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Doctors have long recognized the value of evaluating babies' and children's growth and comparing it with that of other kids in the same age group. By doing so, they can track a child's growth over time and monitor his development in relation to both other children and himself. The growth charts your pediatrician uses for this purpose are a standard part of any well-child checkup.
This article will help you become familiar with these charts. As you learn more about them, you will discover what an important tool they are.
What Are Growth Charts?
Doctors use growth charts to compare a child's measurements with those of other children his age. This helps the doctors determine whether a child's growth is adequate. Boys and girls are plotted on different charts because their growth rates and patterns differ. For both boys and girls there are two sets of standard charts: one for infants ages 0 to 36 months and another for children ages 2 to 18 years. The charts are 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 by the National Center for Health Statistics and were first released in 1977. Recently, the center revised the charts to update their data and reflect greater cultural and racial diversity. (The original infant charts were based on data from one study of mainly middle-class, formula-fed Caucasian infants from southwestern Ohio - not a very inclusive population sample. The data for the older children's charts were collected in national health surveys from 1963 to 1974). Also, these new charts go up to age 20.
Looking at the Charts
The new charts represent the most recently published (June 2000) standards for U.S. children. By plotting your child's measurements on these charts, doctors are able to compare your child's growth patterns with data collected on thousands of U.S. children. Remember that only those measurements that are obtained in your child's doctor's office or taken by another properly skilled person should be plotted. Home measurements are frequently inaccurate and can lead to faulty data.
The commonly used standard growth charts include:
For children ages birth to 36 months (3 years):
Girls' length and weight for age
Boys' length and weight for age
Girls' head circumference for age and weight for length
Boys' head circumference for age and weight for length
For children ages 2 to 20 years:
Girls' stature (height) and weight for age
Boys' stature (height) and weight for age
Girls' weight for stature (height)
Boys' weight for stature (height)
At the Doctor's Office
During regular well-child visits, your child's doctor will record certain measurements in your child's medical record. With an older child, a doctor may plot four numbers on the growth charts: height for age, weight for age, weight for height, and, a recent addition, body mass index (BMI). An infant usually is measured for length for age (because kids usually can't cooperate for an accurate standing-height measurement until about age 2 to 3 years), weight for age, weight for length, and head circumference for age.
Length or height for age is simply a child's height at that particular age. The same is true of weight 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 fatness in children 2 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. Body mass index is calculated from both weight and height and in most cases is a fairly good indicator of a child's amount of body fat. 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 2 years by subtracting the missed months of gestational time from the child's chronological age - so an 8-month-old baby who was born two months early will be plotted as a 6-month-old. That reflects the fact that a premature 8-month-old has been growing for two fewer months than an 8-month-old who was born on time. (By the time they are 2 years old, premature kids usually catch up to other children in growth).
What Do the Percentiles Mean?
When you look at a growth chart, you will see seven curves that follow the same pattern. Each one represents 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). Your child's growth measurements will be plotted among these percentile curves. To better understand how to interpret those readings, consider these examples.
An infant whose head circumference falls in the 90th percentile will be plotted right on the second curve from the top of the chart (the 90th percentile curve). Being in the 90th percentile means the child's head measurement is greater than or equal to the measurements of 90% of children that age in the country. The remaining 10% of infants that age have head measurements that exceed that child's.
If a 4-year-old's weight at a checkup falls in the 20th percentile, that reading will be plotted between the curves for the 10th and 25th percentiles. That means 80% of children that age weigh more and 20% weigh less than that child.
Now, you shouldn't assume that a high or low reading means there's a problem. A baby whose head circumference is in the 90th percentile might also fall in the 90th percentile for weight and length - he's just a normal kid who's large overall. (He could be the son of a 6-foot, 8-inch former linebacker!)
The child whose weight falls in the 20th percentile may have parents who are a bit below average for height and weight. For him, 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 stature (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 affecting the child's growth.
What Can the Charts Tell Me About My Child's Growth?
Although growth charts are valuable tools, both doctors and parents must be careful not to focus too much on any one reading. Instead, the numbers should be viewed as a trend. Any measurement, taken out of context of the others, might give you the wrong impression of your child's growth. For example, a child's height measurement might place him at the 5th percentile, but this usually doesn't indicate a growth problem if his subsequent measurements continue to track along that percentile curve (as might be the case for a child who has inherited "short genes" from his parents). If the doctor and parents fixate on that one measurement, however, they might wrongly worry about the child's growth.
When growth chart readings are examined over time, they reveal a pattern of development. That pattern lets you know how your child is growing in relation to other children his age and also shows you how he has progressed from previous measurements. This information is a much more useful indicator of whether a child is growing normally than any single measurement.
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