Standard measurement techniques should be used for all growth parameters.298 Ideally, length/height and head circumference measures should be performed by the same person each time.
Measured in children up to approximately 24 months of age or in older children who are unable to stand without assistance.
Equipment
Infant stature board with a fixed headboard and a moveable footboard positioned perpendicular to the table surface and a rule along 1 side; pen and paper for recording. Two persons are necessary: 1 to hold the head and another to measure.
Procedure
(i) The infant may be measured in light clothing, without foot coverings. (ii) Place the infant on the table, lying on his back. (iii) Hold the crown of the infant's head and bring it gently in contact with the fixed headboard. Align the external auditory meatus and the lower margin of the eye orbit perpendicular to the table. (iv) While the head remains in contact with the headboard, a second measurer grasps 1 or both feet at the ankle. (v) Move the footboard close to the infant's feet as the legs are gently straightened. Bring the footboard to rest firmly against the infant's heels, making sure the toes point straight upward and the knees are pressed down on the table. (vi) Read the markings on the side of the measuring board and record the value to the nearest 0.1 cm.
HEIGHT
Measures the child who is able to stand unassisted.
Equipment
Fixed measuring device attached to a wall (stadiometer); block squared at right angles or moveable head projection attached at right angle to the board; pen and paper for recording.
Procedure
(i) Have the child remove his or her shoes and stand on the floor, facing away from the wall with heels together, back as straight as possible, arms straight down; heels, buttocks, shoulders, and head touching the wall or vertical surface of the measuring device. A family member or other measurer may be necessary to hold the child's ankles and knees steadily in place. The child's axis of vision should be horizontal, with the child looking ahead and the external auditory meatus and lower margin of the orbit aligned horizontally. (ii) Place the head projection at the crown of the head. (iii) Hold the block steady and have the child step away from the wall. (iv) Note the measurement and record it to the nearest 0.1 cm. (v) Perform 3 measurements that are within 0.2 cm of each other and use the average of the 3 for the final value.
Equipment
Infant scale that allows infant to lie down; pen and paper for recording.
Procedure
(i) Undress the infant completely. (ii) Place a clean paper liner in the tray of the scale. (iii) Calibrate the scale to zero. (iv) Lay or seat the infant in the tray. (v) Read the weight according to the type of scale. Make sure the infant is unable to touch the wall or surrounding furniture. (vi) Record the weight to the nearest 0.1 kg.
Equipment
Scale; pen and paper for recording.
Procedure
(i) The child should be weighed in light clothing without footwear. (ii) Calibrate the scale to zero. (iii) Assist the child onto the platform of the scale. (iv) Instruct the child to stand in the center of the platform with feet flat and heels touching, as erect as possible. (v) If using a beam scale, adjust the beam of the scale with the main and fractional poise as necessary until the beam swings freely and comes to rest parallel to the scale platform. Activate the digital scale, if this is the scale used. (vi) Read the measurement from the scale, looking squarely at the increments rather than from an angle. (vii) Record the weight to the nearest 0.1 kg.
Measured in children up to 36 months of age.
Equipment
Firm nonstretchable measuring tape; pen and paper for recording.
Procedure
(i) Have the person assisting hold the infant so that the head is upright. (ii) Locate the occipital bone at the back of the head, also the supraorbital ridges. (iii) Apply the tape firmly around the head just above the supraorbital ridges at the same level on both sides to the occiput. Move the tape up or down slightly to obtain the maximum circumference. The tape should have sufficient tension to press the hair against the skull. (iv) Record the measurement to the nearest 0.1 cm.
Anthropomorphic measures should be plotted on the appropriate growth chart: standing height or recumbent length, weight, BMI, and head circumference. Low height for chronological age or a low head circumference in proportion to height may reflect long-term nutritional deficits, particularly in infants. Parental heights should be considered when interpreting growth charts. One-time measurements reflect size, whereas serial measurements are necessary for the assessment of growth. Low BMI-for height-age may reflect a nutritional deficit. In some situations, BMI may be better assessed relative to chronological age; for example, in a fully mature (Tanner stage 5) adolescent.
Individual measurements are evaluated by determining SDS (or z scores) or percentiles. Growth SDS represent the difference, in SD units, of an individual child's value (eg, height or weight) and the mean value of a sample population (eg, mean height or weight of healthy children of the same age and sex). Percentiles and SDS are interchangeable; they are 2 ways of expressing the same information. For example, a child on the 50th percentile of height for age would have an SDS of 0. About 95% of healthy children will have an SDS between -2.0 (~3rd percentile) and +2.0 (~97th percentile).
Measures may be plotted on the standardized growth charts enclosed in these guidelines (Appendix 5).33,34,52 These growth charts were generated by using a statistical method called LMS.520 Calculation of exact SDS can be done by using data from tables of L, M, and S values for each measure and entering them into the following equation:
SDS = [(observed measure ÷ M)L - 1] ÷ (L × S)
The US National Center for Health Statistics 2000 Growth Charts LMS tables are available on-line at: www.cdc.gov/nchs/about/major/nhanes/growthcharts/datafiles.htm.
The WHO Growth Standards LMS tables are available in downloadable documents34,52 online at: www.who.int/childgrowth/standards/technical_report/en/index.html.
EXAMPLE: To calculate the height-for-age SDS for an 8.5-year-old girl, one would look up the L, M, and S values from the appropriate table and enter them into the equation, along with her observed height (eg, 120.6 cm):
SDS = [(120.6 ÷ M)L - 1] ÷ (L × S)
SDS = [(120.6 ÷ 130.6)0.0027 - 1] ÷ (0.0027 × 0.0463)
SDS = -1.72
Alternatively, several on-line calculators or downloadable software packages are available to perform these calculations. On-line resources, the data sources for each, and the measures included in each are provided in Appendix 2.