Assessment of Growth

Techniques to Measure Growth

Growth assessment requires accurate and precise measurements. For infants and toddlers age <2 yr, weight, length, and head circumference are obtained. Head circumference is measured with a flexible tape measure starting at the supraorbital ridge around to the occipital prominence in the back of the head, locating the maximal circumference. Height and weight measures should be performed with the infant naked, and ideally, repeated measures will be performed on the same equipment. Recumbent length is most accurately measured by two examiners (one to position the child). Hair ornaments and hairstyles that interfere with measurements and positioning should be removed. The child's head is positioned against an inflexible measuring board in the Frankfurt plane , in which the outer canthi of the eyes are in line with the external auditory meatus and are perpendicular to the long axis of the trunk. Legs should be fully extended, and feet are maintained perpendicular to the plane of the supine infant. For older children (>2 yr) who can stand unassisted, standing heights should be obtained without shoes, using a stadiometer with the head in the Frankfurt plane, and the back of the head, thoracic spine, buttocks, and heels approximating the vertical axis of one another and the stadiometer.

Measurements obtained using alternative means, such as marking examination paper at the foot and head of a supine infant or using a tape measure or wall growth chart with a book or ruler on the head can lead to inaccuracy and render the measurement useless.

Measurements for height and weight should be plotted on the age-appropriate growth curve. Comparing measurements with previous growth trends, repeating measures that are inconsistent, and plotting results longitudinally are essential for monitoring growth. Calculation of interim linear height velocity, such as centimeters per year (cm/yr), allows more precise comparison of growth rate to the norm ( Table 27.1 ).

If a child is growing faster or more slowly than expected, measurement of body proportions, which follow a predictable sequence of changes with development, are useful. The head and trunk are relatively large at birth, with progressive lengthening of the limbs throughout development, particularly during puberty. The upper-to-lower body segment ratio ( U/L ratio ) provides an assessment of truncal growth relative to limb growth. The lower-body segment is defined as the length from the top of the symphysis pubis to the floor, and the upper-body segment is the total height minus the lower-body segment. The U/L ratio equals approximately 1.7 at birth, 1.3 at 3 yr, and 1.0 after 7 yr. Higher U/L ratios are characteristic of short-limb dwarfism, as occurs with Turner syndrome or bone disorders, whereas lower ratios suggest hypogonadism or Marfan syndrome.

Arm span also provides assessment of proportionality and is measured as the distance between the tips of the middle fingers while the patient stands with the back against the wall with arms outstretched horizontally at a 90-degree angle to the trunk. This span should be close to height, although the proportion changes with age.

Growth Curves

The American Academy of Pediatrics (AAP) and the U.S. Centers for Disease Control and Prevention (CDC) recommend use of the 2006 World Health Organization (WHO) growth curves for children age 0-24 mo and the 2000 CDC growth curves for children age 2-19 yr ( https://www.cdc.gov/growthcharts ). There are 5 standard gender-specific charts: (1) weight for age, (2) height (length and stature) for age, (3) head circumference for age, (4) weight for height (length and stature) for infants, and (5) body mass index for age ( Fig. 27.1 ; see also Fig. 23.1, Fig. 23.2, Fig. 25.1 ). Clinicians should confirm that the correct CDC and WHO growth charts are used in electronic medical records to ensure accurate characterization of growth.

The WHO curves describe growth differently than the CDC curves ( Fig. 27.2 ). The WHO curves are growth standards that describe how children grow under optimal conditions, whereas the CDC curves are growth references that describe how children grew in a specific time and place. The WHO growth curves are based on longitudinal growth studies in which cohorts of newborns were chosen from six countries (Brazil, Ghana, India, Norway, Oman, United States) using specific inclusion and exclusion criteria; all infants were breastfed for at least 12 months and were predominantly breastfed for the first 4 mo of life. They were measured regularly from birth to 23 mo during 1997–2003. In contrast, the CDC curves are based on cross-sectional data from different studies during different time points. Growth curves for children age 2-59 mo were based on the National Health and Nutrition Examination Survey (NHANES), which included a cross section of the U.S. population. These data were supplemented with additional participants in a separate nutrition surveillance study.

Several deficiencies of the older charts have been corrected, such as the overrepresentation of bottle-fed infants and the reliance on a local dataset for the infant charts. The disjunction between length and height when transitioning from the infant curves to those for older children is improved.

Each chart is composed of percentile curves, which indicate the percentage of children at a given age on the x axis whose measured value falls below the corresponding value on the y axis. The 2006 WHO growth curves include values that are 2 standard deviations (SD) above and below median (2nd and 98th percentiles), whereas the 2000 CDC growth curves include 3rd and 97th percentiles. On the WHO weight chart for boys age 0-24 mo (see Fig. 23.2 A ), the 9 mo age line intersects the 25th percentile curve at 8.3 kg, indicating that 25% of 9 mo old boys in the WHO cohorts weigh less than 8.3 kg (75% weigh more). Similarly, a 9 mo old boy weighing more than 11 kg is heavier than 98% of his peers. The median or 50th percentile is also termed the standard value , in the sense that the standard length for a 7 mo old girl is 67.3 cm (see Fig. 23.2 B ). The weight-for-length charts (see Fig. 23.1 ) are constructed in an analogous fashion, with length or stature in place of age on the x axis; the median or standard weight for a girl measuring 100 cm is 15 kg.

Extremes of height or weight can also be expressed in terms of the age for which they would represent the standard or median. For instance, an 18 mo old girl who is 74.9 cm (2nd percentile) is at the 50th percentile for a 13 mo old. Thus the height age is 13 mo. Weight age can also be expressed this way.

In assessing adolescents, caution must be used in applying cross-sectional charts. Growth during adolescence is linked temporally to the onset of puberty, which varies widely. Normal variations in the timing of the growth spurt can lead to misdiagnosis of growth abnormalities. By using cross-sectional data based on chronological age, the charts combine youth who are at different stages of maturation. Data for 12 yr old boys include both earlier-maturing boys who are at the peak of their growth spurts and later-maturing ones who are still growing at their prepubertal rate. The net results are an artificially blunted growth peak, and the appearance that adolescents grow more gradually and for a longer duration than in actuality.

When additional insight is necessary, growth charts derived from longitudinal data, such as the height velocity charts of Tanner and colleagues, are recommended. The longitudinal component of these velocity curves are based on British children from the 1950s–1960s, and cross-sectional data from U.S. children were superimposed. More recently, height velocity curves based on longitudinal data from a multiethnic study conducted at five U.S. sites included standard deviation scores for height velocity for earlier- and later-maturing adolescents to facilitate the identification of poor or accelerated linear growth.

Specialized growth charts have been developed for U.S. children with various conditions, including very low birthweight, small for gestational age, trisomy 21, Turner syndrome, and achondroplasia, and should be used when appropriate.

Facilitating identification of obesity, the charts include curves for plotting body mass index (BMI) for ages 2-20 yr rather than weight for height (see Fig. 27.1 ). Methodological steps have ensured that the increase in the prevalence of obesity has not unduly raised the upper limits of normal. BMI can be calculated as weight in kilograms/(height in meters) ² or weight in pounds/(height in inches) ² × 703, with fractions of pounds and inches expressed as decimals. Because of variable weight and height gains during childhood, BMI must be interpreted relative to age and sex; BMI percentile provides a more standardized comparison. For example, a 6 yr old girl with BMI of 19.7 kg/m ² (97th percentile) is obese, whereas a 15 yr old girl with BMI of 19.7 kg/m ² (50th percentile) is normal weight.