Nutrition and Growth Measurement

Measurement of growth and nutrition in the pediatric population

In clinical practice, an essential component of pediatric preventative care is the accurate measurement of growth in this population. Pediatric growth patterns are influenced by multiple factors, such as genetics, overall health, and proper nutrition. The pediatric provider must measure and follow these growth patterns over time to ensure the overall health and well-being of their pediatric patients.

Normal growth patterns are the criterion standard for clinicians to assess the general health of a child, and pediatricians must be well-versed in the normal and abnormal growth patterns for children. An infant or child’s deviation from a previously stable growth pattern is often the first sign of an underlying issue that requires close follow-up. Pediatricians need to be aware of risk factors for failure to thrive and obesity and the potential morbidity and mortality associated with these issues for the child. For these reasons, growth charts are a critical part of every pediatric health maintenance visit and play an important role in the nutritional assessment of the child.[1]

Obtaining accurate measurements of growth in pediatrics

The measurements of growth in pediatrics must be as accurate as possible. Those members of the office staff who are responsible for growth measurements should be trained in these skills in order to keep errors to a minimum. Ways to limit errors are as follows:

1. Taking multiple measurements (3 is ideal) with the mean measurement being plotted on a standardized growth chart (This helps to decrease observer variation.)

2. Using the same equipment each time

Note that measurement errors associated with child variation can exist. For example, a mean height variation of approximately 1.5 cm can exist between a measurement taken in a child upon wakening and then again in the late afternoon. Body weight variation from morning to evening is generally negligible.[2]

The importance of growth charts

Accurate measurements of growth, and plotting these measurements on the appropriate growth chart for a child's age and gender is an essential part of the pediatric physical examination. Growth is a fluid rather than a static measurement. Growth curves and charts allow pediatric providers to follow the growth of a child over time and assist them in picking up on deviations from a child's normal growth pattern that may point to an issue that requires closer monitoring or further investigation.

Two sets of growth charts are currently recommended for use by pediatric providers in the clinical outpatient setting. As of September 2010, the Centers for Disease Control (CDC) recommends using the growth charts developed by the World Health Organization (WHO) for children under the age of 2 and the charts developed by the CDC/ National Center for Health Statistics (NCHS) for children 2-20 years.

The WHO growth charts were released in 2006 and were based on the information obtained through the Multicenter Growth Reference Study (MGRS). This study described the growth of children raised under optimal conditions who were primarily breast fed. Data from 6 study sites (USA, Brazil, Norway, Ghana, India, and Oman), representing 5 continents were used to create these growth charts. These growth standards can be applied to all children regardless of ethnic background, socioeconomic status, and type of feeding.

The use of the WHO charts in the United States is less likely to lead to the categorization of a breastfed baby as being underweight. These growth charts define the normal range from -2SD to +2SD, which is approximately the 2nd and 98th percentiles, respectively. The WHO growth charts include the following:

1. Girls birth to 24 months length-for-age percentiles

2. Boys birth to 24 months length-for-age percentiles

3. Girls birth to 24 months weight-for-age percentiles

4. Boys birth to 24 months weight-for-age percentiles

5. Girls birth to 24 months weight-for-length percentiles

6. Boys birth to 24 months weight-for-length percentiles

7. Girls birth to 24 months head circumference-for-age percentiles

8. Boys birth to 24 months head circumference-for-age percentiles[3, 4]

The CDC/NCHS growth charts were updated in 2000 with an initial normal range of 5th to 95th percentiles; it was later modified to include 3 to 97th percentiles; however, the data points did not change. These charts were developed based on data from several national surveys conducted by the NCHS in the US from 1963-1994. The CDC/NCHS growth charts include the following:

1. Girls 2-20 years stature-for-age percentiles

2. Boys 2-20 years stature-for-age percentiles

3. Girls 2-20 years weight-for-age percentiles

4. Boys 2-20 years weight-for-age percentiles

5. Girls 2-20 years BMI-for-age percentiles

6. Boys 2-20 years BMI-for-age percentiles[4]

Normal and abnormal growth patterns

By monitoring a child's longitudinal growth pattern with the use of age-appropriate and gender -appropriate growth charts, pediatric providers can comment on normal growth patterns for individual children and note deviations from these patterns that may signal an underlying medical condition.

