Some U.S. schools are calculating students' BMI or weight-to-height ratios in an effort to fight childhood obesity. (Steve Miller/Associated Press)

Parents often ask pediatricians to see their children's growth chart but many don't seem to know how to interpret the information, a new U.S. study suggests.

In an online survey of 1,000 parents, 64 per cent of respondents said it was important to look at growth charts to see how their child was growing, and 40 per cent said they needed to see it to confirm what the health-care provider said verbally.

But only 64 per cent could tell a child's weight when shown it plotted on a growth chart in response to multiple-choice questions, Dr. Elana Pearl Ben-Joseph of Nemours Center for Children's Health Media in Wilmington, Del., and her colleagues reported in the October issue of the journal Pediatrics.

"Although growth charts are used frequently as visual aids to educate parents about their children's growth, many parents cannot comprehend the data," the study's authors concluded.

"This finding is significant because many parents prefer to be shown growth charts by their health-care provider, and many parents report recording their children's measurements on growth charts at home."

About one-third of parents could find a child's age, weight and percentile on a chart and define percentile correctly. Percentiles are used on a growth chart to show how a child compares to his or her peers.

For example, if a girl who is in the 90th percentile for height, she is taller than 90 per cent of other children her age. If a boy is in the 30th percentile for weight then 70 per cent of children his age weigh more than him.

Clothing sizes

The U.S. Centers for Disease Control and Prevention, World Health Organization and pediatric health-care groups in Canada encourage parents to use growth charts as monitoring tools. The Canadian Pediatric Society is currently updating its guidelines on growth charts.

The findings showed a well-proportioned short and light child was fretted about. However, just over half of parents were unconcerned about a very overweight child in the 10th percentile for height and 90th percentile for weight, Anjali Jain of the Children's National Medical Center in Washington said in a journal commentary accompanying the study.

"There is something real and important going on here — something that, despite the overgrowth of children that is characteristic of the obesity epidemic and the sprouting of adult-type cardiovascular diseases in children related to excess weight, makes parents still more worried about underweight than overweight, even now," Jain wrote.

Since the two dimensional lines and plots are not speaking a language that parents understand, Jain suggested using other approaches to getting parents to see when a child is underweight, overweight or obese, such as measuring abdominal circumference or discussing weight in terms of clothing size.

Previously, Canadian researchers have expressed concerns over whether standardized growth charts that were based on European newborns reflect healthy growth for babies of south or Chinese ancestry.