Using WHO Growth Standard Charts

Online access to growth charts

CDC recommends using WHO Child Growth Standards in U.S. clinical settings for children from birth to 2 years. They are scaled for both English and metric measurements. For children from birth to 2 years, the WHO charts include:

• Boys' weight-for-length percentiles and head circumference-for-age percentiles.
• Boys' length-for-age percentiles and weight-for-age percentiles.
• Girls' weight-for-length percentiles and head circumference-for-age percentiles.
• Girls' length-for-age percentiles and weight-for-age percentiles.

The WHO Child Growth Standards include a body mass index (BMI) chart beginning at birth. However, the BMI-for-age growth chart is not recommended for children younger than 2 years. BMI in infancy is based on recumbent length (measured lying down) rather than stature. There is little research on what BMI calculated from length means in infancy, or its consequences.

Assessing growth

Accurate measurements and recording of information is critical for growth charts to be an effective screening tool. To assess growth for children younger than 2 years using WHO Child Growth Standards:

• Use recommended protocols to measure the weight and recumbent length of the child.
• Record the measurements correctly.
• Calculate age correctly.
• Plot measurements on the appropriate WHO Growth Chart. Use the percentile lines to:
  • Assess body size and growth.
  • Monitor growth over time.

Percentile cutoff values

WHO recommends cutoff values of +2 standard deviations to define abnormal growth.^[1] These cutoff values correspond to the 2.3rd and 97.7th percentiles. On the WHO Child Growth Standards, these cutoff values are labeled as the 2nd percentile and the 98th percentile. For children younger than 2 years:

• Low weight-for-length: weight-for-length that is less than the 2nd percentile for age and sex.
• High weight-for-length: weight-for-length that is higher than the 98th percentile for age and sex.
• Short stature: length-for-age that is less than the 2nd percentile.

Infant growth patterns

Growth patterns differ between breastfed and formula-fed infants. Beginning around 3 months of age, weight gain is generally lower for breastfed infants than for formula-fed infants.^{[6, 7, 13]} Linear growth generally follows a similar pattern for both breast- and formula-fed infants.^[9]

For the first 3 months of age, the WHO growth charts show a somewhat faster rate of weight gain than the CDC growth charts.

After about 3 months of age, WHO growth charts show a slower rate of growth than the CDC growth charts. Because formula-fed infants tend to gain weight more rapidly after age 3 months, they may be more likely to cross upward in percentiles on the WHO growth charts, perhaps becoming classified as high weight for length.^[5]

Transitioning from WHO to CDC growth charts

When a child reaches 2 years of age (24 months), health care providers should switch from using the WHO Child Growth Standards charts to using the CDC Growth Reference charts (also called CDC growth charts). CDC growth charts are recommended for children and adolescents 2 to 20 years.

Classification

During the transition from one chart to another, children may have a different classification because of a change from:

• Recumbent length to standing height measurements. Standing height measures less than recumbent length (about 0.8 cm or ¼ inch), according to national survey data.
• Breastfed reference population to a primarily formula-fed reference population.
• Weight-for-length chart to BMI-for-age chart.
• One set of cutoff values to another.

Weight-for-length

Moving from the WHO weight-for-length chart to the CDC BMI-for-age chart may change the child's percentile classification because of changes:

• From one indicator to another indicator.
• From a recumbent length measurement to a standing height measurement.
• To a different cutoff value and a different reference population.

A child at a specific percentile when plotted on the WHO weight-for-length chart may "drop" to a lower percentile on the CDC BMI-for-age chart. For example, a 24-month-old boy weighing 24 pounds and 4 ounces with a length of 23.25 inches is plotted between the 25^th and 50^th percentiles on the WHO weight-for-length chart. When plotted on the CDC BMI-for-age chart, the same boy is plotted just above the 10^th percentile. Both percentile classifications are within the healthy range.

Length-for-age

In general, the WHO and the CDC length-for-age growth charts are similar.

Weight-for-age

The WHO weight-for-age charts show a pattern of slower weight gain after about 3 months of age since they are based on the weights of breastfed infants. When changing from the WHO-weight-for-age chart to the CDC weight-for-age chart, the weight-for-age percentiles may change to a lower percentile.

For example, a weight of 26¾ pounds for a 24-month old boy is at about the 50th percentile on the WHO weight-for-age chart. The same weight on the CDC weight-for-age chart is between the 25th and the 50th percentile. Both percentile classifications are within the healthy range.

Interpret changes with caution

During this transition, health care providers or other users of growth charts should interpret any changes in a child's percentile classification with caution. Growth measurements can be used in conjunction with medical and family history if abnormal growth is identified.

Growth monitoring is based on a series of accurate measurements over time. This series of measurements accounts for both short- and long-term conditions and provides context for interpreting an individual measurement.

Test your knowledge

1. High weight-for-length is defined as weight-for-length that is higher than the 75th percentile for age and sex.
   1. True
   2. False
2. Health care providers should exercise caution when transitioning from the WHO to CDC growth charts, which occurs at 2 years of age.
   1. True
   2. False

See answers.A