Poor weight gain is the finding of weight loss or a deceleration in the rate of weight gain. Failure to thrive describes the condition of infants and toddlers under age 2 years who have an abnormally low weight relative to their stature for their age and sex. With prolonged and/or severe malnutrition, linear growth and head circumference can be secondarily affected. The term failure to thrive is not a singular disorder; rather, poor growth is a sign of an underlying problem that leads to insufficient usable nutrition. A wide variety of medical and psychosocial factors can contribute to poor weight gain.
The prevalence of failure to thrive is reported to be 5% to 10% in primary care settings. Community studies indicate that up to 50% of children with failure to thrive are not identified. Recurrent failure to thrive is reported in 5% of children due to diarrhea, respiratory infections, urinary tract infections, discontinuation of breastfeeding, teething, and age of initiating complementary feeding. Regardless of specific etiology, failure to thrive may have profound effects on the growing child, including persistent short stature, decreased resistance to infection, and developmental impairment and/or disabilities.
Failure to thrive is characterized by insufficient growth recognized by the observation of growth over time using standard growth curves for age and gender. This condition is also called weight faltering or growth failure. There is a lack of consensus regarding the specific anthropometric criteria required to classify failure to thrive. Thus, many “definitions” for failure to thrive are commonly used in children under 2 years of age. These include weight less than 3rd percentile for corrected gestational age, weight-for-length less than 5th percentile, or downward crossing of 2 or more major percentiles on the growth chart. Other definitions include weight less than 80th percentile of ideal weight-for-age, triceps skinfold thickness of 5 mm or less, or a depressed rate of weight gain compared to that expected for age and gender. The interpretation of failure to thrive based on the pattern of height and weight from growth charts may be misleading because 25% of children demonstrate normal growth rate shifts during infancy and early childhood. Hence, a fall in growth velocity that persists is key and accuracy in obtaining and plotting growth measurements is implicit to the diagnosis. Special growth charts for prematurity and selected genetic syndromes should be used when indicated.
Three basic mechanisms underlie poor weight gain: (1) inadequate nutrient intake, (2) insufficient utilization or impaired absorption of consumed nutrition, and (3) increased metabolic requirements. There are numerous specific etiologies for failure to thrive (see Table 22-1). However, most commonly, it results from insufficient intake of dietary energy and nutrients due to lack of food offered, chewing and swallowing dysfunction, and/or behavioral problems that limit a young child’s intake. In many cases, a specific organic etiology ...