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  » Baby's developmental milestones  »  Growth and Development In Infants
INTRODUCTION

Growth is an essential feature of a child. This distinguishes him or her from an adult. The process of growth starts from fertilization of the Ovum and continues until the child grows into a fully matured adult. During early Embrionic period of life, an exponential increase of the number of dividing cells occurs. The number of cells increases from about 0.2x10x12 at 60 days of fetal life to 2x10x12 at birth and 6x10x13 in afully grown adult. This is evidenced by an increase in the DNA content of tissues. At the early Embrionic stage, fetal cells differentiate to form tissues and organs.
In the latter half of pregnancy and early childhood, there is also an increase in the cell size. This manifests as an increase in the Protein:DNA ratio. The cell size continues to increase till 10-11yrs of age. After that, increase in cell size occurs more slowly. The body cells remain in a state of dynamic equilibrium, so that ageing cells are continuously replaced, with new ones. However the rate of turnover of cells in different tissues varies.
The terms of growth and development, are often used together. These are not interchangeable, for they represent two distinct facets of the dynamics of change, ie, those of quantity nad quality. Growth and development usually occur concurrently. But may not be interrelated.
The term GROWTH, denotes a net increase in the size or mass of tissues. It is largely attributed to multiplication of cells and in an increases of intracellular substance. Hypertrophy or expansion of cell size, contributes to a lesser extent to the process of growth.
DEVELOPMENT, specifies maturation of functions. It is related to the maturation or myelination of the nervous system and indicates the acquisition of skills for optimum function of the individual.

FACTORS AFFECTING GROWTH AND DEVELOPMENT

GENETIC FACTORS:

a) Phenotype-The parental traits are usually transmitted to the offspring. Thus, tall parents usually have tall children and kids of short parents usually tend to be short in height. The size of the head is more closely related to that of the parents than are the size and shape of the hands and feet. Similarly, the structure of the chest and fatty tissues have better genetic association than other somatic characteristics.

b) CHARACTERISTICS OF PARENTS: Parents with high IQ(Intelligent quotients) are more likely to have children with higher levels of inherited intelligence. This is further enhanced because of the greater degree of environmental stimulation in such homes. Children of certified mentally subnormal mothers, generally have a lower IQ than the average but the outlook is not as gloomy as is was once thought.

c) RACE: Growth potential of different racial groups is variable when taking in socially and environmental factors.

d) SEX: Boys are normally longer and heavier than girls at birth. At the age of one year there is no appreciable difference in their length and weight in relation to sex. Although the pubertal growth spurt occurs earlier in girls, their mean height and weight are usually less than boys of corresponding ages at the time of full maturity.

e) BIORHYTHM AND MATURATION: Daughters often reach menarche at a similar age as their mothers did. They may have similar length of their menstrual cycle.

f) GENETIC DISORDERS: Growth and development are adversely affected by certain genetic disorders.The latter may be of two types, viz,.
I)Chromosomal abnormalities and
II)Gene mutations.
CHROMOSOMAL ABNORMALITIES-Several chromosomal defects manifest themselves as severe growth disturbances.These include Turners Syndrome(45 Chromosomes:one X chromosome missing) and Downs Syndrome(47 chromosomes with trisomy of number 21).
GENE MUTATION- Mutation of a single or multiple genes may result in inherited disorders of growth. Major metabolic defects, are known is some of these, eg, mucopolysacchariodosis and galactosemia, etc.The precise biochemical abnormalities in the vast number of inherited genetic mutations may not be easily identifiable.

g)Children of multiple pregnancies: Ultimate growth of these children is related to the difference in birth weight of twins. Smaller new borns are more likely to attain lower height and weight when compared to their heavier siblings.

ENVIROMENTAL FACTORS

PRENATAL PERIOD:

The fetus grows in the maternal enviromant in utero. Thus the protoplasm of the ovum and that part of the genome of the mother which is not transmitted to the fetus, but which, nevertheless, is present in the maternal tissues(where the embryo is growing) influence the fetal growth.This probably explains why the progeny usually shows greater similarity to the mother in respect of somatic development, physiological and biochemical maturation. Maternal malnutrition is identified with intrauterine growth retardation and consequently small size of the fetus. Medical illnesses of the mother before and particularly during the first trimister pregnancy and certain infections (maternal Rubella-results in cardiac abnormalities for the fetus and their growth in utero and after birth is not optimal,syphilis, viral diseases such as cytomegalic inclusion disease, Toxoplasmosis, etc may be transmitted to the fetus and thus arrest or retard fetal development and result is various organ abnormalities)also result in poor growth of the fetus. Average birth weight of babies born to mothers receiving nutritional supplements during their antenatal period, are higher than in those left to fend for themselves, without supplements.

