Diseases & Conditions
Charts used by a pediatrician to compare a child’s measurements with those of other children the same age. It is important to be able to evaluate a child’s growth, tracking change over time and monitoring the development in relation to other children. Therefore, the growth charts used by pediatricians are a standard part of any well-child checkup.
There are two sets of standard growth charts for boys and girls—one for infants up to 36 months of age, and another for children aged two to 20 years. Boys and girls are plotted on different charts because their growth rates and patterns differ. The charts include a series of percentile curves that show the distribution of growth measurements of children from across the country.
The growth charts most commonly used in the United States were developed in 1977 by the National Center for Health Statistics; these were recently updated to reﬂect better cultural and racial diversity. The original infant charts were based on data from one study of middle-class, formula-fed Caucasian infants from southwestern Ohio. Because almost all the children studied were white, middle class, and formula-fed, the charts fail to reﬂect several differences in growth among different children. For example, healthy breast-fed babies tend to gain weight more slowly than their formula-fed counterparts. Asian children are often smaller than Caucasian children. As a result, a pediatrician may mistakenly conclude that a particular child is not growing or gaining weight adequately. Equally problematic is the fact that two different groups of children were used for the overlapping charts covering children from birth to 36 months and from two years to 18 years.
This meant that the same 24- to 36-month-old child can measure in a different percentile when progressing from one chart to the next, often leading to misdiagnoses and expensive clinical tests. Finally, the charts developed to compare weight for stature ended at 10 for girls and 11 for boys, making it difﬁcult to follow the growth of teenagers.
To correct these problems, several nutritionists, pediatricians, and statisticians at the National Center for Health Statistics, the National Institutes of Health, and the Centers for Disease Control and Prevention compiled a large sampling of new data from several recent annual national health and nutrition surveys based on millions of children. Their comprehensive data, covering children from birth to 20, better reﬂect the country’s racial and ethnic diversity and include formula-fed and breast-fed babies. The new charts are signiﬁcantly more accurate for monitoring the growth of infants, children, and adolescents.
The most important feature of the new growth charts is the inclusion of a measure called body mass index (BMI), which is calculated by dividing the weight by the height squared. BMI is commonly used to determine if adults are overweight and correlates well with a person’s total body fat. Nutrition experts have long advocated that BMI be applied to children and teenagers because a majority of overweight adults start as overweight children. The researchers found that by the age of eight it is possible to predict with great precision which child is likely to be overweight later in life.
At each well-child visit, the doctor records certain measurements in the child’s medical record. For an older child, for example, a doctor may plot height for age, weight for age, weight for height, and body mass index (BMI). An infant usually is measured for length, weight, weight for length, and head circumference for age. Weight for height (or length) compares someone’s weight at his height to other children’s weight at that same height (or length). Although weight for height charts can be useful for assessing body weight in children two years and older, the Centers for Disease Control and Prevention have stressed that the recently released body mass index charts are preferred for this purpose.
Head circumference measures the distance around an infant’s head at the widest point. Doctors take these measurements for premature infants, too. They correct for prematurity on the growth charts until age two years by subtracting the missed months of gestational time from the child’s chronological age—so an eight-month-old baby who was born two months early will be plotted as a six-month-old. Known as “corrected age,” this reflects the fact that a premature eight-month-old has been growing for two fewer months than an eight-month-old who was born on time. (By the time they are two years old, premature kids usually catch up to other children in growth.)
A growth chart has seven curves, each representing a different percentile: 5th, 10th, 25th, 50th, 75th, 90th, and 95th. The 50th percentile line represents the average value for age. There are also charts that show 3rd, 10th, 25th, 50th, 75th, 90th, and 97th percentiles. Doctors sometimes use these when they plot measurements that fall to the very outer edges of one or more growth curves. A child’s growth measurements will be plotted among these percentile curves.
Parents should not assume that a high or low reading means that there is a problem. A baby whose head circumference is in the 90th percentile might also fall in the 90th percentile for weight and length. The child whose weight falls in the 10th percentile may have parents who are a bit below average for height and weight; therefore, for this child, being in the 20th percentile is an entirely normal reading. Sometimes, however, a child’s measurement increases or falls sharply, or is at one extreme of the growth chart. For example, children who fall below the 5th percentile on the weight for height chart are considered underweight; children at or above the 85th percentile on this chart are considered overweight (and at risk for obesity); and those at or above the 95th percentile are considered to be obese. Generally, if a measurement exceeds the 95th percentile or crosses two percentile curves (such as climbing from the 40th percentile to the 75th percentile, thereby crossing the 50th and 75th percentile curves), there may be some cause for concern. On the other hand, if a measurement falls below the 5th percentile or crosses two percentile curves (dropping from the 50th to the 20th percentile, for instance), the doctor will also consider the possibility of a health problem. The growth chart should be viewed as a trend, not a fixed impression. What is more important is the examination of a growth chart reading over time to reveal a pattern of development. That pattern reveals how a child is growing in relation to other children.