Classification of obesity in children

There is currently no generally accepted classification of obesity in children. In adults, the diagnosis of obesity is based on the calculation of BMI [the ratio of body weight (in kilograms) to a person's height (in meters) squared]. BMI can overestimate the obesity of trained athletes or muscular children, but BMI calculation is the most reliable and accurate method for determining excess body weight. Other methods for assessing obesity are also used, but they are either very expensive (ultrasound, CT, MRI, X-ray absorptiometry), or require special equipment (calipers), or are poorly reproducible (measuring waist and hip volume), or have no standards for childhood (bioelectrical impedance analysis).

In children, the BMI indicator is assessed taking into account age and gender according to recommended standards. The body weight norm is taken as its value for the corresponding age. These standards are recommended by WHO (Expert Committee on Clinical Guidelines for Overweight in Adolescent Preventive Services and European Childhood Obesity Group) as a criterion for determining excess body weight in childhood.

Currently, anthropometric indicators are assessed mainly in two ways: parametric, or sigma, and non-parametric - dental.

The parametric scale includes the arithmetic mean ("norm") and deviations from it, measured by the "sigma" value (a isthe standard deviation - SD). To assess the degree of difference of the studied parameter from the average values, the standard deviation score (SDS) is calculated. The m±SD indicator is the area of average values, characteristic of approximately 68% of healthy children. The SDS value is from +1 to -1.

Excess body weight SDS corresponds to +1-+2, obesity in children - +2 and more. In the group of children with obesity, two subgroups are distinguished:

• moderate obesity - SDS = 2.02-2.35;
• morbid (severe) obesity - SDS = 2.36-3.52.

There are special programs, such as Growth Analyser 3.5, Dutch Growth Foundation, which evaluate in SDS units.

The advantage of the method is the ability to evaluate and describe pronounced deviations, most often characterizing endocrine pathology. Values in the range from +2 SD (SDS=+2) to -2 SD (SDS=-2) approximately correspond to values from the 97th to the 3rd centile.

Dental tables (or charts) show quantitative limits of height and body weight in a certain proportion, or percentage (centile), of children depending on age. Since the centile method is not limited by the nature of the distribution, it is applicable to assessing any indicators. The method is easy to use, since any calculations are excluded when using centile tables or charts.

Classification of body mass index in children and adolescents (WHO)

	BMI percentiles by age	Diagnosis
Less than 5		Underweight
5-84		Normal body weight
85-94		Overweight
95 and above		Obesity

For children of the first 2 years of life, percentile tables of growth, body weight, and head circumference standards are used separately for girls and boys, compiled on the basis of measurements of a representative cohort of children of the European population. The growth and body weight indicators obtained on the specified population of children are fully consistent with the data of I.M. Mazurin et al., obtained during a survey of the Russian population of children.

Growth percentiles (body weight, head circumference) are average values (the median value corresponds to the 50th percentile) and deviations from the median, the 3rd percentile corresponds to the lower limit of the norm (-2 SD from the mean value), and the 97th percentile corresponds to the upper limit of the norm (+2 SD from the mean value).

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