Assessment of nutritional status and early child development

To measure children’s nutritional status, the survey included anthropometric indicators and hemoglobin level to identify the presence of anemia, and blood concentration of vitamin A and iron to identify micronutrient deficiencies. Child growth indicators and standardized scores (z-scores) were constructed following the World Health Organization (WHO) guidelines [17] for the three most common anthropometric indices: height for age, weight for age, and weight for height. The z-score system expresses the anthropometric value as the number of standard deviations from the median of the WHO reference population^7,8. In addition, we computed indicators of prevalence of chronic malnutrition (stunting), underweight, and overweight, based on height for age and weight for age standard cutoff values of below or above two standard deviations from the reference median.

To measure anemia the ESNUT obtained levels of hemoglobin in blood for each child between 3 and 59 months using a HemoCue® test for the photometric detection of hemoglobin. This method has been used extensively in household surveys in developing countries, including the Demographic and Health Surveys. Presence of mild, moderate or severe anemia was then determined based on altitude-adjusted hemoglobin levels and standard cutoff values⁹.

One of ESNUT’s specific objectives was to assess deficits of key micronutrients in small children; specifically, vitamin A deficiency (VAD) and iron deficiency (ID). To measure VAD and ID, blood samples were obtained from a subsample of 2,000 children ages 6 to 23 months using the Dried Blood Spots (DBS) method. This method collects a few blood drops from a heel or finger prick that are then impregnated in filter paper and let to dry¹⁰. All DBS were rehydrated and analyzed in a laboratory using the Enzyme-Linked Immunosorbent Assay method (ELISA)¹¹ [18]. The indicators to estimate concentration of Vitamin A and iron were the Retinol Binding Protein (RBP) and the Free Transferrin Receptor (sTfR), respectively. VAD was defined as RBP below 0.7μmol/l [19] and ID as sTfR above 8.3 mg/l. Excluding samples with low quality (damaged or small blood spots) and with indication of inflammation, the total sample size for micronutrient analysis was 1,655¹².

Early child development was assessed through measures of gross motor and communicative development. The ESNUT used 11 age-specific survey questionnaires for children between 3.5 and 36.5 months¹³ which were based on the second edition of the Ages and Stages Questionnaires® (ASQ-2)¹⁴. The questionnaires contained items about tasks that the child is (or is not) able to perform according to his or her age. Most items were reported by the child’s caregiver, while some specific items were based on direct observation of the child. To increase scores’ variability, the survey added items of decreasing and increasing difficulty. Similar adaptations have been used in other studies [20–22]. The questionnaires’ language was adapted to the local context of Bolivia.

Each item had a score of 10, 5 or 0 depending on whether the child can perform the task always, sometimes, or never, respectively. Raw scores were constructed for each domain as the sum of scores across items. Because the population on which the ASQ was standardized (US children) was not considered an appropriate reference population for our sample, we constructed within sample or internally standardized scores adjusted by age. Following standard procedures, internal z-scores were constructed within the eleven age groups to have a mean of 0 and a SD of 1 (by subtracting the age-group specific mean of the raw score and dividing by the age-group specific SD).