Relationship between physical growth and motor development in the WHO Child Growth Standards

Aim: To examine relationships among physical growth indicators and ages of achievement of six gross motor milestones in the WHO Child Growth Standards population. Methods: Gross motor development assessments were performed longitudinally on the 816 children included in the WHO Child Growth Standards. Six milestones (sitting without support, hands-and-knees crawling, standing with assistance, walking with assistance, standing alone, walking alone) were assessed monthly from 4 until 12 mo of age and bimonthly thereafter until children could walk alone or reached 24 mo. Failure time models were used 1) to examine associations between specified ages of motor milestone achievement and attained growth z scores and 2) to quantify these relationships as delays or accelerations in ages of milestone achievement. Results: Statistically significant associations were noted between ages of achievement of sitting without support and attained weight-for-age, weight-for-length and BMI-for-age z scores. An increase of one unit z score in these indicators was associated with 3 to 6 d acceleration in the respective achievement age. Statistically significant associations also were noted between various milestone achievement ages and growth when 3- or 6-mo and birth length-for-age z scores were entered jointly in the failure time models. In these analyses, one unit z-score increase in length-for-age was associated with 1 to 3 d delay in the respective achievement age.
Conclusion: Sporadic, significant associations were observed between gross motor development and some physical growth indicators, but these were quantitatively of limited practical significance. These results suggest that, in healthy populations, the attainment of these six gross motor milestones is largely independent of variations in physical growth.     

Reliability of anthropometric measurements in the WHO Multicentre Growth Reference Study

Aim: To describe how reliability assessment data in the WHO Multicentre Growth Reference Study (MGRS) were collected and analysed, and to present the results thereof.
Methods: There were two sources of anthropometric data (length, head and arm circumferences, triceps and subscapular skinfolds, and height) for these analyses. Data for constructing the WHO Child Growth Standards, collected in duplicate by observer pairs, were used to calculate inter-observer technical error of measurement (TEM) and the coefficient of reliability. The second source was the anthropometry standardization sessions conducted throughout the data collection period with the aim of identifying and correcting measurement problems. An anthropometry expert visited each site annually to participate in standardization sessions and provide remedial training as required. Inter- and intra-observer TEM, and average bias relative to the expert, were calculated for the standardization data.
Results: TEM estimates for teams compared well with the anthropometry expert. Overall, average bias was within acceptable limits of deviation from the expert, with head circumference having both lowest bias and lowest TEM. Teams tended to underestimate length, height and arm circumference, and to overestimate skinfold measurements. This was likely due to difficulties associated with keeping children fully stretched out and still for length/height measurements and in manipulating soft tissues for the other measurements. Intra- and inter-observer TEMs were comparable, and newborns, infants and older children were measured with equal reliability. The coefficient of reliability was above 95% for all measurements except skinfolds whose R coefficient was 75–93%.
Conclusion: Reliability of the MGRS teams compared well with the study's anthropometry expert and published reliability statistics.     

WHO Child Growth Standards based on length/height, weight and age

Aim: To describe the methods used to construct the WHO Child Growth Standards based on length/height, weight and age, and to present resulting growth charts. Methods: The WHO Child Growth Standards were derived from an international sample of healthy breastfed infants and young children raised in environments that do not constrain growth. Rigorous methods of data collection and standardized procedures across study sites yielded very high-quality data. The generation of the standards followed methodical, state-of-the-art statistical methodologies. The Box-Cox power exponential (BCPE) method, with curve smoothing by cubic splines, was used to construct the curves. The BCPE accommodates various kinds of distributions, from normal to skewed or kurtotic, as necessary. A set of diagnostic tools was used to detect possible biases in estimated percentiles or z-score curves. Results: There was wide variability in the degrees of freedom required for the cubic splines to achieve the best model. Except for length/height-for-age, which followed a normal distribution, all other standards needed to model skewness but not kurtosis. Length-for-age and height-for-age standards were constructed by fitting a unique model that reflected the 0.7-cm average difference between these two measurements. The concordance between smoothed percentile curves and empirical percentiles was excellent and free of bias. Percentiles and z-score curves for boys and girls aged 0–60 mo were generated for weight-for-age, length/height-for-age, weight-for-length/height (45 to 110 cm and 65 to 120 cm, respectively) and body mass index-for-age.
Conclusion: The WHO Child Growth Standards depict normal growth under optimal environmental conditions and can be used to assess children everywhere, regardless of ethnicity, socio-economic status and type of feeding.     

