Age Years

figure 2-4 Correlations between adult height and height of the same individuals as children. (Source: Tanner J. Growth at Adolescence, 2nd ed. Oxford: Blackwell Scientific Publications, 1962.)

was carried out in the 1930s by Sir John Hammond at Cambridge University.6 Using artificial insemination techniques, this research group crossed a Shetland pony mare with a Shire horse sire, and a Shire horse mare with a Shetland pony sire. Birth-weights of the foals were in accordance with maternal size. The offspring of the large mother had a greater birth weight than that of the small mother, even though both offspring shared the same proportion of genes from each parent. This action is not gene mediated, and many studies of the relationship between size of the child at different ages and size of parents confirm this statement. This is an adaptive mechanism from the evolutionary point of view: It allows a genetically large fetus to be delivered by a small mother, with less risk of having a dangerous labor due to a large fetal size at birth.

The clinical importance of this phenomenon is that the size (but not growth rate) of babies in the first months of life is related more to their experiences during prenatal life than the height of their parents. Therefore, in a clinical assessment situation, we should not adjust an infant's height to the height of parents during the first years of life. When presented with a small baby, we should obtain information on its fetal growth, maternal health, maternal weight increment during pregnancy, drug intake, nutrition, and so forth. This information may greatly contribute to the understanding of the problem of small size of the patient during infancy.

Shifting Linear Growth During Infancy: An Example of Catch-up and Catch-down Growth

This observation is, to a certain extent, a direct consequence of the former concept. If phenotypically small babies can be born to genetically large parents and phenotypically large babies born to genetically small parents, then most of these children at some age must seek their respective centile related to their genetic size: They must acquire a canalized pattern of growth. If this is true, a considerable proportion of children must shift centile lines during the first 2 years of age. David Smith, an American professor of Pediatrics, confirmed this hypothesis in 1976.7 He found that approximately two thirds of normal infants shifted centiles upward or downward, achieving a new growth canal by 11-13 months of age. This means that, during the first 2 years of life, not all deviations of growth curves from the centile lines are necessarily abnormal. Size at birth of the child and parental size may help distinguish between normal and abnormal shifts. Velocity charts for weight increments in short periods of observation may also help (see later).

The process of shifting linear growth during infancy is an example of the catchup or catch-down growth that results in canalization. Catch-up and catch-down growth during infancy are special examples of the response of the child to the physical environment of the uterus. The former is in response to the constraining effect of a genetically large mother with a small uterus and the latter is in response to a genetically small mother with a large uterus.8,9

Mid-Childhood or Juvenile Growth Spurt

The plateau in growth velocity occurring between 5 and 10 years of age is interrupted between 6 and 8 years in both sexes by a growth spurt called the mid-growth or juvenile growth spurt. Although some authors claim that this spurt is present only in boys, others have found it to occur in both sexes at similar ages and mag-nitudes.10-12 This spurt is relatively small in linear dimensions, such as height, but is larger and more pronounced in dimensions relating to volume such as weight or skinfolds.

Figure 2-5, from the work of James Tanner and Noël Cameron on children in London, illustrates clear mid-growth spurts in calf circumference velocity in both boys and girls.12 Note that, although there is only a minor sex difference in the timing but not the magnitude of the mid-growth spurt, the subsequent adolescent growth spurt exhibits the usual enhanced sex difference, with boys being relatively delayed. Research by Swiss investigators has confirmed that the absence of sex differences in the mid-growth spurt and also that this spurt is uncorrelated with the timing or magnitude of the adolescent growth spurt, except that it occurs closer to adolescent growth spurt of the girls than the boys. The mid-growth spurt has been attributed to adrenarche characterized by an increase of the secretion of androgenic hormones of adrenal origin (see Chapter 5). This phenomenon coincides also with the appearance of axillary and pubic hair, secondary traits to those hormones.

figure 2-5 The mid-growth spurt in calf circumference velocity in London children. (Source: Tanner JM, Cameron N. Investigation of the mid-growth spurt in height, weight and limb circumferences in single-year velocity data from the London 1966-67 growth survey. Ann Hum Biol. 1980;7:565-577.)

the relevance of physical growth to pediatrics

Physical growth is an issue of paramount importance in pediatric practice. It is a central objective in child health programs, because the ultimate goals of such programs are not simply to reduce infant mortality but to provide the health care and environmental conditions to allow children to grow and develop normally to achieve their genetic potential as healthy adults.

