Vince K. Yamashiroya, MD

May 2013

* A 4 month old female comes to your office for her scheduled well baby checkup. She was born at 39 weeks gestation by normal spontaneous vaginal delivery without any complications. At birth, her weight was 3856 g, length 53 cm, and head circumference 34 cm. She was discharged from the nursery by 48 hours of life. She has been breast-fed since birth, although her mother started to also use formula between one to two months of age. She is now being breast-fed once a day, given pumped breast milk in a bottle two to three times a day, and formula the rest of the time (about 16 oz or 480 ml per day). She has 2 to 3 bowel movements a day with many wet diapers. Her past medical history is otherwise significant for a vibratory heart murmur heard from the second week of life, which was thought to be innocent. Parents have no concerns. *

* Exam: VS are normal. Weight 7.4 kg (95%tile), length 64 cm (90%tile), and head circumference 43 cm (90%tile). She is a robust, active and healthy appearing infant. Her heart murmur has resolved and the rest of her examination is otherwise normal. *

The monitoring of a child's growth is probably the most important job for a pediatrician. It is not only essential for the general pediatrician, but for other subspecialties as well. An aberration in growth patterns is often the first clue that there is something wrong with the child. Often, the growth of the child is used in conjunction with other signs and symptoms to help the physician determine what the problem might be. An older child who is not gaining weight could be the first clue to inflammatory bowel disease. A girl who is short in stature may have Turner syndrome. A baby with an abnormally increasing head size might have hydrocephalus.

The most important tool for assessing and monitoring a child's growth is the growth chart which plots height (length), weight, and head circumference. There are different growth charts for boys and girls and two age-group specific growth charts. What can be confusing is that there are two organizations that have made growth charts for healthy children, the Centers for Disease Control (CDC) and the World Health Organization (WHO). There are big differences in both and in 2010, the CDC recommends that WHO growth charts be used for children from 0 to 2 years of age, and the CDC growth charts be used in children from 2 years of age and older (1). The reason why WHO growth charts are used for children less than 2 years of age are WHO establishes growth of the breastfed infant as the norm for growth, provides a better description of physiological growth in infancy in optimal conditions, and is based on a high quality study with data obtained at frequent intervals. For children over the age of 2 years, the CDC growth chart is used since it can be used in children from 2 to 20 years of age (whereas the WHO growth chart only goes up to 5 years of age), and the methods used to create the growth charts are similar in both the CDC and WHO (2).

The WHO growth chart is based on the Multicentre Growth Reference Study which looked at how healthy children should be growing under optimal conditions and therefore can be called a growth "standard". The data is based on children from different ethnic populations and cultural settings. The CDC growth chart is based on the National Center for Health Statistics (HCHS) and was updated in 2000 to include more breastfed babies and different ethnic populations. Compared to the WHO growth charts which looked at children living in different countries under optimal healthy conditions, the CDC growth charts are based on the growth of children living in the United States from 1963 to 1994. Therefore, there will be differences in percentiles when a child transitions from the WHO growth chart to the CDC growth chart at 2 years of age (3). Both of these growth charts can be found at the CDC website at http://www.cdc.gov/growthcharts/ (1).

It should be noted that these growth charts are reflective of the population who are healthy and born at term. There are other growth charts available for children with various conditions, such as Turner, Klinefelter, and Down syndromes, and achondroplasia (4). Special growth charts for premature babies are also available by Babson and Benda that are based on gestational rather than chronological age, beginning at 26 weeks of gestation (5). Unfortunately, these charts are based on a relatively small, possibly non-representative sample (6). If the WHO or CDC growth charts are used, however, the child's growth parameters (weight, height, head circumference) should be adjusted for prematurity until 24 months of age or up to three years for infants born at less than 1500 grams (7). Very low birth weight (VLBW, <1,500 g) infants may continue to show catch-up growth through early school age.

It is essential to look at the trajectory of the child's growth curve. Typically, infants and children stay within one or two growth percentile channels, which is due to the control that genes exert over body size. A growth channel is the area between the percentile lines. A normal exception occurs during the first two years of life. For full term infants, size at birth reflects the influence of the uterine environment. Size at age 2 years correlates with mean parental height, reflecting the influence of genes. Therefore, from birth through 18 months, small infants will often shift percentiles upward toward their parents' mean percentile, and large infants will shift downwards (6). Tanner's height prediction formula can be used to calculate the estimated adult height by taking the mid-parental height (mother's height + father's height, divided by 2), and adding 6.5 cm for males, and subtracting 6.5 cm for females, with a range of 2 standard deviations (one standard deviation is about 5 cm) (8). Another way of estimating adult height is to double the height at 24 months of age for boys, and double the height at 18 months of age for girls. Growth is influenced by many factors, including nutrition, chronic disease, etc., therefore, this formula is based purely on genetic potential.

