6 Catch Up Growth, Maturation , Growth References And Standards

Ms. Urvashi Gupta and Dr. Meenal Dhall

Contents of this unit

1. Introduction

2. Catch-up Growth

2.1 Compensatory Growth

2.2 Canalization

2.3 Catch-up growth in association with Canalization

2.4 Factors affecting catch-up growth

2.4.1 Malnutrition

2.4.2 Celiac Disease

2.4.3 GH Deficiency

2.4.4 Hypothyroidism

2.4.5 Intra-uterine Growth Retardation

3. Maturation

4. Growth References and Standards

5. References

Learning Outcomes

• To understand the concept of catch-up growth
• To have clear understanding of related topics like canalization and compensatory growth
• To know about the factors affecting catch-up growth
• To know about growth standards and references

1. Introduction

According to British English dictionary, growth refers to the progressive development of a living being or part from an earlier stage to its maturity including increase in size and development as a series of changes by which an individual embryo becomes a mature organism.

Many times, people use the terms growth and development interchangeably without realizing that these terms actually differ in their meanings. In Biological and Physiological sciences, these terms have slightly differing connotations. Growth refers to increase in size of various organs and parts of body by multiplication of cells and intercellular components during a period commencing from fertilization to maturity. Growth is actually a result of three processes – increase in cell number (hyperplasia), increase in cell size (hypertrophy) and increase in inter-cellular substances (accretion), which underlie maturity and differentiation. Development or maturation is the increase in functional capacity for producing specialized cells from unspecialized ones and complexity in skill progression. Therefore, growth is increase in terms of quantity while development in terms of quality. Both are target seeking and dynamic in nature. The end point of growth is size attainment by adulthood at a rate less than 1cm/year. The end point of maturity is the functional ability of an individual to procreate and not simply be able to produce viable sperms/ova. Thus, successful maturation requires not just biological but also behavioral and social maturity (Cameron, 2012).

Growth remains the chief phase of biological activity up to about 20 years of age, whereby height, weight, body build, etc of a person increase till he reaches his adult age and afterwards sooner or later starts degenerating too, marking the beginning of older/senescence age. However, the rate at which these changes take place differ in different stages of growth. For example, during prenatal, neonatal, infancy and adulthood, growth rate increases very rapidly. It slows down during infancy and gets stable during adulthood. However, during old age, cells and tissues start degenerating. These processes are highly influenced by both genetic (intrinsic) and environmental (extrinsic) factors including release of endocrine and exocrine hormones, especially growth hormone, genetic aberrations, Epigenetics, nutrition, season, climate, altitude, socio-economic condition, psychological condition, race and ethnicity. In case, any of these factors are not available or becomes unsuitable, it would hamper the proper growth and development of the individual.

Assessment of growth and maturation depends upon various indicators. While dealing with huge data to come up with the outcomes revealing the trends and patterns of growth, it becomes important to have certain reference with which the collected numbers could be related and compared. These standards and references must be universal, sequential, reliable, valid and complete in terms of their characterization of maturity. Considering this, several standards and references are set up at national and international levels allowing the comparison of various groups of people inhabiting different regions of world.

2. Catch-up Growth

The term catch-up growth was introduced by A. Prader, J.M. Tanner and G.A. Von Harnack (1963) to describe the increased growth velocity which occurs in children after a period of growth retardation when the cause of the growth retardation is removed (Cameron, 2012). It is the growth velocity above the statistical limits of normality for a particular age during a defined period of time, following a transient phase of growth inhibition (Boersma, et al., 1997). After illness or starvation which is a period characterized by slow growth, there has been found tendency in the younger subject’s to bridge the deficit as soon as possible and catch up with the original growth-curve. This is known as catch-up growth. The velocity during initial period of catch-up may reach three times the normal for age. The term compensatory growth is sometimes used by nutritionists to describe a similar phenomenon; however, that term was first applied to the quite different phenomenon of the replacement growth of organs or parts thus, showing compensatory growth. Catch-up may be complete or incomplete; if the stress has been severe, and particularly if it has been applied early in the animal’s life, then even though a catch-up velocity may be established for a while it may be insufficient to return the animal completely to its normal curve of growth (Bose. K). The end point of catch-up growth is to take an organism towards, or in favorable circumstances right onto its original pre-retardation growth curve. In the former case, catch-up growth is said to be incomplete and complete in the latter.

2.1 Compensatory Growth

Catch up growth and compensatory growth appear to synonymous, but they are not. Compensatory growth is not only used to describe the growth of whole organism but also the overgrowth of a single or part of an organ when another part is removed. For example regeneration of liver either after its partial hepactomy or due to removal of its part for purpose like organ transplantation/donation. Hence, compensatory growth could actually be the effort of an organ or its part to overcome the effect of some functional inadequacy. For achieving this, the remaining part/cells of the organ undergo the basic processes of growth- hyperplasia, hypertrophy and accretion. In other words, it is a type of growth that occurs mainly after the loss of a mass of cells/tissues or part of an organ itself. Compensatory growth may be viewed as being controlled by a simple feedback mechanism while catch up growth is rapid growth that compensates for the loss of potential tissues and thus can’t be accounted for by a simple feedback mechanism. Mechanism controlling catch-up growth must be able to foresee lack of growth response of a tissue while the mechanism for checking compensatory growth reacts to the permanent loss of a tissue (Boersma et al., 1997).

