Department of Pediatrics, University of Hawaii John A. Burns School of Medicine

February 2003

A 4 month old Asian female comes to your office for her scheduled well baby checkup. She was born at 39-4/7 weeks gestation by normal spontaneous vaginal delivery without any complications. At birth, her weight was 3856 g, length 53 cm, head circumference 34 cm, and chest circumference 35.5 cm. She was discharged from the nursery at 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), head circumference 43 cm (90%tile), and chest circumference 41 cm. 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. There are two age group specific growth charts, one for children from birth to 36 months of age, and another from 2 years to 20 years of age.

The National Center For Health Statistics (HCHS) of the Centers for Disease Control and Prevention, recently released new standard growth charts in 2000 that remedy many of the deficiencies present in older growth charts. The new growth charts are based on a national representative sample collected from 1988 to 1994 as part of the National Health and Nutrition Examination Survey (NHANES-III), and they better represent the combined growth patterns of breast-fed and formula-fed infants. The larger, pooled data sets used to create the revised charts eliminate the problem of differing percentiles when making the transition from recumbent length to stature height. Lastly, the weight for height curves have been replaced by body mass index (BMI) curves. Other new features of the new growth charts are the extension to 20 years because of sufficient data being available and its desirability for general populations, particularly for clinics dealing with endocrine disorders and congenital abnormalities (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 (2). 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 (3). Unfortunately, these charts are based on a relatively small, possibly non-representative sample (4). If the NCHS 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 (5). 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 (4). A 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) (6). 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 beyond the scope of this chapter. 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 (7), 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 (8).

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 5th percentile or drops more than two major percentile lines. 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 (9).

When curves are outside the 5th and 95th percentiles, 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.

The weight for height curves exceeding 120% of the median weight for height can also be an indicator for obesity. The problem with the weight for height curves is that they are applicable only from 2 years to 11.5 years for males and up to 10 years for females because of weight for height changes occurring with age after pubescence. The new growth charts remedy this by including the body mass index (BMI), which is weight in kilograms divided by the square of the height in meters. 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 therefore must be based on percentiles, 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 predict those individuals who are at risk for obesity later in childhood and adulthood. 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 (1).

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 (4).

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. How 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. Roche AF, Guo SS. The New Growth Charts. Pediatric Basics 2001;94:2-13. The new 2000 growth charts by the CDC can be downloaded from the web site, http://www.cdc.gov/growthcharts/. For PDA users, there is a CDC 2000 growth chart program developed by Dr. Andre S. Chen, which can be obtained at http://www.statcoder.com. This program includes a calculation for BMI. Two medical calculators that can also be used to calculate BMI are MedCalc by Dr. Mathias Tschopp, which can be obtained at http://netxperience.org/medcalc, and MedMath by Dr. Phillip Cheng, which can be downloaded at http://www.pdacentral.at/palm/preview/45487.html.

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

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

4. 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.

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

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

7. 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.

8. 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.

9. 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.

Answers to questions

1. BMI (kg/m2) = weight in kilograms divided by the square of the height in meters.

2. First 18 months of life.

3. a) If the child's weight is below the 5th percentile, or b) if weight drops more than two major percentile lines.

4. 85th percentile.

5. 30 grams, or 1 oz 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).