Definition of Failure to Thrive
Failure to thrive (FTT) is growth retardation without a known cause in infants and young children, characterized by inadequate weight gain that falls below the 3rd-5th percentile or crosses two major percentile lines downward on growth charts. 1, 2
Core Anthropometric Criteria
The diagnosis relies solely on anthropometric parameters, with weight being the predominant indicator: 3
- Weight below the 3rd-5th percentile on standardized growth charts 4, 2, 5
- Weight deceleration crossing two major percentile lines downward 2
- Disproportionate growth pattern where weight is affected first while height and head circumference remain relatively preserved, indicating acute malnutrition 4
Time-Based Diagnostic Thresholds
The duration of inadequate growth required for diagnosis varies by age:
Infants (Under 12 Months)
- Persistent inadequate weight gain for more than 3 months warrants diagnosis and intervention 4
- The 3-month timeframe is critical because early infancy is especially sensitive to growth-suppressing influences 4
Children and Adolescents (Over 12 Months)
- Persistent growth failure lasting more than 6 months combined with height velocity below the 25th percentile and height below the 3rd percentile 4
Updated Terminology
The preferred contemporary term is "growth faltering" rather than "failure to thrive," though this can be ambiguous in populations with inherently low height growth (such as skeletal dysplasias). 1 Despite terminology debates, FTT has maintained its own ICD-9 code since 1979. 6
Underlying Pathophysiology
FTT results from one of three mechanisms: 7, 2
- Inadequate caloric intake (difficulties with nursing, limited food availability, incorrect formula preparation, oral aversion)
- Inadequate caloric absorption (metabolic, gastrointestinal, or pancreatic disorders)
- Excessive caloric expenditure or ineffective utilization (hyperthyroidism, diabetes, cardiac or pulmonary conditions)
Clinical Context
Most cases in the United States (5-10% of children in primary care) involve inadequate caloric intake from behavioral or psychosocial issues rather than organic disease. 2 However, organic causes must be systematically excluded, particularly when specific symptoms like vomiting, feeding irritability, or respiratory distress accompany the growth failure. 4, 8
Critical caveat: Using any single anthropometric indicator has low positive predictive value, so diagnosis should incorporate multiple measurements over time plotted on WHO growth charts (birth to 2 years) or CDC charts (age 2 years and older). 4, 7