Failure to Thrive

Normal Growth

Newborns typically lose up to 10–12% of their birthweight during the first few days of life and regain this weight by the age of 2 weeks. Subsequently, they gain weight at a steady pace of about 1 ounce per day for the first 2 or 3 months; they gain at half to two thirds that rate for the next 3 months and half to two thirds again for the next 6 months. This results in a doubling of birthweight by the age of 4–6 months and a tripling at about 1 year. Height and head circumference grow at similar well-defined rates. These three growth parameters, along with weight/length, should be plotted on appropriate growth charts and monitored for adherence to standard growth rates. Children grow in a stepwise manner, but on average their growth pattern follows the accepted curves (see Chapter 56 ). Online tools are available to assist with the determination of growth status ( http://peditools.org ).

By the age of 3 years, if caloric intake is normal, the child’s growth adjusts to their genetic potential. Ultimate height is determined by additional factors, among them rates of bone maturity and pubertal development (see Chapter 56 ). Considerable energy from ingested food is required to achieve this growth. The energy balance can be described by the following equation, in which E equals energy:

E _OUT is the sum of the basal metabolic rate, energy expended in physical activity, and energy needed for food digestion. Children should be in a positive energy balance for growth. Any imbalance in this energy equation (losing or using more calories than are ingested) results in abnormal growth patterns. Weight is usually affected first, followed by height and finally head circumference if the energy imbalance is severe and prolonged in young children.

Definitions

FTT is a sign, not a diagnosis. FTT is generally used to describe children younger than 2 or 3 years who meet any of the following criteria:

• 1.

  Growth under the third percentile on World Health Organization (WHO) weight-for-age growth charts (less than 2 standard deviations [SD] below mean)

• 2.

  Weight for height or body mass index (BMI) less than the third percentile

• 3.

  Growth patterns that have crossed two major percentiles downward on the weight-for-age charts within 6 months

• 4.

  Growth velocity less than normal for age

There are inherent problems with these definitions. Two percent of the normal population is under 2 SD below the mean; those who are growing appropriately per their genetic potential must be differentiated from those with growth problems. The child who has been obese and is now approaching normal weight, crossing major weight percentiles in the process, should not be considered a child with FTT. Some children are naturally slim. The clinician must exercise considerable judgment before raising the concern of poor growth.

Additional terms are used to describe children who are not growing well. A child has wasting if the weight for length (or height) is below –2 SD (or −2 z-scores, which is equal to <2nd centile). Stunting is defined as a child whose height or length is less than −2 z-scores due to chronic undernutrition. In the third year of life, children are described as underweight if weight/age is <3% or if BMI is <5%. Short stature or microcephaly alone is not due to nutritional deficiencies ( Table 12.1 ).

Interpretation of Growth Charts

The evaluation for any child who is not growing well includes a careful analysis of the growth pattern over time. Measurements of length are the most susceptible to error; standard procedures should be used (see Chapter 56 ). Possible errors in weight, head circumference, date of birth, or plotting on the growth chart should all be considered. Once the correct data are available, the charts should be examined to answer the following questions:

• Are the measurements of length and weight proportional?

• Has the head grown adequately?

• How severe are the deficits of each measurement, relative to what is expected?

• When did the problem start; what is the progression?

• What environmental factors were present at the start of this process (weaning, introduction of new foods, food insecurity)?

Although weight is usually the most readily available measurement, measurement of length is particularly critical, because it serves as the point of reference for other diagnostic considerations. The best way to obtain accurate length measurements is to use a specially calibrated length board with a fixed headpiece and a movable footpiece. In the absence of such a device, the examiner can use a table or desk with the infant’s head pressed against the wall and a firm square box or thick textbook for the sliding footer. Measurements obtained with the infant lying on a mattress and marked with a pen on the sheet are not accurate (see Chapter 56 ).

The choice of growth curves is important. In the United States, the recommendation is to use the WHO charts from birth through the second year of life ( http://www.cdc.gov/growthcharts/who_charts.htm ) (see Chapter 56 ). Some children previously classified as FTT will fall into the normal range. Their health status may be poorer than those within normal ranges on both charts. The 2000 age- and gender-specific National Center for Health Statistics growth charts published by the Centers for Disease Control and Prevention combined data across geographic and ethnic populations and are appropriate to use for children over 24 months of age.

Conventions (for premature infants) differ in whether to plot age in relation to actual birth date or to use corrected gestational age. Growth charts following children prenatally to infancy are available (see Fenton and Olsen at http://peditools.org ). Beyond the equivalent of 40 weeks of gestation, standard charts can be used, keeping in mind that premature infants may not catch up on all parameters for 2 or 3 years.

Because infants with FTT no longer follow their growth curves, the usual convention of expressing growth measurements in relation to normal percentiles is not always useful; weight/length or BMI z-scores better define and assess the degree of malnutrition. Children with moderate wasting have weight for height below −2 SD of the WHO Child Growth Standards median; severe wasting is defined as weight for height below −3 SD.

It is important to note the following points:

• 1.

  Infants and toddlers who are short in proportion to weight should be considered to have primary growth problems, including various endocrine (often growth hormone) and skeletal dysplasias (see Chapter 56 ) (see Table 12.1 ).

