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Differences in Methodology

Different approaches were used to construct the 2000 CDC and 2006 WHO growth charts for children from birth up to 2 years  and include differences in the

  • Data sources.
  • Type and frequency of data collection.
  • Sample sizes.
  • Exclusion criteria.
  • Breastfeeding rates among infants in the sample.
  • Use of cross-sectional data to construct the CDC charts versus longitudinal data to construct the WHO growth charts.
Comparison of sample populations used to create the CDC and WHO growth curves for children younger than aged 2 years
 CDC Growth Reference (2000)WHO Growth Standard (2006)
Data sources
  • National vital statistics (birthweight)
  • Missouri and Wisconsin vital statistics (birth length)
  • Pediatric Nutrition Surveillance System
    (length, 0.1 to <5 mos)
  • NHANES I (1971-74): 12-23 mos
  • NHANES II (1976-80): 6-23 mos
  • NHANES III (1988-94): 2-23 mos
Multicenter Growth Reference Study (longitudinal component)
Type and frequency of  data collectionCross-sectional data on weight and length starting at age 2 mos, with mathematical models used to connect birth weights and lengths to survey dataLongitudinal data with measurements of weight and length at birth; 1, 2, 4, 6, and 8 weeks; and 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 16, 18, 20, 22, and 24 mos
Sample size4,697 observations for 4,697 distinct children18,973 observations for 903 distinct children
Exclusion criteriaVery low birth weight  (<1,500 g [<3 lbs, 4 oz])
  • Low socioeconomic status
  • Born at altitude >1,550
    m/4,921 f
  • Birth at <37 wks or >42 wks
  • Multiple births
  • Perinatal morbidities
  • Child health conditions known to affect growth
  • Mother smoked during pregnancy or lactation
  • Breastfeeding <12 mos
  • Introduction of complementary foods before age 4 mos or after 6 mos
  • Weight-for-length measurements >3
    standard deviations above or below study median for sex
Infant feeding50% ever breastfed
33% breastfed at 3 mos
  • 100% ever breastfed
  • 100% predominantly breastfed at 4 mos
  • 100% breastfed at 12 mos
  • Complementary foods introduced at mean age of 5.4 mos

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