Term Infant Growth Tools

WHO Growth Tools, Birth to 2 Years

The AAP and Centers for Disease Control and Prevention recommend using the World Health Organization (WHO) growth tools to assess growth during the first 2 years after birth for term infants. 

WHO Growth Charts, Birth to 2 Years

The AAP and CDC recommend using the 2.3rd and 97.7th percentiles of the WHO growth curves (labeled as 2nd and 98th on the curves, or 2 SDs above and below the median) to identify children with potentially suboptimal growth in the first 24 months after birth.

• CDC has developed a training course for health care professionals who measure and assess growth using the WHO growth charts for children from birth to 2 years.

In brief, the WHO growth charts are constructed using

• Reference measures: weight for age, length for age, head circumference for age, weight for length, body mass index (BMI) for age.
• Reference data: prescriptive, cross-sectional, and longitudinal data from the WHO Multicentre Growth Reference Study, (ref) (ref) (ref) an international sample of healthy children with optimal conditions for growth (eg, breastfed). 

The WHO growth charts

• For term newborns, infants, and children (37-41 weeks gestational age).
  • Sex specific.
  • Do not provide gestational specific assignment of size for newborns.
  • 2nd to 98th percentiles.
• Weight-for-length comparisons are independent of age and can differentiate stunted growth from wasting.
  • Stunting results in a child who is proportional but small for age.
  • Causes of stunting are frequently constitutional but also can be caused by
    • Malnutrition
    • Chronic illness
    • Genetic or endocrine abnormalities
  • Weight-for-length measurement is recommended for full-term newborns, infants, and children through 2 years of age, although BMI may be a better indicator of excess relative weight in infants younger than 6 months.
    • At 2 months of age, BMI was shown to be a better predictor of obesity at 2 years than was weight for length.
• WHO growth charts (birth to 24 months)
  • Head circumference-for-age and weight-for-length percentiles (girls) (boys)
  • Length-for-age and weight-for-age percentiles (girls) (boys) 

Body Mass Index for Age

There is no accepted definition of underweight, overweight, or obesity for children younger than 2 years. 

• For infants, BMI charts are used to screen for overnutrition and malnutrition and are particularly relevant in term infants younger than 6 months.
  • A comparative study of nearly 74,000 full-term infants found consistent agreement between BMI and weight for length from 6 months onward.
• For preterm infants, BMI for age as a measure of disproportionality or as a proxy for body fat postnatally is not well established.
• WHO charts
  • BMI-for-age birth to 2 years percentiles (girls) (boys)
  • BMI-for-age birth to 2 years z scores (girls) (boys) 

Incremental Growth Charts

Growth occurs as a series of intermittent spurts that vary in magnitude according to age, sex, maturational status, and season. 

Nutritional status can be assessed by growth increments. 

• Growth increments are sensitive to the time interval between measurements because growth occurs as a series of intermittent small or large spurts that vary in magnitude according to age, sex, maturational status, and season. 
  • Comparison of a growth increment based on a longer or shorter interval than that used in the reference curve may overestimate or underestimate incremental growth status. 
  • Growth increments should be based on accurate growth measurements, carefully calculated, and compared with reference values based on similar time intervals.
  • The accuracy of growth increments depends on the accuracy and precision of the 2 measurements on which it is calculated. 

WHO Multicentre Growth Reference Study Incremental Growth Charts for 0 to 24 Months

• Reference measures: weight increment and velocity, length increment and velocity, head increment and circumference velocity
• Reference data: longitudinal data from an international sample of healthy children with optimal conditions for growth (eg, breastfed) 
• Comments
  • For ages 0 to 60 days: increments of 1 to 2 weeks for weight
  • For ages 0 to 12 months: increments of 1 month for weight
  • For ages 0 to 12 months: 2- and 3-month increments for head circumference
  • For ages 0 to 24 months: 4- and 6-month increments for head circumference
  • For ages 0 to 24 months: increments of 2 to 6 months for weight and length
  • For ages 0 to 24 months: 2- to 6-month increments for length
• Charts
  • Length velocity (2-, 3-, 4-, and 6-month increments)
  • Head circumference velocity (2-, 3-, 4-, and 6-month increments) 

Other Anthropometric Measures for Infants and Young Children

Mid-upper–arm circumference (MUAC) and skinfold thickness are alternate forms of assessing nutritional status.

Arm Circumference for Age 

Mid-upper–arm circumference is an indicator of soft tissue growth in all ages. MUAC can be useful as a screening tool in settings where determination of nutritional status is difficult.  

MUAC is an accurate predictor of child mortality. 

Measure the right arm at its midpoint using a flexible, non-stretchable tape measure.  

• Mark the upper arm midway between the acromion (shoulder) and the olecranon (elbow) on the vertical axis of the upper arm between the lateral and medial surface of the arm with the arm bent at a right angle. 
• For the actual circumference measurement, the arm should hang loosely at the side. Pass the tape around the arm at the level marked, perpendicular to the long axis of the arm.
• Position the tape so that it touches but does not compress the skin or alter the contour of the arm. 

WHO Multicentre Growth Reference Study 2006 and 2009 (ref) (ref)

• Reference data: cross-sectional and longitudinal data from an international sample of healthy children with optimal conditions for growth (eg, breastfed)     
• Comments
  • Age: 3 months to 5 years
    • Sex specific. 
    • 3rd to 97th percentile.
    • Use with triceps skinfold-for-age curves.
• Charts
  • Percentiles: arm circumference for age, 3 months to 5 years (girls) (boys)
  • Z scores: arm circumference for age, 3 months to 5 years (girls) (boys) 

Skinfold Thickness Measurements 

Total or regional body fat can be estimated using skinfold thickness. 

• Advantages
  • Easily and rapidly performed in the clinical setting.
  • Safe.
  • Reasonably accurate.
  • Inexpensive.
  • Excellent pediatric reference data are available.
• Disadvantages 
  • Unable to use in neonates due to lack of reference tables.
  • Training is required to get reproducible measurements.
• Reference charts in both curve and table formats
  • Curve: triceps skinfold for age, 3 months to 5 years, percentiles (girls) (boys)
  • Table: triceps skinfold for age, 3 months to 5 years, percentiles (girls) (boys)
  • Curve: triceps skinfold for age, 3 months to 5 years, z scores (girls) (boys)
  • Table: triceps skinfold for age, 3 months to 5 years, z scores (girls) (boys) 

CDC Growth Assessment Tools, >2 Years

The CDC growth charts can be used for children and teens aged 2 to 19 years. 

Use the corrected age of infants and children born preterm until they are 3 years old. 

The CDC has created a training module for using the CDC growth tools.     

• Often percentile and z score calculations are incorporated into the electronic health record and, typically, no decision about what chart to use is required. 
• If using paper charts 
  • The 2000 CDC BMI-for-age growth charts should be used for boys and girls 2 years and older who are at or below the 95th percentile. 
  • Use extended BMI-for-age growth charts for children whose BMI is above the 95th percentile.