In adolescents, normal variations in the timing of the growth spurt can lead to a misdiagnosis of growth abnormalities. In primary care, it is important to know the relationship between sexual maturity and growth, which is discussed in other chapters. However, a few general rules can be kept in mind. Before the onset of puberty, the average height velocity is about 5 to 6 cm per year. In females, peak height velocity occurs about 2 years after the growth spurt begins and averages about 9 cm per year. This is also around the time when the nipple and areola have developed but before any other significant breast development (9), and about 6 to 12 months prior to menarche. After menarche, females will usually not grow more than 5 cm, with epiphyseal closure occurring about 2 years after. In males, peak height velocity occurs later and averages about 10 cm per year. This is about the time that the male's genitalia are fully developed. Males are taller because of this greater velocity of height in addition to having about 2 more years of prepubescent growth over females (10).

The growth curve is not linear but rather sigmoidal. Growth normally starts to slow down at about 12 to 15 months of age, which is reflected in the growth chart. The periods of rapid growth occur during the first 12 months of age, and from puberty until adulthood. The growth chart is an essential tool to diagnose failure to thrive (FTT) or growth failure. Although there are no universal criteria for FTT, most consider the diagnosis if the child's weight is below the 2nd percentile and/or drops two or more major percentile lines, considering that the child does not have any genetic abnormalities. Children who are below the 2nd percentile and who has a normal weight gain velocity do not have FTT (11). Calculation of weight gain in grams per day also allows more precise estimation of growth rate as can be seen in the table below. Neonates should gain weight at a rate of 15 g/kg/day (12). Another way of estimating what weight should be is that birth weight doubles at 6 months and triples at 1 year of age.

Note: 30 g = 1 oz.

When curves are outside the percentile ranges of the chart, it is useful to mention the age at which the growth parameter is at its median value (50th percentile). For example, if a 10 year old female weighs 18 kg, this weight is below the 5th percentile for a 10 year old; and, it is at the 50th percentile for a 5 year old. One could state that her weight age is 5 years, which is a better quantitative description of the growth abnormality.

Lastly, the CDC growth curves identify obesity by measuring the body mass index (BMI), which is calculated by the weight in kilograms divided by the square of the height in meters (or weight in pounds divided by the square of the height in inches multiplied by 703). In adults, a BMI value greater than 25 units is widely accepted as being overweight and a value larger than 30 units is accepted as obesity. However, since the cutoff values for children differ with age and sex, they must be based on percentiles (also known as Z scores), with the 85th percentile being suggested as the cutoff point for being overweight. This percentile is also justified by studies showing that the risk of large BMI values in adulthood and the prevalence of cardiovascular and other diseases increase dramatically for children ages 8 years and older who are over the 85th percentile for BMI. BMI values decrease from 2 years to 5 years of age, after which there is an increase to 20 years of age. The changes with age in BMI reference values reflect normal alterations in total body fat and fat-free mass. Fat-free mass increases with age in both sexes, but increases are more rapid in boys than in girls after age 13. Likewise, total body fat increases from 8 to 18 years in girls but decreases after age 14 in boys. Another interesting point is the time of rebound, or the point when the BMI values change from decreasing to increasing. It has been observed that individuals who rebound earlier than 5 years of age have higher BMI compared to those who rebound later after 5 years of age. This helps in predicting those individuals who are at risk for obesity later in life. The disadvantage of using BMI is that it does not provide an accurate index of adiposity since it does not differentiate between lean tissue and bone from fat. However, BMI values correlate with total body fat, fat as a percentage of body weight (percent body fat), and the mass of all lean tissues (fat-free mass). Although percent body fat is the best measure of obesity, its measurement requires complex laboratory procedures. When BMI is used to identify obese children, there are many false negatives (obese children not identified) but few false positives (non-obese children classified as obese). Therefore, for the easy recognition of obese children, BMI is preferred over triceps skinfold thickness in girls, but triceps skinfold thickness may be more useful in boys (13).

Common student and board examination questions include the growth chart patterns for various diseases and conditions such as constitutional growth delay, familial short stature, nutritional insufficiency, and congenital pathologic short stature. The following list describes the characteristics of each (6).

1. Congenital pathologic short stature: These infants are born small and growth gradually tapers off throughout infancy. These babies are born with intrauterine growth retardation (IUGR), and are small for gestational age (SGA). Examples are chromosomal abnormalities, TORCH infections, teratogens, extreme prematurity, maternal smoking, etc.