Administration of some drugs, eg, Thalidomide to the pregnant mother during the first trimester (first three moths)adversely affects the differentiation and development of those organs differentiating at that stage of pregnancy, ie, limbs, resulting in Phocomelia(ie. Short, malformed, seal like, limbs)

HORMONAL INFLUENCES ON GROWTH:

a) THYROXINE-Human fetus secretes Thyroxine from the 12th week of gestation onwards.Its secretion is dependant on the plasma Thyriod Stimulating Hormone(T.S.H).Thyroxine does not affect the linear growth of the fetus in utero, but it significantly retards the skeletal maturation of the fetus. Birth weight may be below or above normal due to the accumulation of myxedematous fluid. Maternal Myxedema results in fetal hypothyroidism. Administration of antithyroid drugs and iodides to the mother during pregnancy, particularly the latter part may result in fetal goiter and hypothyroidims and retardation both mentally and physically(Cretinism).

b) INSULIN-Insulin stimulates fetal growth. In mothers with latent or overt Diabetes, the fetus is usually excessively large and with excessive birth weight ie usually, over 5kgs or nearabouts.As the maternal blood sugar is high this results in elevated fetal blood levels. This leads to hyperplasia of the islet cells of the fetal pancreas.

c) GROWTH HORMONE-Fetal growth hormone is probably not essential for fetal growth in utero.This is probably regulated by the maternal Human Chorionic Gonadotrophin hormone.

POSTNATAL PERIOD

Enviromental experiences of the child during postnatal life determine the pace and pattern of growth and development. These factors include: a) the nutritional status, b) exposure to toxic chemical agents, c) trauma, d) residua of infections, e) maternal metabolic disorders, f) social, g) emotional and, h) cultural factors.

a) Nutrition-Growth of children suffering from protein calorie malnutrition(P.C.M.), anaemia and vitamin deficiency states is retarded. Overeating and obesity, accelerate somatic growth.

b) Chemical agents-Administration of androgenic hormones initially accelerates skeletal growth but ultimately epiphyses of bones close prematurely and therefore bone growth, in such cases ceases relatively early. Final height in such individuals is stunted, though muscular and reach sexual maturity before the normal.

c) Trauma-Head injury may result in serious mental retardation and spasticity. Fractures, through the growth epiphysis of the long bones, may result in damage to the epiphysis and resulting in unilateral short limbs.

d)Infections and infestations- Systemic infections and parasitic infestations usually decrease the velocity of growth.This factor may be the cause why children born in developing countries (third world) usually have an ultimate shorter stature than similar socioeconomically brought up children in the so called 'developed countries' of the world.

e) Social factors:
I) Socioeconomic level: Children from families with high socioeconomic levels usually have superior nutritional status and suffer from fewer infections than those of lower stratar of society and are thus taller and more mentally well developed.
II) Climate:The velocity of growth may alter during different seasons and is usually higher in spring and low in summer months. Infections and infestation is more common in hot and dusty, humid, summer months. Weather has also a pivotal role to do with food production and thus the nutritional status of the growing child.

f) Emotional factors-Children from broken homes and orphanages do not grow as well as similar children from secure families taking into similar nutritional status factors.Anxiety,insecurity, lack of emotional support and love from the family, prejudice the normal neurochemical regulation of secretion of Growth hormone. Parents who had a happy childhood, are more likely to have children with a cheerful, happy healthy countenance.

g) Cultural Factors-Superstitions,culturally routed methods of deliveries, child rearing, infant feeding in the community are determined by cultural habits and norms.There may be religious taboos against consumption of certain foodstuffs, eg, vegetarianism, in a economically and socially backward enviroment with little hope of exposure to different vegetables throughout the year. These affect the nutritional state and growth performance of children. Daughters are sometimes thought as burdens on an already heavily burdened family budget (in some Asian countries, the families of girls, have to pay exorbitant dowries, so as to get married-sons are said to bring in the wealth), so are ill treated and second to the male members of the family, both nutritionally, emotionally deprived and educationally backward, than their brothers, in the same family environment. Thank God, with education,the situation is changing slowly but surely for the better, in such countries.


PERIODS OF GROWTH

Prenatal period
Ovum 0 to 14 days
Embryo 14 days to 9 weeks
Fetus 9 week to birth
Perinatal period 28 weeks of gestation to 7 days after birth
Postnatal period
New born First 4 weeks after birth
Infancy First year
Toddler 1 to 3 years
Prescool child 3 to 6 years
(In some studies children under 5 years are classified as preschool children)
School age child 6 to 10 years (girls)
6 to 12 years (boys)
Adolescence
Prepubescent 10 to 12 years (girls)
12 to 14 years (boys)
Pubescent 12 to 14 years (girls)
14 to 16 years (boys)
Postpubescent 14 to 18 years (girls)
16 to 20 years (boys)