Excerpt from Failure to Thrive

Synonyms, Key Words, and Related Terms: failure to thrive, FTT, growth failure, failure of growth, malnutrition, delayed growth, growth charts, infant growth, normal growth, growth in infants, normal weight in infants, normal height in infants, head circumference in infants

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Background: Growth failure, or failure to thrive (FTT), is a descriptive term and not a specific diagnosis. Although definitions vary, most authors use this term only when growth has been noted to be low or to have decreased over time. For instance, some authors define FTT as height or weight less than the third to fifth percentiles for age on more than one occasion. Other authors cite height or weight measurements falling 2 major percentile lines using the standard growth charts of the National Center for Health Statistics (NCHS). Still others state that true malnutrition (weight <80% of ideal body weight for age) should be present to state a child is failing to thrive. All authorities agree that only by comparing height and weight on a growth chart over time can FTT be assessed accurately. Although measurements of head circumference are important in the evaluation of infants and toddlers, failure of the head to grow by itself is not part of the FTT entity.

Normal growth and growth charts of term and premature infants, as well as the etiology, evaluation, management, and outcome of FTT are discussed in this article.

Pathophysiology:

Normal growth in term infants

To recognize abnormal growth, one needs to understand normal growth. The average birth weight for a term infant is 3.3 kg. Weight drops as much as 10% in the first few days of life, probably as a result of loss of excess fluid; however, birth weight should be regained within 2 weeks after birth. Breastfed infants tend to regain birth weight a little later than bottle-fed infants.

The median increase in weight per day in children is summarized in Table 1. On average, infants gain 1 kg/mo for the first 3 months, 0.5 kg/mo from age 3-6 months, 0.33 kg/mo from age 6-9 months, and 0.25 kg/mo from age 9-12 months. Term infants double their birth weight by age 4 months and triple their weight by age 12 months.

Table 1. Median Daily Weight

Age Median Daily Weight Gain, grams

0-3 mo 26-31 g

3-6 mo 17-18 g

6-9 mo 12-13 g

9-12 mo 9 g

1-3 y 7-9 g

4-6 y 6 g

Term infants grow 25 cm in length during the first year, 12.5 cm in the second year, and then slow down to approximately 5-6 cm between age 4 years and the onset of puberty, at which time growth can increase up to 12 cm per year.

The average head circumference is 35 cm at birth and increases rapidly to 47 cm by age 1 year; the rate of growth then slows, reaching an average of 55 cm by age 6 years.

Also, the upper-to-lower body segment ratio changes with growth. Normally, the ratio at birth is 1.7, the ratio at age 3 years is 1.3, and the ratio by age 7 years becomes 1.0. The lower body segment is the measurement of the symphysis pubis to the floor.

Normal growth in premature infants

When plotting growth charts for premature babies, a "corrected age" should be used. This corrected age can be calculated by subtracting the number of weeks of prematurity from the postnatal age. Special growth charts based on gestational age rather than chronological age have been developed for infants, beginning at 26 weeks’ gestational age; however, because these charts represent a compilation of a relatively small number of infants, they may not be completely reliable. Whichever technique is used for premature babies (eg, adjustment of age, using specific premature growth charts), consistency of methodology is essential. Once a method for plotting growth is chosen, that technique should be followed each time plotting occurs.

After catch-up growth is attained, .....