GROWTH AND DEVELOPMENT

•	Definition of growth.
•	Determinants of growth.
•	Periods of growth.
•	Assessment of growth.
•	Assessment of development.

Definition

1.	Growth:

a.	Increase in size of the body.

b.	Formation of new cells.

c.	Increase in the size and content of the cells.

2.	Development:

a.	Increase in complexity of an organ system or differentiation of form.

b.	Results in maturation of form and function.

Determinants of growth

1.	Genetic factors:

a.	Genetic background of individuals is the basis for the major determinant of growth potential: tall parents do tend to have tall children.

b.	Major genetic disturbances such as occur with chromosomal abnormalities often are reflected in growth patterns: e.g. 45XO Turner syndrome children have short statures.

c.	Many inherited genetic conditions can result in growth disturbance: skeletal dysplasias, e.g. achondroplasia.

2.	Nutritional factors

a.	Undernutrition: in utero or during postnatal periods, may affect both weight and height growth patterns and development of body organs.

b.	Overnutrition: lead to obesity with advanced linear growth and early pubertal maturation.

3.	Hormonal factors:

a.	Growth hormone: 

i.	increases protein synthesis, fat breakdown and hepatic glucose output and stimulates release of IGF-1 from the liver, together which stimulate bone and cartilage growth.

ii.	excess growth hormone leads to acromegaly; deficiency leads to dwarfism.

b.	Thyroid hormone: 

i.	promotes soft tissue growth and development of the nervous system.

ii.	deficiency causes profound growth and mental retardation.

c.	Testosterone: anabolic and growth promoting, responsible for adolescent growth spurt.

d.	Estrogens: in small doses may synergize with growth hormone to cause growth promotion; in higher doses will inhibit growth and promote early fusion of bony epiphyses.

Periods of growth

1.	Embryonic:

a.	Consists of the first 12 weeks of development in utero (1st trimester).

b.	1st week: germinal period, blastocyst formation and implantation.

c.	2nd week: bilaminar embryo with ectoderm and endoderm.

d.	3rd week: trilaminar embryo with mesoderm.

e.	4th – 12th week: formation and differentiation of major organ systems.

2.	Fetal:

a.	Consists of the 12th – 40th week.

b.	Most rapid phase of growth, characterized by rapid differentiation of body organs.

c.	Factors controlling fetal growth: placental supply of nutrients and oxygen and local growth factors, e.g. IGFd.

d.	Pituitary gonadotrophins regulate testicular testosterone synthesis in the male fetus, which is essential for normal development of the male phallus.

3.	Childhood:

a.	During the first years of life, linear growth velocity is rapid, e.g. average 8 – 12 cm / year, but plateaus through childhood to an average of 5 cm / year.

b.	The limbs grow faster than the trunk, so that the ratio of the upper to lower body segments diminishes from 1.7:1 during infancy to 1:! by age 10.

4.	Pubertal growth spurt:

a.	Puberty is associated with the onset of sex hormone production in boys and girls under the influence of the pulsatile release of gonadotrophins.

b.	Onset of puberty in:

	Boys	Girls	
Age	11	10.5 – 11	
Hormone	Testosterone	Estrogen	
Sign	Testicular enlargement	Breast development	
Followed by	Penile & scrotal growth.
Development of pubic & axillary hair.	Pubic & axillary hair growth.	

c.	In both sexes, the onset of puberty is followed by a peak linear growth velocity, at an average age of 12.5 years in girls and 14.5 years in boys.

d.	The sex hormones have direct effects at the skeletal growth plate, leading to fusion of the bony epiphyses and cessation of growth at an average age of 15 years in girls and 17 years in boys.

