Failure to thrive true Faltering weight Weight faltering Postnatal failure to thrive Although there is no clear consensus on the exact definition of FTT, it is usually diagnoses in a child growing below the 3rd percentile or in a child whose decreased growth has cross two major growth percentiles (for example, from above the 75th percentile to below the 25th percentile). SNOMEDCT_US:36440009 HP:0001535 HP:0001508 Undergrowth Poor weight gain UMLS:C0231246 Failure to thrive (FTT) refers to a child whose physical growth is substantially below the norm. UMLS:C2315100 HP:0008916 SNOMEDCT_US:432788009 HP:0008878 HP:0008853 FTT Decreased body weight