Growth is also an instrument, for one of the most relevant actions to be taken in programs of child health surveillance is monitoring physical growth. It is also an excellent indicator of general child health and nutritional status. Some conditions can be recognized because the first clinical sign is growth delay, as sometimes happens with malnutrition, acquired hypothyroidism, and celiac disease. Hence, growth can be the first sign of an underlying disease in otherwise normal, asymptomatic children. One of the main general indicators and criteria of success used for the treatment and surveillance of chronic diseases is physical growth. Growth is also used in some cases to evaluate important therapeutic decisions in the surgical treatment of some conditions. For example, in some cases of surgical correction of gastroesophageal problems, physical growth of the operated child is an important indicator of success. Some drug treatments, such a steroids or immuno-suppressing agents, used in chronic diseases can affect physical growth; and their therapeutic benefits should be constantly balanced against their impact on growth and, of course, other secondary effects.

Physical growth is a relevant subject and a highly motivating issue for the parents; it enhances the communication among them, the pediatrician, and the rest of the health personnel, being an excellent central subject for the articulation of programs for health education to health professionals and to the community. All centers where children receive medical care should be provided with the appropriate personnel, anthropometric instruments, and growth charts for the proper assessment of physical growth in children.

Measurements of Clinical Importance

The three most important anthropometric measurements to be taken in pediatric practice are height, weight, and head circumference. These measure different components of the body, and their changes have different clinical and biological meaning.

Height

Height is a linear, unidimensional measurement. Although it mainly indicates the length of long bones of the lower limb (tibia, femur) and the irregular bones of the vertebral column, it is also an indirect indicator of the growth of the total lean body mass. In clinical pediatrics, changes in growth of height need a rather long period of observation to be detected (3 months or more), depending on the precision of the measurements. When growth in height is impaired, it can be assumed that an important health problem is present.

Weight

Weight is a three-dimensional measurement that includes both lean body mass and body fat. The relative proportions and distributions of lean and fat components depend on age, sex, and other environmental and genetic factors. Weight is a very sensitive measurement, in the sense that it can change from one day to another due to very minor alterations of body composition, for example, the changes seen in infants during a common cold. A change in weight does not tell us which particular tissue is being affected. Changes in body weight can be secondary to changes in body water (dehydration, overhydration), muscle mass (muscle hypertrophy by training, muscle atrophy), total lean body mass (wasting), fat (obesity, malnutrition), and so on. Weight changes can also be secondary to changes in body height, as it happens in growth retardation in stature or stunting.

Weight-Height Ratios

Some children have a low weight, not because they are lean but because they are very short, while others are heavy, not because they are obese but because they are very tall. This is a limitation to consider when we want to evaluate the amount of body fat as an indicator in nutritional assessment. One way to evaluate body fatness directly is by measuring subcutaneous fat using skinfolds. A way to do it indirectly is to evaluate weight in relation to height. A number of weight-height ratios exist, which use different power values. That most commonly used in pedi-atric practice is Quetelet's index, more commonly known as the body mass index (BMI). BMI is calculated from the formula BMI = weight/height2, where weight is in kilograms and height2 is in meters squared. Cutoff values for BMI describe obesity in both children and adults (see Chapter 18). In adulthood, a BMI greater than 25 kg/m2 is indicative of "overweight" and greater than 30 kg/m2 is indicative of "obesity." Childhood BMIs are much smaller than adult BMIs. The British BMI centiles developed by Cole, Freeman, and Preece13 show that BMI in childhood increases rapidly in the first year to peak at a 50th centile value of about 18 kg/m2. Deceleration follows until about 6 years of age, and then there is a steady increase until adulthood. The 50th centile BMIs in childhood (2-11 years of age) are less than 17 kg/m2 and during adolescence rise from 17 kg/m2 to about 22 kg/m2. BMI cutoffs for obesity, set at the 98th centile, are at a minimum of 18.5 kg/m2 at 5 years of age and then climb to 29 kg/m2 at 20 years of age. In addition to identifying overweight and obesity, BMI is also used to identify "wasting" or a low weight for height. Wasting is prevalent in developing countries where acute nutritional deprivation is registered by a lowered weight in relation to height.14,15

