Are BMI-for-age and weight-for-length the same?
You may wonder whether
BMI-for-age and weight-for-stature are equivalent measures of overweight
and underweight. The NCHS growth charts of 1977 showed weight-for-length
of young children and weight-for-stature of older ones. In the revised
charts of 2000, the charts for birth to 36 months still show weight-for-length;
the charts for 2 to 20 years show BMI-for-age. Weight-for-stature is available
for children whose heights are between 77 and 121 cm (approximately 2-5
year olds) on optional charts.
A study at CDC (Mei et al.) evaluated the ability of those two measures to identify children as underweight (less than the 15th percentile) or overweight (greater than the 85th percentile) with low and high percentages of body fat. The study found that the two measures were equally valid for children aged 2-5 years, but the BMI-for-age was slightly better for older children and adolescents. Thus, under 24 months, weight-for-length is recommended; between 2 and 5 years, use either measure (CDC recommends using BMI-for-age after 2 years of age). For children age six years and over, use BMI-for-age.