| Popis: |
Background: Growth is volatile and non-linear. Assessing the instantaneous speed of growth (momentary height velocity) depends on the precision and the number of measurements and the duration of the observation period. Measurements at short intervals reflect both the non-linearity of growth and the technical error of measurements (TEM). Material: We reanalyzed longitudinal measurements of body length at age 0, 3 months, 6 months, 9 months, 12 months, 18 months, and 24 months, from 1879 healthy infants (956 girls, 923 boys) from France (180 girls, 173 boys), Vilnius, Lithuania (507 girls, 507 boys), Lublin, Poland (67 girls, 56 boys), Zurich, Switzerland (94 girls, 102 boys) and Spain (108 girls, 95 boys); and longitudinal measurements of annual body height from age 2 to 18 years from 1528 healthy children and adolescents (774 girls, 754 boys) from France (41 girls, 47 boys), Vilnius, Lithuania (23 girls, 27 boys), Lublin, Poland (70 girls, 58 boys), Zurich, Switzerland (111 girls, 120 boys), Spain (94 girls, 74 boys), the Czech Republic (65 girls, 69 boys), Hungary (316 girls, 320 boys), and Berkeley, USA (54 girls, 39 boys). Results: We calculated age- and sex-specific mean values for height and SD for height separately for each country. In addition, we defined the instantaneous speed of growth by the dhSDS(t) difference of two measures of hSDS (v(hSDS(t)) = Delta hSDS(t)/t), or in the case of multiple measurements, by the slope of the linear regression (BhSDS((t))). Based on the longitudinal measurements of body length, we present reference values for annual growth velocity given in the form of SD of annual hSDS changes (Delta hSDS), from birth to maturity. Correction factors are added for validating measurements obtained at intervals of less than one year. The correction factors depend on number of measurements, and duration of the observation period. |
