When is it appropriate to use the WHO BMI‑for‑age reference for assessing nutritional status in children and adolescents aged 2 to 19 years?

When to Use WHO BMI-for-Age Growth Charts in Pediatric Practice

Use WHO BMI-for-age charts for children from birth to 24 months of age, then transition to CDC growth charts for children aged 2 to 19 years. 1, 2

Age-Specific Chart Selection

Birth to 24 Months: WHO Growth Standards

• WHO growth charts are the recommended standard for all infants and toddlers under 24 months, regardless of feeding method (breastfed or formula-fed). 1, 3
• The WHO charts are based on data from healthy, predominantly breastfed infants from multiple countries, representing optimal growth conditions rather than simply describing how children grew in one population. 1
• WHO BMI-for-age charts begin at birth, providing continuous assessment from the neonatal period forward. 1
• These charts use the 2.3rd and 97.7th percentiles (±2 standard deviations) as clinical thresholds for identifying potential adverse health conditions, rather than the traditional 5th and 95th percentiles. 1

24 Months to 19 Years: CDC Growth Charts

• After age 24 months, switch to CDC growth charts, which extend continuously through age 19 years. 1, 2, 3
• The CDC charts provide age- and sex-specific BMI percentiles (5th, 10th, 25th, 50th, 75th, 85th, 90th, 95th) for nutritional status classification. 1
• For children aged 2-19 years, overweight is defined as BMI between the 85th and 94th percentile, and obesity as BMI ≥95th percentile. 1, 2
• Severe obesity is defined as BMI ≥120% of the 95th percentile or absolute BMI ≥35 kg/m², whichever is lower. 1, 2

Clinical Rationale for the Transition at 24 Months

Why WHO Charts for Infants

• Breastfeeding is the recommended standard for infant feeding, and WHO charts are specifically designed with breastfed infants as the reference population (100% breastfed for 12 months, predominantly breastfed for ≥4 months). 1
• Breastfed infants gain weight faster than formula-fed infants during the first 2-3 months, then gain more slowly from approximately 3 months onward—a normal physiologic pattern that WHO charts accurately reflect. 3
• Using CDC charts for infants under 24 months incorrectly identifies more children as underweight, because CDC charts are based on a mixed-feeding population with higher rates of formula feeding. 1, 3

Why CDC Charts After 24 Months

• CDC charts provide continuity through adolescence with a single reference system, avoiding multiple transitions. 1, 3
• The CDC reference includes a broader, more representative U.S. population sample for older children and adolescents. 1
• At 24 months, there is a smooth transition between WHO and CDC charts with minimal disjunction in percentile classification. 1

Special Populations Requiring Different Approaches

Preterm Infants

• Very low birth weight infants (<1.5 kg) should not be plotted on standard WHO or CDC charts. 3
• Use prematurity-specific growth curves (e.g., Fenton, INTERGROWTH-21st) until corrected gestational age reaches term-equivalent. 3
• Correct for gestational age until 24 months of chronological age when plotting measurements. 3

Children with Chronic Kidney Disease

• WHO growth standards are recommended for children with CKD from birth to 2 years. 1
• These charts help identify growth faltering early, which is common in pediatric CKD and requires aggressive nutritional intervention. 1

Ethnically Diverse Populations

• BMI alone may underestimate adiposity in South Asian children due to lower lean body mass at a given weight. 1, 2
• Consider waist circumference as an adjunct measure in populations with known ethnic variations in body composition, though measurement reliability decreases in severe obesity. 1, 2
• When country-specific growth data are available, they may be more appropriate than international references for certain populations. 4, 5

Key Clinical Thresholds and Their Interpretation

Undernutrition Screening

• Values below the 2.3rd percentile (2 SD below median) warrant evaluation for underlying causes including chronic malnutrition, malabsorption, or medical conditions. 1, 3
• A drop of 40 percentile points (e.g., 50th to 10th percentile) represents clinically significant growth faltering requiring immediate intervention, even if the child remains above the 2.3rd percentile. 3

Overweight and Obesity Classification

• 85th-94th percentile = overweight; ≥95th percentile = obesity; ≥99th percentile or ≥120% of 95th percentile = severe obesity. 1, 2
• At age 19 years, the WHO BMI-for-age +1 SD corresponds to BMI 25 kg/m² (adult overweight threshold) and +2 SD corresponds to BMI 30 kg/m² (adult obesity threshold), ensuring smooth transition to adult classifications. 6

Common Pitfalls to Avoid

Measurement and Plotting Errors

• Do not use WHO charts for children older than 24 months—this leads to misclassification because the reference populations and statistical methods differ. 1, 3
• Do not use CDC charts for infants under 24 months—this overdiagnoses underweight and can damage parent-child feeding interactions through unnecessary medical interventions. 1, 3
• Ensure accurate measurement technique: recumbent length for children <24 months, standing height for ≥24 months; the difference between length and height measurements is approximately 0.5-1.0 cm. 3

Interpretation Errors

• Do not rely on a single measurement—growth velocity over time (serial measurements every 1-3 months for infants, every 3-6 months for older children) is far more informative than isolated percentile position. 2, 3
• Do not assume that lower percentiles indicate pathology—consistent tracking along any percentile curve (even the 3rd percentile) represents normal constitutional growth if the child maintains their trajectory. 3
• Do not ignore family growth patterns—calculate mid-parental height to determine if a child's percentile reflects genetic potential. 3, 7

Clinical Decision Errors

• Do not initiate formula supplementation for breastfed infants showing normal WHO chart patterns without first assessing lactation adequacy and breastfeeding technique. 3
• Do not pursue extensive metabolic work-up before confirming adequate caloric intake and documenting response to nutritional optimization over 2-4 weeks. 3
• Do not use absolute BMI values (adult cut-offs) for children under 18 years—age- and sex-specific percentiles are required because BMI changes normally during growth. 1, 2