In April 2006, the World Health Organization (WHO) released the WHO Child Growth Standards to replace the widely used National Center for Health Statistics (NCHS)/WHO reference population. Studies have shown important differences between these two references populations, especially during infancy. However, this reference population has not yet been widely used and is therefore not reflected in the current estimates of child malnutrition. It is likely that for some time to come the anthropometric indicators will have to be analyzed using both the NCHS/WHO and the new WHO Child Growth Standards, to allow for comparability with past estimates.
One main limitation of using anthropometry in assessing child nutritional status is its lack of specificity, as changes in body measurements are sensitive to many factors including intake of essential nutrients, infection, altitude, stress, and genetic background.
The underweight indicator reflects body mass relative to chronological age and is influence both by the height of the child, and weight-for-height. Its composite nature complicates its interpretation. For example, the indicator fails to distinguish between short children of adequate body weight and tall, thin children.
The accuracy of these nutrition measures depends on proper measurements in age, weight, and height. For example, only those children with month and year of birth recorded and with valid height and weight measurements are included in the calculations. Assessing the adherence to proper measurement protocols by each survey team is not possible.
Underweight prevalence is a useful indicator to assess overall nutritional status of the population. Stunting, or low height for age, is also a useful indicator for tracking trends in child malnutrition. It is defined as the percentage of children under five whose heights are less than two standard deviations below the median height for the age of the standard reference population. Stunting measures the cumulative deficient growth associated with long-term factors, including chronic insufficient daily protein intake.
Low weight for height, or wasting, defined as less than two standard deviations below the median weight for height of the reference population, indicates in most cases a recent and severe process of weight loss, often associated with acute starvation or severe disease.
When possible, all three indicators (underweight, stunting, and wasting) should be analysed and presented since they measure and reflect different aspects of child malnutrition.