Failure to thrive in infants and children

José M Moreno-Villares MD

Antonio Monica Guerra MD

Introduction

Evaluation of growth and development in the primary care setting is a cornerstone of paediatric care. Usually head circumference, weight, and length are measured at birth, and then on an intermittent basis throughout the rest of childhood. When a divergence from the standard growth curve occurs, in either direction, a careful assessment is required to determine the aetiology.

Undernutrition or ‘failure to thrive’ (FTT) is a common nutritional problem in the infant and toddler paediatric population. The identification of patients with FTT is a routine part of residency training in paediatrics.

Inappropriate nutrient intake and growth parameters

FTT is a clinical label frequently used to describe infants and young children, generally under 3 years, who fail to grow as expected using established growth standards for age and gender along a period of time (usually longer than 3 months) (1.1).

Weight is a measure of the varying combination of height, body fat, and muscle bulk, which makes it a less straightforward measure of growth than height. Nevertheless, because of its widespread availability and ease of measurement, it is the most usual tool when growth measure is considered. What constitutes a normal rate of weight gain (Table 1.1)? It is often assumed that normal growth constitutes tracking along the birth centile. However, weight at birth is a reflection of the intrauterine environment and is of limited prognostic value. Many children deviate from their earlier centile position, and this divergence may not become pathological. Although the most commonly used definition of abnormality is that falling below a predetermined centile, usually the third (1.2), this would include a number of constitutionally small children. An alternative definition applies when a child has a weight curve that has fallen more than two standard deviations or
percentiles below a previously established rate of growth. However, up to 30% of healthy term infants cross one percentile line and 23% cross two percentile lines (in either direction) by the age of 2 years.

1.1 Eleven-month-old male, with growth faltering in the last 4-5 months, more severe in the last 2 weeks. Reduction in >2 major percentiles for weight.

Table 1.1 Normal weight gain and frequency of monitoring

Normal weight gain
Birth to 5 months	15-30 g/day
6 to 12 months	15 g/day
12 months to 2 years	6-8 g/day
2 years to 6 years	38 g/month

Frequency of monitoring
Monthly for the first two months, every other month from 2 to 6 months; every 3rd month from 6 to 24 months, and yearly from 2 to 6 years old

1.2 An 18-week-old female, with irritability and poor weight gain since birth. Weight below 3rd percentile.

Definition of FTT

FTT describes an infant or child whose current weight or rate of weight gain is significantly below that expected of similar children of the same age and sex. Most paediatricians diagnose FTT when a child’s weight for age falls below the fifth percentile of the standard growth charts or it crosses two major percentile lines (1.3). One problem arises from the use of different growth charts; misinterpretation may occur if different genetic backgrounds are not considered. This problem may be overcome if universal growth references could be used. The World Health Organization (WHO) has recently published charts resulting from the Multicenter Growth Reference Study, and are intended to substitute for the National Center for Health Statistics/WHO (NCHS/WHO) growth reference, which has been recommended for international use since the late 1970s (www.who.int/childgrowth/standards/curvas_por_indicador es/en/index.html) (1.4, 1.5).

FTT is not a final diagnosis but a description of a physical state; therefore, a cause must always be sought. Because the description itself is vague it has been proposed to use growth failure or undernutrition as a diagnostic replacement for FTT.

1.3 Four-month-old male. Loss of >2 major percentiles since birth.

1.4 WHO growth curves. Height/length for age (boys).

Until recently, the evaluation of a child with FTT focused on factors related to external environment or to medical causes. Currently, the child’s feeding behaviour and the interaction between the caregiver and the child has taken on greater importance. Feeding is an interactive process that depends upon abilities and characteristics of both the parents and the child.

Aetiology

FTT has been historically dichotomized as organic versus nonorganic (1.6). Organic FTT results from a major organ system illness or dysfunction, while nonorganic FTT is generally a diagnosis of exclusion. A third category has been added, mixed FTT, to recognize the fact that many organic FTT often have a psychological component. This approach is quite simplistic and inadequate for patient management. There is growing evidence that feeding difficulties are central to the development of the disorder. Family stressors, psychiatric disorders of parents, and disturbances in the infant-parent relationship may interfere with the development of an adequate feeding relationship.

1.5 WHO growth charts. Length/height for age (girls).

1.6 Aetiology of FTT.

It is important to note that an infant presenting with presumed FTT may have a normal variant of growth¹. Specific infant populations with growth variations also need to be considered when making the diagnosis of FTT, for instance, infants with intrauterine growth retardation or premature infants.

Table 1.2 Normal variants of growth presenting as FTT

	Genetic short stature	Ex-premature infant	Constitutional delay	Catch down growth
Birth weight	Low to normal	Normal if corrected for gestation	Low to normal	Above expected for genetic background
Parental percentiles	Low	Normal	Normal	Normal
Progress along percentiles	Low percentile but do not cross percentiles	Low if corrected but follow percentile curves	May be an initial fall in first 6 months and then follow percentiles	Initial fall in 6-12 months and then follow percentiles

Table 1.3. Classification of FTT by pathological causes

Inadequate caloric intake
•	Food not available
–	Type or volume of food not appropriate (e.g. too diluted formula)
–	Poverty and food shortages
–	Neglect
–	Feeding technique, parent-infant interaction problems
•	Lack of appetite
–	Chronic illness
–	Psychosocial disorder
•	Mechanical feeding difficulties, e.g. oral-motor dysfunction or malformation
Reduced absorption or digestion of nutrients
•	Pancreatic insufficiency: cystic fibrosis
•	Loss or damage to villous surface
–	Coeliac disease
–	Cow’s milk protein allergy
–	Vitamin or mineral deficiencies
•	Cholestasis
Excessive loss of nutrients
•	Vomiting
–	Gastro-oesophageal reflux
–	Other causes of vomiting: central nervous system disorders, metabolic disease
•	Malabsorption/diarrhoea
–	Inflammatory bowel disease
–	Short bowel syndrome
•	Renal losses
–	Renal failure or tubular acidosis
–	Diabetes mellitus or diabetes insipidus
Defective utilization
•	Chromosomal or genetic abnormality
•	Metabolic disorder
•	Endocrine disorder
•	Congenital infections
Increased metabolism
•	Chronic infection or inflammation
•	Hypoxaemia (congenital heart disease, chronic lung disease)
•	Hyperthyroidism
•	Malignancy