• 2.

  Infants who have had inadequate caloric intake will be abnormally thin. If the problem developed at some time after birth, weight will drop off before changes in length or head circumference.

• 3.

  Infants with disproportionately small heads may have primary neurologic or genetic (monogenetic, microdeletion, aneuploidy, syndromic) problems affecting brain growth because head growth is the last to be affected by malnutrition and is not characteristic of primary skeletal growth problems (see Table 12.1 ). An alternative diagnosis is craniosynostosis, or early closure of skull growth plates.

Several examples of how these patterns may be interpreted are presented in Figures 12.1 to 12.4 . Growth charts adjusted for abnormal head size (micro- or macrocephaly) are not available. This factor becomes relatively less important as the child ages, but during infancy it may significantly affect the weight percentile and requires clinical judgment to assess.

Syndrome-specific growth charts have been developed for certain populations (e.g., trisomy 21, skeletal dysplasias). Their use is most appropriate for conditions that affect muscle and bone development (e.g., Russell-Silver syndrome). All other disease-specific charts should be used in conjunction with the WHO charts. Accuracy of some of these charts is suspect.

Epidemiology

FTT is found in all populations but has a higher prevalence among children of low socioeconomic status compared to those in higher socioeconomic groups. FTT accounts for up to 5% of all hospitalizations; up to 10% of children may have FTT at some point in time. Most affected children with nutritional problems present before the age of 3 years.

Clinical Presentation

Parents often voice concerns about their young child’s weight gain. They may complain that their child is a picky eater or seems not to drink enough formula, or they worry that breast milk supply is inadequate. Very commonly, parents complain that their child is not as big as a similar-aged child or a sibling at that age. Many such children are growing normally. Plotting the child’s growth and reviewing it with the parents may be reassuring, or it may serve to confirm the parents’ concerns. When families raise concerns about growth, regardless of whether a problem exists, the child and the weight have already become a focus of concern for that family. Often parents have already put a great deal of effort into changing the child’s eating patterns, leading to intrafamily conflict. In this setting, conversations about the child’s growth may carry a high emotional charge.

However, it is often the physician who is first to raise concerns. These suspicions can be confirmed by carefully plotting the growth parameters. The clinician must then prioritize the clinical issues and decide whether the FTT should be addressed immediately or deferred for evaluation and management at another time in the very near future. In rare cases, the growth failure is so severe that immediate hospitalization is indicated for nutritional rehabilitation. In this case, the evaluation can take place over several days, while therapeutic nutritional interventions are ongoing.

Approach to Determining Etiology

Clinicians need to have a broad approach to determining etiology of FTT for each child. Many children with FTT, particularly those with chronic diseases, have a mixed pattern of increased needs or losses attributable to organic causes, along with environmental causes leading to calorie deprivation.

There are several growth conditions that result in smaller than normal size that are not due to calorie insufficiency. Infants who are born symmetrically small in all growth parameters are believed to have a reduced number of somatic cells in relation to their normal-sized peers as a result of an early intrauterine event. Infants who are asymmetrically small for gestational age, with sparing of the head circumference and possibly length, had a late intrauterine event, such as poor maternal nutrition or placental insufficiency. These infants often eat voraciously and experience catch-up growth early in life. Children with constitutional growth delay usually grow normally over the first few years, but weight and height decelerate to near or below the 2nd percentile followed by growth at normal rates along their new curve (see Chapter 56 ). The symmetric deceleration of height and weight is a clue that the child does not have calorie insufficiency. Children with genetic causes of short stature have short height for age with appropriate low weight (see Table 12.1 ).

Children with FTT caused by calorie insufficiency typically have decreased weight gain, at first with sparing of height and head circumference (wasting). Long-standing calorie insufficiency results in height deceleration (stunting). Decrease in height or length is the best predictor of chronic malnutrition. Only in the worst, long-standing cases is head growth decreased. This typical pattern suggests calorie insufficiency and informs the clinician of the chronicity of the problem.

There are several approaches to the differential diagnosis. The functional approach determines whether there is a problem with inadequate calorie intake, increased calorie requirement or utilization, or increased calorie loss ( Table 12.2 ). The systems approach focuses on the identification of the organ system(s) responsible for poor growth ( Table 12.3 ).

Another approach is to consider the age at onset, the child’s developmental level, and the conditions likely to manifest at that stage of development. The causes of prenatal growth problems include environmental toxins, maternal drug and alcohol use, prenatal infection, congenital syndromes, placental insufficiency, and poor prenatal nutrition. Poor growth immediately after birth can be associated with maternal postpartum depression, bonding and attachment disorders, incorrect formula preparation, failure to establish breast-feeding, and congenital anomalies or metabolic conditions. Difficulty with transition to solid foods results in poor growth from 6 to 12 months. In children older than 9 months, issues of separation and autonomy may result in power struggles over eating, resulting in insufficient intake. For toddlers, poor food choices (empty calories found in juice drinks and snack foods), dysfunctional feeding interaction (restriction of self-feeding or lack of structure around meals), and distraction (chaotic home environment, television and electronic devices) may interfere with adequate food intake.