Failure to thrive (FTT) is an older term, now more often called growth faltering or faltering weight in children. It means a child is not gaining weight, length, or BMI as expected for age because nutritional needs are not being met or because of an underlying medical, feeding, developmental, or psychosocial problem.

Common categories:

Assessment centers on serial growth measurements and z-scores, a detailed feeding history, physical examination, development, and family/social context. Broad blood tests or imaging are usually not first-line unless there are concerning symptoms, severe malnutrition, or no response to nutritional intervention. The AAP's 2026 summary uses criteria such as low weight-for-length/BMI-for-age or a significant decline in weight z-score.

Seek urgent pediatric assessment if there is dehydration, lethargy, persistent vomiting, blood in stool, breathing difficulty, recurrent serious infections, developmental regression, suspected neglect, or rapid weight loss.

Most cases can be managed outpatient with targeted feeding support, calorie optimization, close weight follow-up, and treatment of the cause; hospitalization is generally reserved for severe or refractory cases. Swanson's Family Medicine Review, p. 559. The AAFP clinical review provides a practical evaluation and management overview.