WHO vs. CDC growth charts

Two sets of growth charts are commonly used in the US:

WHO charts (0–2 years): based on children raised under ideal conditions (breastfed, non-smoking households, regular medical care) across six countries. Considered a prescriptive standard - how children should grow.
CDC charts (2–20 years): based on US children from multiple national surveys. Descriptive - how US children actually grow, which includes higher rates of overweight.

Interpreting percentiles

Percentile range	Clinical interpretation
3rd–97th	Normal range; most healthy children fall here
Below 3rd	Short stature; warrants monitoring and possible evaluation
Above 97th	Tall stature or overweight; context-dependent
Trend crossing 2+ bands	More clinically significant than any single percentile value

Head circumference

Head circumference is routinely measured through age 2–3 to track brain growth. A head circumference below the 2nd percentile (microcephaly) or above the 98th percentile (macrocephaly) may indicate a neurological condition and warrants evaluation. Head circumference is not routinely used as a standalone diagnostic - trends over time and relationship to weight and height percentiles are more informative.

Failure to thrive

"Failure to thrive" (FTT) is a clinical concern - not a diagnosis - typically triggered when a child's weight drops across two or more major percentile bands (e.g., from 50th to below 25th), falls below the 3rd percentile, or weight-for-length falls below the 5th percentile. Causes are medical, nutritional, or psychosocial; evaluation requires clinical assessment beyond any growth chart tool.