At his previous checkup, Max's weight was in the 95th percentile, but his head measurement was in the 25th. Although the doctor said her son was healthy, the difference in Max's percentiles scared DeSilva. "I was measuring his head at home daily," she says. "I kept wondering if there was something I could do to improve his percentile."
DeSilva is not alone. When pediatricians report a child's percentile during her checkup, many parents don't understand what the number means. Often, they mistake percentiles for percentages. If a child is in a high percentile, they boast about it. If the percentile is low, parents worry that there may be something wrong with their child.
Dave Olson, chief of pediatrics at the Munson Medical Center in Traverse City, Michigan, frequently calms parents' worries about percentiles by explaining they are not grades, but a way of measuring a child's growth over time. "There is concern, usually undue, about these curves," he says, adding that healthy children can be in any percentile. "There is a broad range of what we consider normal."
During your child's visit to the doctor, you may have noticed your pediatrician referencing a set of pediatric growth charts. First compiled by the National Center for Health Statistics (NCHS) in 1977, these charts display a series of curves that illustrate the ideal growth rates of children based on national statistics.
Pediatricians reference these charts based on the age and sex of a child. When a child is in the 90th percentile for weight, it means that, out of 100 kids the same age and sex, only 10 are heavier, and 90 weigh less. There are separate charts for weight, height and head size, so a child is likely to have a different percentile for each category.
Surprisingly, a percentile in one year does not mean much to doctors. "A child in the 10th percentile for weight who is healthy and developing well in all other respects is probably normal," says Dr Olson.
Percentiles are not static. A child's percentile may rise or drop between annual checkups. "During the first two years, a child's growth rate varies," says Moshe Adler, MD, a pediatrician at Pediatric Associates in West Palm Beach, Florida. "They may bounce around on the growth chart." Dr Adler mentions that older children may have varied percentiles, too. "If a child has been ill for a significant period or has a chronic illness, he may not grow as well as other children."
Instead, an excessive rises or drops or erratic fluctuations in percentiles signal a problem to health professionals. "The concern is with children who are healthy, eating well and have no known illnesses, but are not growing at a normal rate," says Dr Adler.
If a child's percentile is an issue, pediatricians may run a variety of tests to determine the problem. "What we do depends a lot on what the child's growth has been over a period of time," Dr Adler says. "If an otherwise healthy child is not growing, then testing may be necessary to determine the cause of the growth delay."
Testing can be harrowing for kids. When Jackie Fishman took her son to his one-year checkup, she was told he was in the 5th percentile for height. "We were reassured that, although he was small, he was normal," she says.
At the time, the pediatrician estimated that Fishman's son would have an adult height of 5 feet 5 inches to 5 feet 6 inches. As the boy grew older, however, that prediction changed. "Around age 10, he actually fell off the growth chart," Fishman says of her son. "When he was about 11, I had him tested for sufficient growth hormone."
Fishman's son underwent blood tests and a series of hormone stimulation tests. Sometimes, these can be uncomfortable, especially for kids. Although the initial tests showed that his levels were normal, the experience was too much for Fishman's son. She declined to have him go through more invasive testing.
"Sometimes I regret that decision," Fishman says. "Perhaps, if I had paid more attention to the time that his growth first slipped off the percentile chart, I might have been able to get him some treatment and help him gain a couple of extra inches." Nonetheless, today, Fishman's son is 5 feet 2 inches tall and in all regards, a normal, healthy teenager.
Dr Adler says that, when pediatricians prescribe growth hormone, parents can be assured that the child's percentile will improve. "The drawback is that growth hormone treatment can be very expensive and time consuming," he says. "Injections need to occur several times a week over a period of years."
Fishman's advice for parents is not to worry about percentiles. "Percentiles are approximations," she says. "They don't necessarily forecast the future growth of your child in a failsafe way."
Dr Olson agrees. While the curves on the chart may be smooth, few children's growth rates follow a perfect arc. "Parents have to remember that the 'normal range' is a statistical concept," he says. "Normal kids can be outside the normal range." Parents should be concerned if their child's growth remains below or above this range. "Significant deviations outside this range bear at least thought and perhaps exploration," he says.
In the case of DeSilva's son, Dr Olson says, Max's head size is normal. If the percentile were larger, he explains, then DeSilva should worry. "If an infant's head size begins to steadily move up from the 25th to 50th to 95th percentile, it is possible that the head is growing too fast due to a problem, such as hydrocephalus," he says.
"One thing to always keep in mind is genetics," Dr Olson continues. "Generally, if I find a child has a large head and it may represent a problem, the first thing I do is measure the parents' head circumferences and plot them on standard adult curves. Usually one or both have large, normal heads, and this is the explanation for it."
The pediatric growth charts continue to develop as researchers make new discoveries in nutrition and growth. In April 2000, the NCHS released new growth charts that reflected the measurements of American children more accurately and included assessment tools for body mass index (BMI). Doctors use BMI to assess body fat and track weight problems and obesity. "This is useful information to follow, because kids are at greater statistical risk for disease if their BMIs are high," says Dr Olson.
While percentiles are one of the best ways to track growth, they were never meant to be used as the only diagnostic instrument. Dr Adler suggests that pediatricians take care in tracking growth. "You really have to look carefully at the growth chart, and the child's age and history, too."
Dr Olson also stresses that each child is unique and will grow at her own rate. "There are specialized curves that plot kids from different countries and those who have medical conditions," he says. "Remember, you always have to compare apples to other apples."
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