Head Circumference

Head circumference is the expression of growth of the brain; and its measurement is very important, especially during the first months of life, when it may be used to detect excess growth due to hydrocephaly. Congenital microcephaly can also be easily detected in infancy by measuring head circumference. Because of the rapid growth of the brain, head circumference increases relatively faster than height and weight in early years. At any given age, the brain is nearer its adult size than height and weight. At the age of 2 years, the brain, and therefore head circumference, have achieved nearly 80% their adult size, whereas height and weight have achieved only 50% the adult size. Because of this early rapid growth, head circumference is more liable to be affected by malnutrition or disease in the early years. Therefore, its importance for evaluating nutritional status in later childhood is diminished and seldom used on school-age samples.

These measurements should be performed in pediatric health centers with an adequate frequency, although it may vary according to available local resources. Weight and head circumference are recommended to be measured monthly during the first months of life, supine length should be measured every 3 months in this period. They can later be progressively spaced. Longitudinal studies of growth tend to be measured at 3-month intervals in the first 2 years, 6-month intervals to the start of adolescence, and every 3 months thereafter until adulthood (see Chapter 16).

growth problems in infancy and childhood Defining the Auxological Diagnosis

One of the most common causes of pitfalls in pediatric practice concerning the study of growth problems is the ambiguity in initially defining a growth problem. Failure in defining whether a child is too short, too light, or not growing at a normal velocity may be misleading with regard to further actions. The parents are usually very unspecific in stating the problem: They may say, "This child does not grow" when, in fact, they mean, "The child is too short" or "too light." These diagnoses are essentially different and have different clinical meaning.

In practice, when the clinician sees a child with an apparent growth problem he or she should ask two main questions:

1. Is this child's size normal for his or her age?

2. Is this child growing at a normal velocity for his or her age?

To answer the first question, the child should be appropriately measured and his or her height and weight plotted on appropriate distance charts, such as the one shown in Figure 2-6 for Argentinean children.16

The relative merits of international as opposed to national growth charts have been discussed on numerous occasions (see Chapter 18). The general consensus of opinion is that national charts, based on a selected sample of well-off children who have not been exposed to constraints on their growth, are appropriate as "standards" to reflect growth as it should be in the best possible circumstances within the chosen national environment (Figure 2-7). They are thus appropriate for the clinical monitoring of individual children. Currently available "reference charts" for international use include children from a variety of backgrounds and should be used to compare mean values for groups of children.17 If the height (or weight) falls within the centile lines, the child is classified as having a normal height or weight. The lower limit is generally set at the third centile, but this is a convention. The setting of a normal limit implies the assumption of a given sensitivity and specificity. Sensitivity is the power of detecting pathological cases; specificity is the power of recognizing normal cases. If we want a limit with a sensitivity greater than the third centile, we should then set the limit at an upper centile, for example,

figure 2-6 Argentine standard for height attained in boys. (Source: Lejarraga H, Orfila G. Estandares de peso y estatura para niñas y niños argentinos desde el nacimiento hasta la madurez. Arch Argent Ped. 1987;85:209-222.)

figure 2-6 Argentine standard for height attained in boys. (Source: Lejarraga H, Orfila G. Estandares de peso y estatura para niñas y niños argentinos desde el nacimiento hasta la madurez. Arch Argent Ped. 1987;85:209-222.)

the 10th centile. But this will be at the expense of reducing specificity. If, on the contrary, we want to increase specificity, then we should set a limit below the third centile, say at the first centile, but this, in turn, implies a reduction in sensitivity.

Post- term Age (weeks)

Post- term Age (weeks)

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