The three measures
of body size shown on the growth charts for infants (birth to 36 months
of age) are length, weight, and weight relative to length. The latter
is an indicator of how the child's weight matches his or her length. Weight-for-length
corresponds to body-mass-index-for-age in older children.
In children less than 2 years old, recumbent length is measured; in children over 3 years old, stature (height) is measured. For children between 2 and 3 years old, there is a choice. Either length or stature can be measured. To continue to use the set of charts for birth to 36 months, measure length; to use the charts for 2 to 20 years, including the BMI-for-age chart, measure stature.
CDC recommends using the BMI-for-age charts beginning at age 2 years because BMI-for-age can be used to track overweight into adulthood. On the other hand, for children between 2 and 3 years, the charts for birth to 36 month charts offer continuity with their earlier data and show data in a more expanded display that is easier to interpret.
In this module we use the charts of infants and children from birth to 36 months. These charts include weight-for-age, length-for-age, head-circumference-for-age, and weight-for-length. (The use of head circumference-for-age is reviewed in the module, Interpreting Growth in Head Circumference.)