2. Constitutional growth delay: In this type of delay, these patients enter puberty later; therefore, their growth spurt occurs later in adolescence. The growth curve has the following appearance: weight and height drop in their percentiles near the end of infancy, parallel the norm through middle childhood, and accelerate toward the end of adolescence. Adult size is normal or often taller than average because their duration of growth is longer than others. Frequently, one or both parents may have a history of short stature during childhood, delayed puberty, and eventual normal adult height. Delayed puberty can be identified by asking about age of menarche in mother and age at which father first started shaving. Tanner staging is also useful in evaluating these patients because of their delayed puberty.

3. Familial short stature: Infant and parents are small. Growth runs parallel to and just below the normal curves.

4. Nutritional insufficiency: In this condition, weight declines before length. Body mass index is also low.

Questions

1. What is the formula for calculating BMI?

2. At what age does the uterine environment play a role in the growth of a child versus the influence on growth by the genetic makeup?

3. What are two ways failure to thrive are recognized in a growth chart?

4. What percentile of BMI is considered the cutoff point for being overweight?

5. What is the approximate weight gain in grams per day for a healthy term infant from birth to 3 months of age?

6. At what age does rebound occur in BMI? If a child rebounds early, what is this predictive of?

7. What is a weakness of using BMI to identify obesity?

8. What do the growth curves for congenital pathologic short stature, constitutional growth delay, and familial short stature look like?

9. What is the formula used to estimate a child's adult height (Tanner's height prediction formula)?

References

1. Growth Charts. (n.d.) From Centers for Disease Control and Prevention. Retrieved from http://www.cdc.gov/growthcharts/.

2. Growth Charts. (n.d.). From Centers for Disease Control and Prevention. Retrieved from http://www.cdc.gov/growthcharts/who_charts.htm.

3. Bloom JA. Normal growth patterns in infants and prepubertal children: Treatment. In: Up-to-Date. June 19, 2012, Amsterdam: Wolters Kluwer.

4. Siberry GK. Growth Charts. In: Siberry GK, Iannone R. The Harriet Lane Handbook, 15th edition. 2000, Missouri: Mosby, Inc., pp. 283-306.

5. Babson SG, Benda GI. Growth graphs for the clinical assessment of infants of varying gestational age. J Pediatr 1976;89:815.

6. Needlman RD. Chapter 15-Assessment of Growth. Behrman RE, et al (eds). Nelson Textbook of Pediatrics, 16th edition. 2000, Philadelphia: W.B. Saunders Company, pp. 57-61.

7. Dixon SD, Stein MT. Encounters with Children: Pediatric Behavior and Development, third edition. 2000, St. Louis: Mosby, p. 159.

8. Keefer JR. Endocrinology. In: Siberry GK, Iannone R. The Harriet Lane Handbook, 15th edition. 2000, Missouri: Mosby, Inc., pp. 207-228.

9. Garibarldi L. Chapter 571-Physiology of Puberty. In: Behrman RE, et al (eds). Nelson Textbook of Pediatrics, 16th edition. 2000, Philadelphia: W.B. Saunders Company, pp. 1687-1688.

10. Neinstein LS, Kaufman FR. Normal physical growth and development. In: Neinstein LS (ed). Adolescent Health Care: A Practical Guide, 3rd ed. 1996, Baltimore, MD: Williams & Wilkins, pp. 3-39.

11. Kirkland RT, Motil KJ. Etiology and evaluation of failure to thrive (undernutrition) in children younger than two years. In: Up-to-Date. July 31, 2012, Amsterdam: Wolters Kluwer.

12. Needlman RD. Chapter 10-The First Year. In: Behrman RE, et al (eds). Nelson Textbook of Pediatrics, 16th edition. 2000, Philadelphia: W.B. Saunders Company, pp. 32-38.

13. Roche AF, Guo SS. The New Growth Charts. Pediatric Basics 2011;94:2-13.

Answers to questions

1. BMI = weight in kilograms divided by the square of the height in meters. (Or pounds/inches squared x 703.)

2. First 18 months of life.

3. a) If the child's weight is below the 2nd percentile, and b) if weight drops more than two major percentile lines.

4. 85th percentile.

5. 30 grams (1 ounce) per day.

6. At 5 years of age. Those who rebound before 5 years have a higher risk of obesity in childhood and adulthood.

7. It does not provide an accurate index of adiposity since it does not differentiate between lean tissue and bone from fat.

8. Congenital pathologic short stature: infant born small and growth gradually tapers off throughout infancy. Constitutional growth delay: weight and height drop in their percentiles near the end of infancy, parallel the norm through middle childhood, and accelerate toward the end of adolescence. Adult size is normal. Familial short stature: Infant and parents are small. Growth runs parallel to and just below the normal curves.

9. Predicted adult height = (mother's height + father's height) divided by 2, and adding 6.5 cm for males, and subtracting 6.5 cm for females, with a range of 2 standard deviations (one standard deviation is about 5 cm).