Child Growth Charts: What Those Percentiles Really Mean

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Blame it on the human impulse for numbers and comparisons, but probably the highlight of any doctor's checkup for your child is to see where he stacks up on the growth chart and which percentile he's in for height and weight. "Parents just love growth charts and percentiles: at each visit they anxiously await the percentile and can be visibly disappointed if it's too low or high," acknowledges Sara Connolly, MD, a pediatrician and expert at Bundoo. Still, the intense elation or disappointment these charts bring parents can be misguided if they don't know how to interpret these numbers.

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"I always tell parents not to think of the growth chart as an exam: it is not better for a child to be 90th percentile than the 10th percentile," says Deena Blanchard, MD, a pediatrician at Premier Pediatrics NY. "All it means is if your child is, say, at the 50th percentile for weight, that means if you took 100 children that age and put them in a room, that child would weigh more than approximately half of them." From birth until age 2, there are three charts physicians follow: weight, length, and head circumference. After age 2, physicians follow weight, height, and body mass index (BMI). The percentile categories are generally broken down into 5%, 10%, 25%, 50%, 75%, 90%, and 95%.

But far more important than any one percentile reading is whether that percentile changes over time. "For example, if your 2-year-old is at the 50 percentile for height and weight just like he was at 6 months, a year, and 18 months, then I am pleased," says Dr. Connolly. "Consistency shows appropriate rates of growth in height, weight, and head circumference. If I look at your 2-year-old and he is at the 50th percentile for height but was at the 99 percentile for height before that point, I might worry. In this case, he would have crossed downward a significant amount. I would wonder if he was no longer growing well, if there was a nutritional or genetic issue."

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Yet even when a child jumps up or down a percentile category, that's not necessarily a reason to worry. "There are times in life when percentiles can change," says Dr. Blanchard. "For example, around 9 months of age, children will 'find their genetic curves' and may change percentiles. If the change is a one-time occurrence and the child starts to grow along the new curve, there is no cause for alarm. Children do not always follow the exact line of their curve and slight variations are nothing to worry about. But when a child crosses two percentiles either at one time or over frequent visits -- for example, goes from the 50th percentile to 25th percentile to 9th percentile -- then a physician will start to be concerned." 

These days, pediatricians say they usually see percentiles for weight increasing. "For example, a 1-year-old who was at the 50th percentile for weight is now a 3-year-old at the 99th percentile," says Dr. Connolly. "Everyone knows that obesity is a major problem in the United States, but many parents fail to recognize when their child is at risk. Growth charts and increasing percentiles help pediatricians gently call rapid weight gain to their attention."

Growth charts can also be tricky as they are representations of what an average kid looks like -- which does not mean optimal or ideal. "If your genetics are on the shorter side, then of course your child will be on the lower percentiles and vice versa," says Dr. Connolly.

Bottom line: "I encourage parents not to obsess over the growth chart," says Dr. Blanchard. "If a child is healthy and developing normally, it is unlikely that any major medical problem is occurring."

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