Normal patterns for the healthy neonate include a loss of up to 10% of their birth weight in the first week of life and generally regaining their birth weight by the end of their second week of life. After 2 weeks of age until 3 months, infants will gain approximately 20-30 grams per day. It is helpful to calculate this weight gain at office visits during this time.

As providers follow a child's growth over time, they notice if children track along the same percentile and often note this as the child "following their curve". There is a notable variation in this from ages 6-18 months. For healthy, term infants, their size at birth is a reflection of the intrauterine environment during gestation. By age 2, size is more strongly influenced by genetic factors, namely mean parental height. Therefore between ages 6 and 18 months, infants may change percentiles up or down to meet their genetic pre-disposition. This percentile generally corresponds to the percentile of the child's mean parental height with an appropriate weight to match. One can calculate mid-parental height in inches with the following formulas:

Boys: [(maternal height + 5) + paternal height] / 2

Girls : [maternal height + (paternal height - 5)] / 2

Abnormal growth patterns over time can point toward significant health issues. Some of these issues can be directly impacted by the nutritional status of the child.[1]

How measurements of growth can help assess nutritional status

Analysis of growth patterns in children can be helpful in detecting abnormal growth and may lead to an assessment of the child's nutritional status. The following chart is useful as a guide to growth and calorie requirements for children from birth to age 6 years.[1]

Table 1. Calorie Requirements for Children From Birth to Six Years (Open Table in a new window)

Adapted from National Research Council, Food and Nutrition Board: Recommended Daily Allowances, Washington, DC, 1989, National Academy of Sciences; Frank D, Silva M,Needlman R:Failure to thrive: myth and method, Contemp Pediatr 10:114, 1993[1]

Nutritional processes that can be diagnosed by abnormal growth patterns include failure to thrive and obesity.

Failure to thrive is often a diagnosis for children under age 3 years. It is suspected when a child's weight is below the 5th percentile, crosses 2 or more percentiles, or the weight-for-height is below the 5th percentile. Transient episodes of weight loss or poor weight gain secondary to brief illness generally correct themselves quickly and do not affect overall growth patterns. Alternatively, chronic malnutrition may cause stunted growth as well as poor weight gain, and the weight-for- height curves may not appear abnormal or concerning.[1, 5]

Another useful measurement when growth falls below the 5th percentile or above the 95th percentile is to calculate the percentage of ideal body weight. For example, a 9-month-old girl has a length of 70 cm (50th percentile for age). Her weight is 6.2 kg (less than 5th percentile for age). Her ideal weight (50th percentile for age) is 8.2 kg. Therefore her actual weight is 75% of the standard weight for her age.

The following numbers are useful table when calculating percent ideal body weight:

• >120% - Obese

• 110-120% - Overweight

• 90-110% - Normal variation

• 80-90% - Mild wasting

• 70-80% - Moderate wasting

• < 70% - Severe wasting

Numbers adapted from Nelson Textbook of Pediatrics 19th edition.[1]

In nutritional insufficiency, weight decreases before length is affected, resulting in a low weight-for-height. Poor linear growth is more likely to be due to congenital, constitutional, familial, or endocrine causes rather than due to nutritional deficits.

Congenital causes for short stature include chromosomal abnormalities, TORCH infection, extreme prematurity, or exposure to teratogens. For children with constitutional growth delay, weight and length decrease at the end of infancy, are low through childhood, and then accelerate at the end of adolescence to produce expected adult height. In familial short stature, children and parents are small and growth is parallel to normal curves. Children with endocrinopathies such as hypothyroidism, length/height tends to decline first, with an elevated weight-for-height ratio.

Obesity is another extreme of growth that has significant morbidity and mortality for children today. Obesity can be diagnosed with a BMI greater than the 95th percentile or a weight-for-height measurement of more than 120% of the mean for that age and gender. A BMI between the 85-95th percentiles falls in the overweight category.

Any child at the extremes of growth (failure to thrive and obesity) requires a thorough history and physical examination to evaluate for possible causes of the condition, as well as an in-depth evaluation to look for comorbidities associated with these conditions.[1, 5]

In pediatrics, the essential growth measurements in infants and toddlers to age 2 years are length, weight, head circumference, and weight-for-length. For children ages 3 years and up, the essential measurements are height, weight, and body mass index (BMI).

