BMI-for-age Z-score Research Articles

Height for Age Increased While Body Mass Index for Age Remained Stable between 1968 and 2007 among Guatemalan Children

Promotion of optimal growth while preventing the emergence of obesity in childhood requires an understanding of the dynamics over time of linear growth and weight for height. To assess long-term secular trends in height-for-age and BMI for age in children <6 y old, we analyzed a series of cross-sectional surveys conducted between 1968 and 2007 in 4 villages in eastern Guatemala. We used height and weight of children <6 y old (n = 507, 606, 627, 704, 526, and 502 for survey years 1968, 1972, 1977, 1988, 1997, and 2005-7, respectively) to compute height-for-age Z-score (HAZ) and BMI-for-age Z-score (BMIZ) based on WHO growth standards. HAZ was -2.73 +/- 1.12 (mean +/- SD) in 1968 and -1.16 +/- 1.16 in 2005-7 (P < 0.001). The prevalence of stunting (HAZ <-2.0) was 73.0% in 1968 and 23.1% in 2005-7 (P < 0.001). Among children 57-63 mo old, HAZ in 2005-7 was 1.20 (95% CI, 0.79, 1.62) SD units higher than in 1968, corresponding to 5.6 cm in boys and 5.7 cm in girls. For all survey years except 2007, BMIZ increased through age 36 mo, then declined; for the 2005-7 sample, BMIZ did not vary by age. The prevalence of BMIZ >1.00 was 21.1% in 1968 and 19.6% in 2005-7 (P > 0.05); for BMI <-1.00, the respective prevalences were 7.9% and 5.2% (P > 0.05). There have been long-term improvements in child growth, as measured by HAZ, without concurrent increases in BMI over successive generations of children.

Standard deviation of anthropometric Z-scores as a data quality assessment tool using the 2006 WHO growth standards: a cross country analysis

Height- and weight-based anthropometric indicators are used worldwide to characterize the nutritional status of populations. Based on the 1978 WHO/National Center for Health Statistics (NCHS) growth reference, the World Health Organization has previously indicated that the standard deviation (SD) of Z-scores of these indicators is relatively constant across populations, irrespective of nutritional status. As such, the SD of Z-scores can be used as quality indicators for anthropometric data. In 2006, WHO published new growth standards. Here, we aim to assess whether the SD of height- and weight-based Z-score indicators from the 2006 WHO growth standards can still be used to assess data quality. We examined data on children aged 0-59 months from 51 Demographic and Health Surveys (DHS) in 34 developing countries. We used 2006 growth standards to assign height-for-age Z-scores (HAZ), weight-for-age Z-scores (WAZ), weight-for-height Z-scores (WHZ) and body-mass-index-for-age Z-scores (BMIZ). We also did a stratified analysis by age group. The SD for all four indicators were independent of their respective mean Z-scores across countries. Overall, the 5th and 95th percentiles of the SD were 1.35 and 1.95 for HAZ, 1.17 and 1.46 for WAZ, 1.08 and 1.50 for WHZ and 1.08 and 1.55 for BMIZ. Our results concur with the WHO assertion that SD is in a relatively small range for each indicator irrespective of where the Z-score mean lies, and support the use of SD as a quality indicator for anthropometric data. However, the ranges of SDs for all four indicators analysed were consistently wider than those published previously by WHO.