If you've ever looked at growth charts online, you've probably seen two different standards: WHO (World Health Organization) and CDC (Centers for Disease Control). They look similar, but they tell different stories — and for young children, using the wrong one can lead to misinterpretation.
The Core Difference
The fundamental difference is what each chart represents:
| Feature | WHO (2006 / 2007) | CDC (2000) |
|---|---|---|
| Type | Prescriptive standard | Reference data |
| Question asked | "How should children grow?" | "How did US children grow?" |
| Study design | Optimal conditions (breastfed, non-smoking, etc.) | Mixed US population |
| Age range | 0–5 years (2006) + 5–19 (2007) | 0–20 years |
| Recommended for <2 years | ✅ Yes | ❌ No |
Why WHO is the Global Standard for Under 2
The WHO charts were built from the MGRS (Multicentre Growth Reference Study) — a landmark study across 6 countries (Brazil, Ghana, India, Norway, Oman, USA) that tracked healthy children raised under optimal conditions: exclusively breastfed for 6 months, non-smoking households, no significant socioeconomic barriers to growth.
This is prescriptive — it shows how children should grow when given optimal conditions, making it the correct yardstick regardless of population. The CDC charts, by contrast, are descriptive — they show how American children actually grew in the 1990s, including formula-fed and overweight children, which inflates expected weights in early infancy.
Practical Impact: Real Example
A breastfed infant who appears to drop from the 25th to the 10th percentile on the CDC chart (causing concern) may actually be tracking perfectly on the WHO chart. This is because formula-fed infants gain weight faster in early infancy, inflating the CDC reference curves — making breastfed babies look like they're lagging when they're not.
Use WHO if:
- Your child is under 2 years
- You are outside the US
- Your child is breastfed
- You want a global standard
Use CDC if:
- Your child is 2–20 years (US)
- Your US paediatrician uses it
- Comparing to US population data
What GrowChart Uses
GrowChart uses the WHO Child Growth Standards for all ages (0–19 years), which is the internationally recommended standard used by paediatricians, WHO-affiliated clinics, and UNICEF worldwide. Our LMS-based z-score engine matches the official WHO software output exactly.