997 and 2003 from children in Pelotas, Brazil; Accra, Ghana; Delhi, India; Oslow, Norway; Muscat, Oman; and Davis, CA, USA.
  • Longitudinal data, meaning the same kids were tracked at multiple time points, in this case at birth; 1, 2, 4, 6, and 8 weeks; and 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 16, 18, 20, 22, and 24 months.
  • Sample size:  882 children with a total of 18,973 measurements.
  • Excluded babies if they met any of the following criteria:
    • Low socioeconomic status; birth at high altitude; birth at <37 wks or >42 wks; multiple birth; perinatal illness; any condition known to affect growth; mom smoked during pregnancy or lactation; breastfeeding for <12 months; introduction of solid foods before 4 months or after 6 months; weight to length ratios >3 standard deviations above or below study median (i.e. babies that were super chubby or super lean were excluded so as not to skew the data).
  • 100% of babies were predominantly breastfed at 4 months, and 100% were still breastfeeding at 12 months.  Solids were introduced at a mean age of 5.4 months.

In September 2010, the CDC released a report² comparing the two sets of growth curves and making the recommendation that pediatricians use the WHO curves to assess growth of babies 0-24 months old, while continuing to use the CDC data for older children.  The CDC cited the following reasons why the WHO curves are better than their own data:

  1. The WHO data were specifically collected to define optimal growth.  They excluded children that were affected by any circumstance known to potentially inhibit optimal growth.  The CDC data included all children except those born very small – they represent average rather than optimal growth.
  2. The WHO growth curves include more data points, measuring 882 infants per time point.  The CDC data have only 72 weight measurements at 2 months (38 boys and 34 girls) and then 200 measurements per month up to 5 years of age.
  3. The WHO data only include children that were breastfed according to the current American Academy of Pediatrics (AAP) recommendations, while the CDC data include a cross-section of American children from the 1970s-1990s, the majority of which were fed at least some formula.  Why does this matter?
    1. More babies are breastfed now than when the CDC data were collected.  In a 2007 CDC survey, 75% of infants had ever been breastfed and 58% were breastfed for at least 3 months.
    2. Infant formulas have changed in the last 30 years.  They look a lot more like human milk in nutrient composition than they did when the CDC data were collected.
    3. Breastfed babies are known to grow differently than formula-fed babies.  Breastfed babies usually gain weight more quickly than formula-fed babies for the first few months of life, but beginning around 3 months of age, they gain slower than formula-fed babies.  This means that the CDC growth charts over-diagnose failure to thrive, resulting in expensive medical workups.  Use of the CDC charts for breastfed babies may lead to the misconception that they are not receiving adequate nutrition if they are “falling off” the growth curve, triggering advice such as starting solid foods earlier or supplementing with formula (which would likely decrease breast milk production).  Even if the doctor is aware of the differences in growth between breast- and formula-fed babies and tries to explain this to parents, it can be demoralizing to see your baby fall off the growth chart and cause unnecessary anxiety in a new parent.  (I can attest to that.)

The differences in the CDC and WHO data are illustrated in the figures below, taken from the 2010 CDC report.

Comparison of the WHO and CDC growth charts for girls <24 months.

Comparison of the WHO and CDC growth charts for length for girls < 5 years. Note that the WHO girls are actually taller (while also being leaner) than the CDC girls.

In November 2010, an article in the AAP News Magazine³ stated that the AAP supported the shift to the WHO growth curves for kids under 2.  However, making this change in pediatric practices may take some time, as it will require education, training, and probably some new software.

I was happy to learn that our pediatrician has already made the switch to the WHO growth charts.  As for BabyC, her 10 month stats would put her weight at 10% on the CDC chart and 20% on the WHO chart. Her length is at 5% on the CDC chart and between 2-5% on the WHO chart.  It turns out she’s just a little kid.  Knowing that she is a hearty, healthy eater now, I’m not worried.  In fact, I’m pretty sure she just went through a growth spurt, because all of a sudden she seems HUGE!

Did your baby’s growth percentiles change in the first year or two of life?  If so, were you worried?  Was your child’s pediatrician worried?  Do you know if your child’s pediatrician uses the WHO or CDC growth charts?

References:

  1. WHO Multicentre Growth Reference Study Group.  WHO Child Growth Standards based on length/height, weight and age.  Acta Paediatr Suppl. 2006 Apr;450:76-85.
  2. Centers of Disease Control and Prevention.  Use of the World Health Organization and CDC Growth Charts for Children Aged 0-59 Months in the United States.  MMWR 2010; 59(No. RR-9).
  3. Greer F.R. and Bhatia J.J.S.  CDC: Use WHO Growth Charts for Children Under 2. AAP News 2010; 31:1; doi:10.1542/aapnews.20103111-1.
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29 thoughts on “Interpreting infant growth charts

  1. Enoch was 10% in weight at 12 mo check up, the doctor told us to watch him so he doesn’t keep falling off the chart. That was a shock to me, because I still remembered that he was a fat fat baby at over 90% in weight just a few months ago when I was still breastfeeding. I almost feel guilty for weaning him. Now I’m wondering if the doctor was using the CDC chart. Thanks for the post!

