Normal Growth

Dr. Greene's Answer

Childhood is a magical time. What is the essence of childhood? Is it wonder? Innocence? Security? . . .

The essence of childhood is growth. Growth defines childhood for all species. Growth creates the magic and the wonder. Of course some adults retain a sense wonder — those who continue to flower and grow.

Since growing is the core task of childhood, assessing growth is an important part of pediatrics. One of the major reasons for those numerous well-child check ups is to carefully measure and follow growth over time. Each time a young child visits her doctor, her height, weight, and head circumference are measured and recorded on a growth chart.

These charts were created from data collected between 1963 and 1975 as part of the Fels Longitudinal Study conducted by Wright State University School of Medicine in Yellow Springs, Ohio. More than 20,000 healthy, well-nourished, American children were measured to determine normal growth rates. In 1979, the National Center for Health Statistics (NCHS) published these values as reference numbers for children in the U.S. The World Health Organization (WHO) later adopted these same numbers as the international standard for growth.

The NCHS growth charts are divided into seven percentile lines, ranging from the 5th to 95th percentile. If a girl, such as Siobhan, is at the 75th percentile in height, it does not mean that her height is 75 percent of normal. Rather it means that Siobhan is taller than 75 percent of the healthy, well-nourished girls her age in the Ohio Study between 1963 and 1975. The 50th percentile is the median, or standard value — the number above and below which half of the children fall.

Siobhan’s height, weight, and head circumference are all normal for her age. Numbers between the 5th and 95th percentiles are considered normal. The standard weight for a one-year-old girl is 21 pounds. Anyone weighing between 17 1/4 and 24 3/4 pounds will be between the 5th and 95th percentiles. Nevertheless, remember that, by definition, 5 percent of completely healthy, well-nourished girls will fall below the 5th percentile. Still, when a child measures below the 5th percentile, the likelihood that there is some type of growth problem increases.

The NCHS charts not only determine normal height, weight, and head circumference for age, but also provide values of appropriate weight for each given height, regardless of age. Since she was 2 months old, Siobhan’s weight for height has fallen between the 5th and 10th percentiles. Between five and 10 percent of healthy, well-nourished children of her height weigh less than she does. She is thin — but not abnormally thin.

So far we have been looking at where a child falls on the growth chart at any given moment — but growth is a process, not a moment in time. A girl at the fifth percentile in weight may be growing normally, may be experiencing growth failure, or may be having a growth spurt, depending on the trajectory of her growth curve. The first few points of a growth curve primarily reflect the in utero environment. Once a child is a few months old, however, the curves begin to reflect her own genetic tendencies, as well as the impact of her own nutrition and health. Rapid changes in percentile lines may signal a problem. If Siobahn’s weight and head circumference proceed to fall below the 5th percentile, it will be prudent to determine why.

Broadly speaking, children who are too small may be so for one of 5 reasons — congenital, familial, constitutional, hormonal, or nutritional:

• Congenitally small children are born small, and the growth tapers off during infancy. The underlying problem might be a chromosomal abnormality (such as Down’s syndrome), a congenital infection (such as herpes), or a toxic exposure (such as alcohol or tobacco).
• Children small for familial reasons have small parents.
• In constitutional growth delay, children are born at an average size, drop to lower percentiles during infancy, and then follow these curves through childhood, with an extra growth spurt during adolescence. These children become normal size adults. This pattern may run in families (it does in mine).
• Children with hormonal growth failure will have normal or increased weight for height. Their heights will decline before, or at the same time as, weights.
• In nutritional problems, by contrast, the weight falls first (called wasting), perhaps followed eventually by the height (called stunting), and sometimes leading eventually to a decreasing head size (severe, chronic malnutrition). Nutritional problems can be the result of inadequate intake, increased caloric needs (heart disease, kidney disease), or the inability to use calories consumed (extreme social/emotional deprivation).

I can’t possibly assess your daughter without having examined her. I can say, however, that a child with a growth pattern like your daughter’s might be growing completely normally, might have a constitutional growth delay, or might need some extra nutrition. A careful history and physical examination by her pediatrician, with particular attention to her overall development and nutritional status, should help illuminate the situation. Tell Siobhan happy birthday from me, and may we all grow in wonder this coming year!