2.2 Canalization

Canalization is the tendency of a trait to follow a certain course or trajectory over time. Growth being a dominant biological activity from prenatal phase till the attainment of adulthood, leads to many physical and biological changes in an organism. Rapid growth during infancy which slows down throughout childhood, suddenly increase again at adolescence and puberty, which then finally ceases at adulthood. This cyclic and periodic acceleration and deceleration of growth during different phases needs some mechanism to keep a check on it. Such a controlling system is very dynamic and complex that makes the growing child return to its path of growth after deviation. This tendency to keep to a narrow and predictable track of growth is called canalization. It is a pre-requisite for catch-up growth. If normal growth is not canalized then it would not be possible to recognize the phase of catch-up growth. Canalization is the individual growth curve that parallels the centile curves of growth charts.

In the pre-pubertal period, canalization is clearly recognizable, but thereafter its presence becomes less pronounced. Hence, catch-up growth spurt is easily recognizable in the pre-pubertal period, and ther after it is often impossible to discriminate between pubertal growth spurt and catch-up growth acceleration (Boersma, et al., 1997).

The term canalization was first used by C.H. Waddington in 1957 to describe the pattern of growth in all children that is more or less parallel to a particular centile or with some imaginary canal in an environment that does not constrain their growth. It is most likely that this pattern is genetically determined and a target seeking phenomenon whose main aim is to take an individual to the adult stature in an unconstrained environment.

2.3 Catch-up growth in association with Canalization

No child can ever be brought up in a completely unconstrained environment. Even towards the end of our intra-uterine life, our growth was constrained by the size of the uterus. During infancy and childhood, children are all the time vulnerable to various diseases. Diseases which can lead to loss of appetite thus hampering and slowing down the rate of growth or in more severe case may actually cease it.

While explaining the concept of canalization and catch-up growth, Waddington compared growth with movement of a ball rolling down a valley. Here, different phases of catch-up growth have been related to different points of the ball’s movement.

• Movement of the ball down the valley on a central course, is the first phase representing the canalized growth, where the sides of the valley keeps the ball on the right track and helps it to roll steadily. This is point A of the ball’s movement.
• In case of an obstacle, the ball tends to move out of its regular path or canal, which pushes the ball to move away from the central path. It represents point B or the second phase in which an insult causes the normal growth to get slow down or changing its actual rate and path.
• The amount of deviation from the predefined path depends upon the severity and duration of the insult. Likewise, the velocity of the moving ball depends upon the severity and duration of the obstruction coming in its path. When the obstacle is removed, the ball tends to return to its original path maintaining its initial velocity or it just move with a much faster speed down the valley. This is the point C which resembles the third phase of catch-up growth when the insult is alleviated and the rate of growth resumes its normal speed or gets doubled.
• At point D, the ball acquires its earlier path of the valley and so does the growth which resumes its normal canalized path in the last phase of the catch-up growth.

2.4 Factors affecting catch-up growth

It is not in all cases that catch-up growth takes place and resumes the normal growth of a person. In several cases, the severity or duration of the insult is so much that catch-up growth is never able growth to turn up and the growth rate is never able to return to its original pace, resulting in permanent stunting of growth. Therefore, the harshness and the longevity of the constrained environment drive the movement of catch-up growth. Some of the cases have been discussed below to explain the response of catch-up growth in each of them.

2.4.1 Malnutrition

It is the most common cause of stunted growth and under-development. Prolonged malnourishment results in permanent stunting and growth inhibition. However, severity of undernourishment results in the faster pace of regaining the growth rate. Whereas, under nutrition in the initial stages of life may have very harmful effects on the growth of a child, leading to slow growth initially and later leading to under-development.

2.4.2 Celiac Disease

It is a kind of abnormality in which the gut lining inhibits the absorption of food, resulting in the child being starved. Since it causes malabsorption, growth retardation in the initial stages of growth is witnessed leading to breakdown of normal linear growth and short stature.

2.4.3 GH Deficiency

Insufficient production of growth hormone in the body is another one of the common factors responsible for stunted growth and growth retardation, especially in the younger ages.

2.4.4 Hypothyroidism

It is associated with growth failure due to decreasing effects of the thyroid hormones on the skeletal growth. It also leads to a secondary reduction in the release of GH. However, it treated properly, at right time; the growth rate can pursue its original rate ensuring positive catch-up growth.

2.4.5 Intra-uterine growth retardation (IUGR)

It is diagnosed when the birth weight or birth length is lower for the gestational age of the infant. Major proportion of children with IUGR tends to attain catch-up growth in the first two years of their life. However, 20-30% of IUGR affected children are not able to catch-up at all and remain underdeveloped. The probability of catching up completely depends upon the damaging agent, its timing of occurrence and the duration of damage.

