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Dr. Tiongson, I have a question about BMI
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nursingbug posted:
Hi! I was the one that posted about my 3 year old with the high bmi- it was 96%.
Can you tell me what a normal BMI is for a child this age? or is it still one of those percentille growth things, where you just want to make sure they are consistently in the same place?
Her doctor showed me her growth pattern on a chart, and even though she is always in the 90ish percentile, he said she had gained more than would even be expected for her.
Any additional information would be appreciated! thanks!
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Christopher Tiongson, MD responded:
Youare correct. It is a percentile-based measurement.

The pattern for a kid BMI is like a wave through childhood. Toddlers are natually a bit heavier relative to their height and have a bit less muscle mass relative to their weight.

As kids become preschoolers they start to slim down. As children approach puberty both the boys and girls start to add muscle mass (which is a healthy increase in BMI) and the girls start go through their body changes, the BMI goes up again. This change over time means that we have to follow percentiles to track whether the height and weight are a healthy match.

For example, 50%ile for a 2 yr old girl is a BMI of 16.4.
By age 3 the 50%ile drops to 15.8
And by age 15 it is 20. It's easier to follow on the graph.

Here's the BMI chart for girls
http://www.cdc.gov/growthcharts/data/set1clinical/cj41c024.pdf

Here it is for boys
http://www.cdc.gov/growthcharts/data/set1clinical/cj41c021.pdf

And to top it all off, BMI is not just a simple ratio of weight to height. It is actually weight per body surface area (which is related to height.) So while a 90%ile height and 90%ile weight would seem to be exactly proportional (i.e. 50%ile BMI) the numbers don't come out that way. It would be more like 85-90%ile BMI.
 
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Christopher Tiongson, MD replied to Christopher Tiongson, MD's response:
sorry, wrong link for the boys chart

here's the right one
http://www.cdc.gov/growthcharts/data/set1clinical/cj41c023.pdf
 
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normarae5 replied to Christopher Tiongson, MD's response:
This was really helpful...I was just reading different post and ran across this one. Thanks


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