When a Child is Considered Failure to Thrive
A child is diagnosed with failure to thrive when their weight falls below the 3rd percentile OR when weight crosses down two major percentile lines on a growth chart, particularly when this occurs in the first 1-2 years of life. 1, 2, 3
Primary Diagnostic Criteria
Weight-Based Definitions
- Weight below the 5th percentile on multiple occasions is the most commonly used threshold, though this has lower specificity 3, 4
- Weight below the 3rd percentile is a more specific criterion and indicates clinically significant growth failure 5, 2
- Weight deceleration crossing two major percentile lines on WHO (birth to 2 years) or CDC growth charts (after age 2) represents dynamic growth failure 6, 3
Growth Pattern Recognition
- Weight is affected disproportionately before height and head circumference - this is the hallmark pattern distinguishing acute malnutrition from genetic short stature 5, 2
- A child with weight at 3rd percentile but height and head circumference at 25th percentile demonstrates the classic acute malnutrition pattern of FTT 5
Time Course for Diagnosis
Infants (Under 12 Months)
- Persistent growth failure beyond 3 months of inadequate weight gain warrants diagnosis and intervention 7, 5
- This shorter timeframe reflects the critical sensitivity of infancy to growth-suppressing effects 7
Children and Adolescents (Over 12 Months)
- Persistent growth failure beyond 6 months with height velocity below the 25th percentile and height below the 3rd percentile indicates FTT requiring intervention 7
Important Clinical Context
Terminology Evolution
- The preferred modern term is "growth faltering" rather than "failure to thrive," though both remain in clinical use 1
- FTT represents a state of undernutrition from inadequate caloric intake, absorption, or excessive expenditure 2, 6, 3
Prevalence and Presentation
- FTT affects 5-10% of children seen in outpatient primary care settings 2, 8, 3
- Most commonly recognized in the first 1-2 years of life but can present at any age in childhood 2
Critical Pitfall
No single anthropometric criterion is sufficiently sensitive - using multiple criteria together (weight percentile, rate of weight gain, and pattern of growth across parameters) provides the most accurate identification of growth faltering 8, 3. Relying solely on a single measurement or percentile cutoff will miss many cases or create false positives.