    • Glad you found it useful! Looking at those pretty growth curves, it is hard to remember that all babies are different and might not have a smooth growth trajectory. It sounds like Enoch is doing fine now. Thanks for reading!

  2. This is awesome. Seriously, I searched for this kind of data when O was first born. I gave up trying because no one had a good summary like this and I was too exhausted to look it all up at the source! “So began a lifetime of pretending not to care how our baby measured up.” So true.

  3. Hello, thanks so much for your article. In my home, my babies are falling off the charts on the other end. And that chart haunted my days and especially my nights, which is when my babies do all their eating. I was super worried with my daughter. She was exclusively breastfed and throughout her first year she was in 90th percentile. At our second baby wellness visit, the doctor asked how often I fed her. When I told the doctor that I fed on demand, which was about every 1.5 to 2 hours, she asked in a very condescending tone, “Have you heard of childhood obesity?” I was shocked, scared, and clueless. I thought I was doing all the right things and I was mortified that my daughter was at risk for obesity. The doctor told me to feed her less. I was a first-time mommy and I felt so guilty. I was making my baby fat! But I could never do it. When she cried, I fed her. She was hungry. Can you imagine someone withholding food from you? In July, she turned two and at her check up she came in at the 50th percentile. Completely average. I also now have a 4 month old and he is a BIG boy (at least according to the chart, he’s perfect for himself). I feed on demand, but this time around I’m trusting my maternal instinct. If he’s hungry, he’s eating. He’s in the 98th percentile. I know I am very fortunate to be on this end of the chart. But really it’s just a chart and another label for moms to fret over. What is more meaningful? That chart? Or happy, thriving, healthy children? As for doctors, it’s really disappointing that the people we trust to our healthcare know very little about breastfeeding and the benefits. Thanks again for the valuable information, one that MANY moms will find useful. There will be a lot of relieved moms out there.

    • Hi Teli,
      Thanks for telling your story. I’d like to do more reading on correlations between infant birth weights and growth rates with obesity later in childhood or adulthood. Regardless of what the data say, asking a breastfeeding mom to withhold food from her hungry baby is just not practical. And the last thing you need is to feel guilty about feeding your child. I suppose the tricky thing about breastfeeding is that a baby might not suck just for nutrition but also for comfort. Anyway, I’m glad you did what you felt was right. I think the charts should serve as guidance and alert us if babies are really showing an abnormality in growth, but we have to recognize that babies will grow in spurts and that their growth rate/pattern is affected not just by nutrition and health but also genetics. And for doctors, I think there is a generational issue there. That said, we have had two pediatricians, one who has been practicing for ~30 years and one for ~10. Both have been very supportive and knowledgeable about breastfeeding, and I am thankful for that.

  4. My daughter, who was exclusively breast fed until I went back to work and then supplemented with formula) fell off the charts as well. She was ‘big’ when she was born (15 days after her due date), and was big for the first several months. Over time she fell lower and lower on the charts- and my the time she was mobile, she was in the 5th percentile.

    She’s have checkups where she’d grow several inches but only put on a few ounces.

    Thankfully we had level-headed docs that saw a healthy kid- and never got any pressure one way or the other.

    Given that I am obese, I pray that she stays slim her whole life. Now that she’s a toddler, we’re facing food battles when she doesn’t want to eat what is for dinner, etc. I struggle. I don’t want to force or cajole her into eating when she isn’t hungry/doesn’t want to. I also don’t want to indulge a toddler’s every whim.

    Now, I’m not worried about her being too small, I worry about influencing her eating habits so she’s grow up and be too big.

    • Hi Momma – Thanks for your comment. We always find something to worry about, don’t we?! I’m not looking forward to having a picky eater for a toddler, but I know that is very common. Your awareness of the potential for unhealthy food attitudes and habits to begin around this age is key. I think it is really hard to not pressure a kid to eat a little more when they are just picking at their food. Keep offering healthy choices and let your daughter decide when she is done with a meal. I’ve also read that offering many small, healthy meals/snacks throughout the day can help at this stage. All of this is probably harder in practice than in theory though. Good luck!