Measurement of growth in infants and toddlers

The measurement of length in children 2 years and younger is most accurate when 2 people can assist: one to position the child and one to measure. The child should be placed supine on a measuring board, and the measurement should be reported to the nearest 0.1 cm (see the image below). Measurement of weight in this population should be taken on a scale that has been properly calibrated. The infant/ toddler should be weighed without clothing or diaper, and the measurement reported to the nearest 0.1 kg. The ratio of weight-to-length is used to predict adiposity in children under the age of 2, rather than BMI. This measurement can also be plotted on a standardized growth chart.

Head circumference is measured in children up to age 3, as this is the time of greatest brain growth. It is correctly measured using a flexible tape measure at the maximum diameter through the supraorbital ridge to the occiput. The value should be reported to the nearest 0.01 cm and plotted on a standardized growth chart.[1]

Of note, head circumference should also be measured in older children with abnormal weight and height measurements, as it may provide insight into the underlying cause. Abnormal head growth is classified as either macrocephaly, greater than 2 standard deviations above the mean, or microcephaly, greater than 2 standard deviations below the mean.[5, 6]

Measurement of growth in older children

In children over the age of 2, height, weight and body mass index (BMI) are commonly measured (see image below). As noted in the previous section, head circumference may still be measured between the ages of 2-3 years. In children older than 2 years, standing height rather than recumbent length is measured. The measurement should be performed without shoes using a stadiometer. The mean of 3 measurements should be taken to ensure the greatest accuracy, and it should be plotted on a standardized growth curve.

Of note, length is about 1 cm greater than standing height. Height velocity can also be measured by looking at the centimeters grown in a year (cm/yr) and can be plotted on a standardized curve;[7] it is valuable in detecting growth abnormalities early in the course of chronic illness. Weight should be measured without shoes and little/no outer clothing. It should be reported to the nearest 0.1 kg and plotted on a standardized growth curve.

Body mass index is derived from the measurements of height and weight and shows the relative proportion between the 2; it is a valid predictor of adiposity.[8] BMI will vary based on gender, age, and pubertal stage. The calculation for BMI is as follows:

• Weight (kg) / height (m) 2

BMI has been recommended as the most appropriate single indicator of an overweight patient and obesity in the pediatric population in the clinical setting. The measurements required to calculate BMI are done routinely at pediatric health maintenance visits and are noninvasive, inexpensive, and easily understood.[2] BMI values are then to be plotted on a BMI reference chart; a child with a BMI greater than the 85th percentile is overweight, and a child with a BMI greater than the 95th percentile is obese. Children with a BMI less than the 5th percentile are considered underweight.

Other methods can be used to measure adiposity more directly. These include measurements of the triceps and subscapular skinfolds (see the images below). However, skinfold measurements can be difficult to obtain in the outpatient clinical setting. A recent study showed that, for children 5-18 years of age, BMI-for-age, triceps skinfold-for-age, and subscapular skinfold-for-age individually all performed equally well in the classification of excess body fat.[9]

Other measurements of growth in pediatrics

Body proportions

At birth, the head and trunk are large relative to the rest of the body. The limbs continue to lengthen during the course of development, especially during puberty. This can be quantified by obtaining upper body segment and lower body segment measurements. The lower body segment is the measurement of the length from the pubic symphysis to the floor; the upper body segment is the height minus the lower body segment. The U/L ratio (upper body segment : lower body segment) at birth is about 1.7; at age 3 years it is 1.3; at greater than 7 years, it is 1.0 with the upper body segment and lower body segment being about equal. Of note, higher U/L ratios are noted in short-limb dwarfism and other bone disorders such as rickets.

Skeletal maturation

Bone age and stages of pubertal development are closely correlated and can be helpful in predicting adult height in early or late-developing adolescents. Skeletal maturity is more closely linked to sexual maturity than it is to chronological age.

Dental development

The sequence of events in dental development includes mineralization, eruption, and exfoliation. Mineralization can begin as early as the 14th week of gestation and continues until approximately age 3 years for the primary teeth. Tooth eruption begins with the central incisors and continues laterally. Delayed tooth eruption is classified by the absence of any teeth by 13 months of age; possible causes of this include hypothyroidism, hypoparathyroidism, or idiopathic delayed eruption (most common). Exfoliation begins around 6 years of age and continues until around age 12 years. Some causes of early exfoliation to consider are histiocytosis X, cyclic neutropenia, leukemia, trauma or idiopathic causes.[1]