Development of a WHO growth reference for school-aged children and adolescents

OBJECTIVE: To construct growth curves for school-aged children and adolescents that accord with the WHO Child Growth Standards for preschool children and the body mass index (BMI) cut-offs for adults. METHODS: Data from the 1977 National Center for Health Statistics (NCHS)/WHO growth reference (1-24 years) were merged with data from the under-fives growth standards' cross-sectional sample (18-71 months) to smooth the transition between the two samples. State-of-the-art statistical methods used to construct the WHO Child Growth Standards (0-5 years), i.e. the Box-Cox power exponential (BCPE) method with appropriate diagnostic tools for the selection of best models, were applied to this combined sample. FINDINGS: The merged data sets resulted in a smooth transition at 5 years for height-for-age, weight-for-age and BMI-for-age. For BMI-for-age across all centiles the magnitude of the difference between the two curves at age 5 years is mostly 0.0 kg/m(2) to 0.1 kg/m(2). At 19 years, the new BMI values at +1 standard deviation (SD) are 25.4 kg/m(2) for boys and 25.0 kg/m(2) for girls. These values are equivalent to the overweight cut-off for adults (> or = 25.0 kg/m(2)). Similarly, the +2 SD value (29.7 kg/m(2) for both sexes) compares closely with the cut-off for obesity (> or = 30.0 kg/m(2)). CONCLUSION: The new curves are closely aligned with the WHO Child Growth Standards at 5 years, and the recommended adult cut-offs for overweight and obesity at 19 years. They fill the gap in growth curves and provide an appropriate reference for the 5 to 19 years age group.     

Correlation between thrombin potential and bleeding after cardiac surgery in adults.

We used a sensitive assay to measure thrombin potential in 20 patients who underwent cardiopulmonary bypass surgery for coronary artery bypass grafts. We measured coagulation factors II, V, VII, VIII and X. Blood loss was measured as the total amount in the mediastinal drains in the first 24 h postoperatively. Thrombin potential was median 107 nmol/l.min (range 62-181) preoperatively and median 46 nmol/l.min (range 19-120) postoperatively. Coagulation factors II, V, VII,VIII and X were within normal limits preoperatively. Factor II fell from 77 IU/dl preoperatively to 37 IU/dl at 120 min postoperatively. Factor V fell from 85 IU/dl preoperatively to 61 IU/dl postoperatively. Factor VII fell from 91 IU/dl to 66 IU/dl postoperatively. Factor VIII was 128 IU/dl preoperatively and 127 IU/dl postoperatively. Factor X fell from 90 IU/dl preoperatively to 50 IU/dl postoperatively. Total blood loss in 24 h in the mediastinal drains postoperatively was mean 673 ml, median 650 ml (range 250-2000). Reduction in thrombin potential correlated inversely with postoperative blood loss, r= -0.75 (Spearman correlation). The fall in the thrombin potential correlated with the prothrombin level (r = 0.75) and factor X (r = 0.47).     

Assessment of differences in linear growth among populations in the WHO Multicentre Growth Reference Study

Aim: To assess differences in length/height among populations in the WHO Multicentre Growth Reference Study (MGRS) and to evaluate the appropriateness of pooling data for the purpose of constructing a single international growth standard. Methods: The MGRS collected growth data and related information from 8440 affluent children from widely differing ethnic backgrounds and cultural settings (Brazil, Ghana, India, Norway, Oman and the USA). Eligibility criteria included breastfeeding, no maternal smoking and environments supportive of unconstrained growth. The study combined longitudinal (birth to 24 mo) and cross-sectional (18–71 mo) components. For the longitudinal component, mother–infant pairs were enrolled at delivery and visited 21 times over the next 2 y. Rigorous methods of data collection and standardized procedures were applied across study sites. We evaluate the total variability of length attributable to sites and individuals, differences in length/height among sites, and the impact of excluding single sites on the percentiles of the remaining pooled sample. Results: Proportions of total variability attributable to sites and individuals within sites were 3% and 70%, respectively. Differences in length and height ranged from −0.33 to +0.49 and −0.41 to +0.46 standard deviation units (SDs), respectively, most values being below 0.2 SDs. Differences in length on exclusion of single sites ranged from −0.10 to +0.07, −0.07 to +0.13, and −0.25 to +0.09 SDs, for the 50th, 3rd and 97th percentiles, respectively. Corresponding values for height ranged from −0.09 to +0.08, −0.12 to +0.13, and −0.15 to +0.07 SDs.
Conclusion: The striking similarity in linear growth among children in the six sites justifies pooling the data and constructing a single international standard from birth to 5 y of age.     

Construction of the World Health Organization child growth standards: selection of methods for attained growth curves

The World Health Organization (WHO), in collaboration with a number of research institutions worldwide, is developing new child growth standards. As part of a broad consultative process for selecting the best statistical methods, WHO convened a group of statisticians and child growth experts to review available methods, develop a strategy for assessing their strengths and weaknesses, and discuss methodological issues likely to be faced in the process of constructing the new growth curves. To select the method(s) to be used, the group proposed a two-stage decision-making process. First, to select a few relevant methods based on a list of set criteria and, second, to compare the methods using available tests or other established procedures. The group reviewed 30 methods for attained growth curves. Using the pre-defined criteria, a few were selected combining five distributions and two smoothing techniques. Because the number of selected methods was considered too large to be fully tested, a preliminary study was recommended to evaluate goodness of fit of the five distributions. Methods based on distributions with poor performance will be eliminated and the remaining methods fully tested and compared.