  5. Nice new blog, and thanks for the info on the growth charts. Jake hasn’t fallen off, but he was below where he had been (from ~70% to ~20% between his 6 and 9 month visits, coinciding with when he started eating finger foods). I’ve been wondering what he was being compared to, but didn’t have to time to look it up. This is very helpful for when we he gets his weight checked in the next couple of weeks!

  6. Thanks for such a great post! I have been searching for technical/evidence based info on growth charts and your post did answer a few of my confusions and doubts. I have a couple of questions here and i really hope you can shed some light.
    1. My baby A is of an Asian origin, does it mean using WHO chart will be more accurate since the data was collected from a highly diverse demographic that representing the world population compare to CDC, that samples were from The States?
    2. Can you share any site(s) that utilize the WHO growth chart and CDC chart?

    • Hi Shirley – glad you found this info useful! As far as your first question – yes, I would say that the WHO chart would be more accurate since it includes babies from 6 different countries. The CDC data comes from an outdated snapshot of the US population – so it would be as diverse as the population was at that time. I’m not sure what you mean in your second question. Are you looking for websites? You can download both charts from the CDC’s site (and print them out and plot your baby on them to see how they compare!) – http://www.cdc.gov/growthcharts/Default.htm

  7. Thanks again! My mind was running faster than my fingers, sorry that I did not place a complete question for #2. Yes, I was looking for websites that are utilizing WHO/CDC charts, those that make it into growth percentile calculator whereby we give our measurements and they pop out the percentiles. I just found a handful but most do not share the source on the calculator page itself until one flips forward a few pages. Initially, I thought using one of calculators will be a breeze, and I assume everyone use the most recommended source (from WHO) but I am wrong! All calculators that I came across are run based on CDC charts. So, the best is still back to basic. I am now reading my Baby A percentiles from the growth tables provided by WHO, hope I am doing the right thing for the sake of science :) I wish to hear from you if otherwise. Have a great weekend!

    • Oh, I get it:) Great question. I didn’t find any web-based calculators using the WHO charts either, but I didn’t do a thorough check. Please share it here if you find one. I’m not surprised that sites are still using the CDC charts. As far as I can tell, the AAP hasn’t made the switch yet, citing the need to educate physicians and nurses, and I suspect a big part of that is updating software to make it easy to use the WHO charts. Yup, sometimes doing it the old-fashioned way (pencil and paper) is best!

  8. Thank you Alice. This is the best plain English summary I have found explaining the strengths and limitations of standardised infant growth charts.
    I am a midwife and have thought about babe’s weights at birth, breastfeeding.. or not.. and how babies grow quite a bit. I believe that there is also an element of a healthy placenta will grow a healthy sized baby.. after that the child will grow into into its genetically predertermined size and shape… your baby C is a perfect example. Healthy mother who eats well providing great nutrition for her babe in pregnancy. Babe is a fabulously robust child at birth.. plenty of brown fat and fluid to keep her going until lactation is established.. then she settles down into the body (weight, height) she is genetically structured for – like her parents. Great antenatal care makes a difference too.

  9. I found the particular post very interesting since it is exactly what we are going through at the moment. My son was labeled “failure to thrive” at 10 months even though he is a very good eater and always has been. I think our doc uses the CDC chart, but I haven’t asked. I only came to this conclusion after doing my own research. My son was born small (4lb 13oz) but has always been long. I was the same way when I was a baby. It makes me angry that my son has been labelled this when he is clearly thriving! I’ve also read that growth can slow and sometimes dip while sleep training, which was happening right at the time we had his doc apt. Are the doctors these days taking on so many patients that they don’t have adequate time to spend getting all the data and facts about their patients? I like our doctor, but this has me seriously questioning whether to start “interviewing” other doctors. We have an apt with a nutritionist next week. It’s better than the endocrinologist they also wanted me to take our son to see. I am hopeful that it will be a positive experience. Why does everyone think that a small baby isn’t as healthy?

    Thanks for your post!

  10. Great summary!

    I use the Rourke growth chart (http://rourkebabyrecord.ca/growth.asp) which is based on WHO. My daughter was 99th percentile for both height and weight from about 2 months of age. She lost a bit of weight in the first few weeks of life because I wasn’t producing enough milk, so once she was switched to formula her weight gain took off. She is now 3.5 years old and is still in the 99th percentiles. Most people think she’s 5 years old. At our recent paediatrician visit, there was no concern about obesity, primarily because she is proportional.

