Growth Chart Confusion: You Mean the 95th Percentile Isn’t an ‘A’?

growthchartI recently read a statistic that I honestly don’t believe.  But if it’s even close, we doctors have some ‘splaining to do.

It’s estimated that up to half … HALF!! … of parents don’t know how to interpret the growth charts that pediatricians and family docs pull out at every well visit to record your child’s height and weight.  Believe me, this is not a reflection of parents’ brain power.  Healthcare professionals, we should be ashamed of ourselves!  First, we make the charts as complicated as a Russian novel, and then we fail to explain them.

Moms are pretty caught up in how our kids are growing.  From that very first baby visit we wait breathlessly to see how many ounces have been gained and inches added.  It goes to the very core of our mothering — are we good enough?  WOW! She gained 14 ounces?  That’s some powerful breast milk, huh?

Sometimes the in-between weeks seem too long to wait.  I remember weighing my daughter in one of those hanging scales (do they even have those anymore??) in the produce department one day when my curiosity got the better of me.  I’ll take 2 pounds of apples and 8 1/2 pounds of baby.

Then later come the pencil marks on the wall.  In our house the homemade chart was behind the door in older son’s bedroom.  He was definitely the alpha male of the sib group and set the standard that the others aspired to.  Mom and Dad’s pencil marks were there too — even the grandparents took their turn, but somehow those lines never moved.

Cheating was an issue.  We enforced a shoeless rule, but younger son was frequently caught trying to lift those heels off the ground just a smidge.   And it was never clear if we should count older’s curly hair, or flatten it.  They started putting little sister ( who was 5 years behind younger son) against the wall for her pencil marks before she could stand by herself.  One would hold her under the arms while the other straightened her legs, making absolutely sure that those tiny heels were touching the ground.

The fun was in the comparisons.  Who was taller at 3 years and 4 months?  Were they the same height at 7 1/2?  Now we all laugh, because while it seemed that older always had at least a half inch advantage over younger at any given age, fast forward ten years, and at full adult height younger son is taller by a good 4 inches.

But I digress.  Back to those charts.  They come in two colors, pink for girls and blue for boys.  This is because growth curves are different for girls and boys, and the curves represent a comparison between your child and all other children of that age and sex.

Your doc will plot your kiddo’s height and weight along the line for her age.  Where that ‘dot’ falls along the curve tells you how your child’s height and weight compare to her peers.

So if she’s 18 months old, and her height falls in the 75th percentile, it means that she’s taller than 75% of girls who are 18 months old.  If her weight is also near the 75th percentile, then she’s heavier than 75% of her playmates.   Slightly taller and heavier than average (the 50th percentile) and perfectly normal.

Chances are, that represents some combination of your size and Dad’s  — at least at that age.  What combination?  That’s a roll of the genetic dice.

Same for a child whose dot falls at the 20th percentile for height and the 10th for weight.  She’s petite and thin (heavier than just 10% of her peers), but as long as she’s following along that part of the curve — not falling way below it, or spiking either height or weight way above it — she’s just perfect.  Exactly as her genetics destined her to be.

Some kids will continue to follow along the same curve as they grow, others will settle on a different one.  That depends on several variables, including diet, health, and again, Mom and Dad’s growth history.

Let’s look at another scenario.  Say my little 3-year-old guy comes in at around the 95th percentile for height and slightly higher, approaching  the 100th for weight (there is no 100th – you can’t be heavier or taller than 100% of your peers).  I’m thinking that’s pretty good.  He’s taller than almost all his friends (I’m so proud), and sure he weighs more, but isn’t that because of his height?

Actually, we should take another look at this kiddo.  Children who are overweight (and this guy’s at the very top of the weight curve) also tend to be taller than their peers at earlier ages.  We’re not sure why, it could be that they secrete higher levels of growth hormone, but it’s a fact that at the high end weight and height often travel together.  So even though my guy’s height is up there, we still need to be concerned about his nutrition and overall health.  In this case, the 95th percentile isn’t necessarily an ‘A’.

Bottom line:  the chart lets you and your child’s doctor know that growth, which is one sign of overall health, is progressing normally.    The trend over time is more important than any one point.  If your guy is following along his own curve, whether it’s the 10th percentile or the 80th, all is A-OK in the growth department.  Traveling the very top or very bottom?  Falling off the curve? Let’s check it out.  There may be a health problem that’s affecting growth.

This is not a competition.  There are no grades.  Bigger isn’t better and no two kids are alike.  Each of us is different, and nutrition and health being equal, we all end up just the size our genetics meant us to be.

That wasn’t so hard to explain, was it?

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Rachel Zahn, MD is a pediatrician turned health writer who had three kids during medical school and pediatric training—crazy, huh?


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