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The CDC released new on Thursday to include children and adolescents with severe obesity.

Charts now extend to a BMI of 60, and severe obesity is defined as 120% of the 95th percentile, to reflect the higher prevalence of obesity among kids and teens, rates of which have .

These new curves were added to the pre-existing 2000 CDC BMI-for-age growth charts, which stopped at a BMI of 37, with separate charts for males and females ages 2 to 20. Otherwise, the charts remain unchanged.

"As a clinician, I encourage healthcare providers to use the extended growth charts as a tool when working with children and adolescents with severe obesity," said Karen Hacker, MD, MPH, director of the CDC's National Center for Chronic Disease Prevention and Health Promotion.

"Intervening early is critical to improving the health of our children as they grow into adults. Prior to today's release, the growth charts did not extend high enough to plot BMI for the increasing number of children with severe obesity," Hacker explained in a statement. "The new growth charts coupled with high-quality treatment can help optimize care for children with severe obesity."

Prior to this change, the BMI-for-age curves stopped at the 97th percentile owing to the fact that there were too few young people with these very high BMI values. With obesity rates drastically increasing over the past few decades -- more than 4.5 million children and adolescents had severe obesity in 2018 -- the CDC made the call to extend the charts.

The 2000 CDC growth charts were created based on national survey data from children and adolescents from 1963 to 1980, long before the uptick in pediatric obesity. The newly added percentiles are based on data for children with obesity from 1998 through 2016.

The CDC also released extended BMI z-score charts associated with the extended percentiles.

"With very high BMI values above the extended 99th percentile, the z-score may be an easier number for clinicians, patients, and families to understand," the CDC's guide on the extended growth charts noted.

"For example, the value of z-score=1 is nearly equivalent to the 85th percentile -- the threshold for overweight status. A z-score of 4 is equivalent to the extended 99.9th percentile, but z-scores of 4 and 1 may be easier to convey to patients and families compared to extended 99.9th and 85th percentiles."

In order to help healthcare professionals with these revised calculations, the CDC is referring to its to crunch the percentiles and z-scores for a child's sex and age for BMI, weight, height, and head circumference.

Other than this change, the CDC said that there are no plans to completely overhaul the growth charts with current data because it would skew the charts, essentially normalizing obesity.

"Using a new 95th percentile to define obesity would lead to some children being below the 95th percentile who were above using the 2000 charts," the agency noted.

"As an example, during 2017-March 2020, 19.7% of U.S. children and adolescents were above the 95th percentile of the 2000 CDC BMI-for-age growth charts and had obesity. If the charts were updated to include only these children, 5%, not 19.7%, would be above the 95th percentile."

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