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  12. Your blog is great! I am also a scientist/mom who happens to be very petite and thus have had petite children. So, this post was very interesting to me. My first little boy was breastfed from birth, but because of a tongue-tie never quite got the latch right and I had to give up at 2.5 months. He went up to the 9th centile once on formula and stayed there until he became mobile at 6.5 months. He then dropped to the 3rd centile and has continued to drop down the growth curve. At nearly 3, he now weighs only 23 pounds (0.45th centile) and 36 inches for height (I think 25th centile). My 6 month old son started out strong in the 32nd centile for weight. I was successful in breastfeeding him and though I read everything on the optimal amount of time to nurse on each side, how to increase milk production etc., he has continued to drop down the growth curve as well. He is now just about 15 pounds (2-3 centile?) and I had such increased anxiety that I wasn’t making enough milk. Our pediatrician advised us to start solids around 4-5 months and we have done so, without gaining much ground. He is now crawling and burning more energy than ever (just like his brother), so I feel like I worry even more about making sure he’s getting enough. And you’re right – it is just demoralizing to see your child’s growth rate drop. But some of that is just what’s in the genes! I was eager to compare my children’s growth with mine and my husband’s baby charts. I scavenged the internet for a program that would allow me to keep track of this online, but was unable to find anything like that. Most sites just let you calculate a percentile, but it’s hard to figure out where the data is coming from for their curves. I ended up reconstructing my own curves in Excel with the CDC spreadsheets. I was encouraged to see similarities in all of our growth curves (in spite of gender and feeding differences).

    Thanks so much for writing about this subject. It’s important to not make judgments about this until you know what data you’re comparing your kid’s growth to!

    • Hi! Thanks for telling your story. I agree – it is definitely important to look at our kids’ genetics when it comes to growth. The growth curves don’t consider that aspect. I think it is a great idea to reconstruct your own growth curves and see how your kids compare! That gives you a huge amount of information and should provide some reassurance. Thanks for stopping by, and I hope you keep reading the blog! I love discussion with smart moms:)

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  14. Thanks for this info! I hadn’t realized there was a difference. I remember when my daughter was first born the chart DID intimidate me a lot. My little girl was born a healthy weight- 6lb, 9oz, and continued to gain weight throughout her first year, but she didn’t get on the growth charts until after her first birthday. She never exhibited other symptoms that would give cause for concern other than her size. Developmentally she was either right on time or advanced- especially with the cognitive/ linguistic stuff. (I nursed her exclusively until she was introduced to solids around 6 months, and then continued to nurse her supplementally until she was about 18 months.) I think that for the outlier babies- both large and small who are barely on or aren’t able to stay on the graph- there can be a lot of anxiety for the moms; however, experience can often alleviate that tension because size alone is not a negative omen for health. Recognizing that my daughter WAS thriving in the other areas, and still steadily growing in physical size despite not keeping pace with the average for her age and sex was probably the most helpful thing for me in overcoming that initial growth chart panic.

  15. I have a similar question to Nica. I’m not sure if you are monitoring comments on this post anymore, but my son is 4 months and has always been around the 50th percentile for height and weight. I am surprised by this because my husband, daughter, and I are all quite tall (not sure our percentiles, but husband is around 6′, I’m 5’10″ and daughter is 95th percentile). Do you know if my son will always be the short one in the family or might his height take off when he’s a little older? I’m not really concerned for any health reason, just think that he might not like being the shorty… :)

  16. Yes! My daughter was born 10 lbs 2 oz and 19 and a half inches. She was in the 100th percentile. I did not have gestational diabetes. I had a normal pregnancy, although I have hypothyroid and PCOS. My biggest issue while pregnant was high amounts of water retention (I looked due at about 6 months, and looked like I was having triplets by month 8). I also put on 66 lbs despite eating healthily. About 30 lbs were water. It came off without breastfeeding within two weeks.

    While born at the 100th percentile, at less than 20 lbs at 10 months today, she has not doubled her weight. The doctor said she was a little above the 50th percentile. That may not seem to be bad but I feel as if it’s a drastic change from birth. However she is lean, very active, and hit every milestone early. She’s been crawling since 6 months, sitting up unassisted since 4 months, and just started standing unassisted at 8.5 months.

    Some babies have their own wacky curve that does not follow any curve represented by charts. All babies are different.

  17. My son was born at 8lb5oz about in the middle, but he has dropped off the bottom of the curve. His height:weight ratio / BMI is almost a perfect 50% but much smaller than normal, even way below the 97% charts. He is 19 months and looks like a 10-12month old.

    For a while (upon our pediatrician’s insistance) we tried feeding him more and more, and he just got really fat. Just rolls of fat with sores in his skin folds, and didn’t get any taller, so we went back to a normal healthy diet where he looks good.

    He is perfectly healthy otherwise, learning words very quickly now and has a lot of energy, he laps around the house all day long.

    I guess some kids are just smaller. I was looking for 99% charts but from what I read they get very inaccurate beyond 95% and don’t really help you. Ultimately it’s just up to the parent and pediatricians to determine that the child is healthy.

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