Transitioning from WHO to CDC Growth Charts at 2 Years of Age
When a child reaches age 24 months, health care providers need to switch from using the WHO growth standards charts to using the CDC growth reference charts for children ages 2 years up through 19 years. During the transition from one chart to another, children may experience a difference in classification because of a change from:
- Recumbent length to standing height measurements. Note that the difference between recumbent length and stature in national survey data is approximately a 0.8 cm (¼ inch) difference. Standing height measures less than recumbent length.
- 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.
WHO Weight-for-Length Chart to the CDC BMI-for-Age Chart
Moving from the WHO weight-for-length chart to the CDC BMI-for-age chart may result in a change in a child’s percentile classification because of
- Changes from one indicator to another indicator.
- Changes from a recumbent length measurement to a standing height measurement.
- Changes to a different cutoff value and a different reference population.
A child who is identified as being 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 25th and 50th 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 10th percentile. Both percentile classifications are within the healthy range.
WHO Length-for-Age Chart Compared to the CDC Length-for-Age Chart
- In general, the WHO and the CDC length-for-age growth charts are somewhat similar.
WHO Weight-for-Age Chart Compared to the CDC Weight-for-Age Chart
- 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 at 2 years of age, the weight-for-age percentiles may change downward to a lower percentile.
For example, a weight of 26 ¾ 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.
During this transition, caution should be used in interpreting any changes.
- Growth measurements need to be used in conjunction with medical and family history if aberrant growth is identified.
Growth monitoring is based on a series of measurements.
- When assessing physical growth, it is critical to have a series of accurate measurements to establish an observed growth pattern.
- A series of accurate measurements takes into consideration short- and long-term conditions and provides a context for individual measurements in interpretation. Thus, misinterpretation can be avoided based on a single plot on a different chart.