3. Maturation

Bogin defines maturation or development as “a progression of changes, either qualitative or quantitative, that lead from an undifferentiated or immature state to a highly organized, specialized and mature state”. The end point of maturation, within the context of growth, is the attainment of adulthood, which is the state of being a functionally mature individual. Functional maturation, in the biological context, implies to the ability to successfully procreate and raise offspring who themselves will successfully procreate. The process of maturation continues throughout life-it begins at conception and ends at death. Thus, growth and maturation are closely related and both must reach functional and structural endpoints for providing the opportunity of successful procreation (Cameron, 2012).

Maturation is not linked to time in a chronological sense. In other words, one year of chronological time is not equivalent to one year of maturational time. Although, each individual has passed through the same chronological time span, but that doesn’t mean that they would have same rates of maturation. Maturation is often assessed by the identification of maturity indicators that are discrete events or stages recognizable within the continuous changes that occur during the process of maturation. There is variability of maturation within an individual, meaning that two events are not mutually related or associated.

Maturation could be assessed using the following indicators:

• Skeletal maturity
• Dental maturity
• Sexual maturity in terms of development of secondary sexual characteristics among both males and females

4. Growth References and Standards

Growth references and standards are essential components in the human growth and development studies. Their value resides in helping to determine the degree to which physiological needs for growth and development are met during the important childhood period. Beyond their usefulness in assessing children’s nutritional status, many governmental and United Nations agencies rely on them to measure the general well-being of populations, formulate health and related policies, and plan interventions and monitor their effectiveness. Growth Standards and references describe the standards for constructing following charts-length/height-for-age, weight-for-age, weight-for length, weight-for-height and BMI-for-age. The construction of the child growth curves requires a careful, methodical process. Rigorous methods of data collection and standardization are followed during the entire study. Sound

Procedures for data management and cleaning are applied. As a result, the anthropometric data available for analysis become of the highest possible quality. The selection of the best statistical approach to construct the standards follows a broad consultative process (WHO).

A growth reference aims to describe the growth pattern in a population. It aims to prescribe what the normal growth pattern should be. In order to prescribe, it is important that growth standards are based on data from people without known risk of growth faltering. For example: the WHO growth standards excluded not only infants with mortality but also infants whose mothers did not follow recommended breastfeeding and non-smoking guidelines (Cheung, Y.B.).

A growth reference is a table or chart summarizing how an anthropometric measurement such as height, weight, etc changes during childhood, based on a defined reference sample and the charts consist of selected centiles of the measurement at different ages of childhood. Purpose of growth reference is to account for age and sex differences in anthropometry. In practice it is used in two contexts: as clinical sign, to monitor the growth status of individual children, and as a public health tool, to summarize and compare the anthropometry of groups of children. On the other hand, growth standard represents healthy growth, whereas reference makes no claims about the health of its reference samples. Therefore, a standard is better than a reference for diagnosing the growth disorders, always assuming that the standard is appropriate for the child being assessed. In practice reference is easier than a standard to construct, as there is no need to define good growth, or to exclude individuals from the reference sample who fail to achieve it (Ulijaszek et al., 1997).

Summary

The biological phenomenon of Catch-up growth is a strong inherent will and power of a child to resume and maintain its predetermined growth pattern. The Multifactorial nature of catch-up growth is revealed by the fact that not only among different diseases but also among different individuals with the same disease, variability in following up catch-up growth has been witnessed and supported through various studies conducted in different parts of the world. Apart from nature-nurture (gene-environment) effects on the pattern of catch-up growth among different individuals in different settings, the intensity, duration and, the time and type of insult hampering the growth of individual along with the efficacy of the treatment or therapy provided and the time at which it is being provide (for example, such a treatment would have maximum positive influence on growth pattern if provided at the initial stage of exposure to the insult, while it would have minimum effect if provided afterwards when there are no further chances of improving the growth) represent the major influencing factors.

Maturation, being a progression of changes that lead from an undifferentiated or immature state to a highly organized, specialized and mature state, results in the functional maturity of an individual. In the biological context, it refers to the ability to successfully procreate and raise offspring who themselves will successfully procreate. It is not a strictly time/chronological age dependent process hence, two individuals of the same age may not have the same level of physical maturation changes. Moreover, not even two maturation events are synchronized to happen in the same individual. Therefore, there are methods for assessing the level of maturation using certain physical features or indicators- skeletal maturity, dental maturity and sexual maturity in terms of development of secondary sexual characteristics among both males and females.

Growth references and standards are essential components in the human growth and development studies. Their significance lies in the fact that they are really very useful in assessing children’s nutritional status. Many governmental and United Nations agencies rely on them to measure the general well-being of populations, formulate health and related policies, and plan interventions and monitor their effectiveness. For constructing following charts-length/height-for-age, weight-for-age, weight-for length, weight-for-height and BMI-for-age, growth references and standards play very important role as they determine the degree to which physiological needs for growth and development are met during the important childhood period.