Last month I stressed the importance of growth curves in pediatrics as a sensitive indicator of health in growing children. In this issue, we’ll consider some tips and important red flags in their use.

Good measurement

Measuring a child should be done as accurately as possible. Calculating the weight is relatively easy with standard medical scales. Length and height measurements should be made using a rigid device that can lock. Stadiometers are extremely accurate and can be obtained for a moderate price.

Using a tape measure is notoriously inaccurate and should be avoided. Remember to plot the height on the 0-36 months chart when the measurement is obtained with the youngster lying down; use the 2-18 year chart if the measurement is taken with the child standing. Head circumference should be obtained for all kids to the age of at least two, and beyond if there’s any concern, for example about hydrocephalus. The head circumference assessment should be plotted on the Nellhaus chart (birth to 18 years). I’ve found this head circumference chart to be much more sensitive than the one found on the reverse side of the CDC charts. I’m always astounded at how a child’s growth consistently follows a particular growth channel determined by genetic factors.

On the reverse side of the newer CDC curves, BMI is plotted against age. A kid whose BMI is between the 85^th and 95^th percentiles is overweight; a child is obese when the BMI plots greater than the 95^th percentile. It’s important to plot the BMI against age because the absolute number has a very different meaning than when using adult standards. For example, a BMI of 22 would be considered normal for an adult, but would classify a 7-year-old as obese. A BMI of 15, considered unhealthy in an adult, would place a 6-year-old at the 50^th percentile for age and be considered normal.

More tips

The trajectory of growth is always more valuable than a single point on the curve. So it’s always advisable to weigh and measure an infant/child/adolescent at every well visit. When seeing a young patient for the first time it’s always wise to ask the parents for previously obtained growth parameters, which you can use to construct the growth trajectory. A child who’s consistently following their curve for height and weight will rule out any significant chronic illness. One point to keep in mind is that an infant may start life at a high percentile but by 6 or 9 months will have fallen to a lower one, sometimes crossing more than two percentile lines. He or she then stays on that particular growth percentile. This is perfectly normal because early growth may represent intrauterine growth factors. These can persist in early infancy, but the child then finds his genetically determined channel of growth and remains there.

Special cases

There are growth curves standardized against different populations which are useful when following children with certain genetic conditions. For example, there are standard curves for children with trisomy 21, Turner’s syndrome, achondroplasia, and different ethnic groups. These can be downloaded from various internet sites. There are also growth charts for premature infants that take into account gestational age.

It’s always useful to plot the parents’ heights on the child’s growth curve to give some indication of expected adult height. Predicted adult heights are usually within 10 cm of midparental height. For boys, add 6.5 cm to midparental height and for girls subtract 6.5 cm to obtain a ‘target’ height.

Ideal body weight

When I see overweight or obese children, I’m often asked how much weight they need to lose. Again, the growth curve is helpful because one can extrapolate the weight percentile to the corresponding height percentile to give a rough estimate of ideal body weight. Fortunately, children can ‘grow into’ their height percentile, unlike adults who only grow circumferentially!

A fall off in the weight curve of infants is generally due to inadequate caloric intake. This may have many causes including chronic illness. I’ve often seen curves where the patient falls off his or her weight curve during the 12-24 month period when children are picky eaters but regains their original channel of growth some months later. Sometimes this can be quite dramatic. Organic causes of failure to thrive are rare and when you see a child who has fallen off his weight curve it’s rarely necessary to do an extensive investigation for causes. Careful attention to caloric intake and assiduous follow-up is usually all that’s necessary in an otherwise healthy kid. The ‘fat dwarf’ — that is, a child who’s gaining weight appropriately but falling off the height curve — should alert you to a possible endocrine cause e.g. hypothyroidism or growth hormone deficiency.

A final note

The growth curves we use average out the adolescent growth spurt and therefore the measurements you obtain should be compared with the Tanner staging of the adolescent.

In conclusion, accurate measurements of growth parameters plotted on an appropriate growth curve is one of the simplest but most powerful tools in our care of infants, children and adolescents.