Assessment of physical growth

1.	Height:

a.	Reflects skeletal growth.

b.	Recumbent length:

i.	more accurate in the young, esp. < 2 years old.

ii.	child lies on a table with the measuring tape at the edge, with the soles are placed at the zero mark, and the movable bar at the vertex of the head.

c.	Standing height:

i.	convenient and most commonly used.

ii.	child stands barefoot with heels together and the head looking straight forwards (eye on the same level as the external auditory meatus), with heels, buttocks, upper back and occiput against the wall, and wooden head piece on the vertex.

d.	Upper segment-lower segment ratio (US:LS):

i.	LS: from pubic symphysis to growth, measures lower limb length.

ii.	US: height – LS, measures trunk length.

e.	Typical US:LS ratios:

Age	US: LS ratio	
Newborn	1.7:1	
1 year old	1.5:1	
5 years old	1.3:1	
8 years old	1.0:1	
Adult	0.9:1	

f.	Height age: age at which a child’s height would represent the 50th percentile.

g.	Mid-parental height:

i.	allows the height of any individual child to be considered in relation to the heights of his/her biological parents.

ii.	for boys: MPH = (F + M + 13.0) / 2

iii.	for girls: MPH = (M + F – 13.0) / 2

iv.	target range: target height + / - 7.0 cm for 10th – 90th percentile range.

2.	Height velocity:

a.	Reflects the child’s state at any particular time better than does the height attained.

b.	Based on sequential measurements taken at 3-monthly intervals over a period of 6 – 12 months.

c.	When measured over this time period, a normal child will tend to follow the same height percentile.

d.	A child with an organic or endocrine disease will tend to deviate away from the percentile line and may move downwards across the percentile lines.

e.	Decreases from birth onwards and is interrupted by the adolescent growth spurt.

f.	Typical height patterns:

Age	Height gained	
Newborn	50 cm	
1st year	25 cm	
2nd year	12.5 cm	
3rd year to adolescence	6 cm / year	
Puberty	Girls: 8.5 cm / year
Boys: 9.5 cm / year	

3.	Weight:

a.	Reflects the composite growth of all tissues and is therefore less useful in the long-run.

b.	Parameters of measurement:

i.	weight.

ii.	weight for height charts.

iii.	body mass index.

c.	Typical weight pattern:

i.	birth weight regained by 10 – 14 days.

ii.	average weight gain of 20 – 30 g / day for the first 6 months and 15 g / day for the next 6 months.

iii.	doubles birth weight by 4 months.

iv.	triples birth weight by 1 year.

v.	quadruples birth weight by 2 years.

4.	Occipitofrontal circumference:

a.	Reflection of brain growth.

b.	Measuring tape over the glabella/supraorbital ridge and the occiput.

c.	Compare with relation to height and weight.

d.	Typical growth pattern:

i.	newborn: 34 – 35cm

ii.	6, 3, 2, 1cm for each quarter of the first year.

e.	Closure of fontanelles:

i.	anterior fontanelle: 9 – 18 months.

ii.	posterior fontanelle: 4 months.

5.	Skin fold thickness:

a.	Measure of subcutaneous fat and obesity.

b.	Measure triceps or subscapular skin fold thickness with Harpenden calipers (can also use nape of the neck, flank and medial thigh).

c.	Girls have more subcutaneous fat than boys.

d.	Fat deposition increases till 9 months of age, then decreases, and increases at 6 – 8 years of age again.

6.	Percentile charts:

a.	These charts demonstrate the range of normal growth, expressed either as percentiles or as standard deviations (SD) from the mean for age.

b.	The percentile curves are derived from the overall distribution of the data.

c.	The normal range of average height or weight on the charts falls between the 3rd and 97th percentiles.

Assessment of development

1.	Clinical development assessment

a.	Principles:

i.	cephalocaudal direction.

ii.	generalized mass activity is replaced by specific individual responses.

iii.	certain primitive reflexes must be lost before the corresponding voluntary movement is acquired.

b.	Aspects:

i.	gross motor: sitting, crawling, standing, walking, prone, ventral suspension.

ii.	fine motor: grasp.

iii.	vision.

iv.	hearing: localizing sounds.

v.	speech: babbling, monosyllables, phrases and sentences.

vi.	social: stranger anxiety, feeding, dressing, continence.

vii.	appropriate primitive reflexes.

2.	Bone age

a.	Bone age is an index of physiological maturity, indicating the state of bony epiphysial maturation.

b.	It reflects the stage of development better than chronological age.

c.	Assessment of bone age by:

i.	number and size of epiphyseal centers.

ii.	size, shape and density of the outlines of the bony ends.

iii.	distance of separate epiphyseal centers from zone of provisional calcification / degree of fusion.

d.	The bone age indicates the average age of children at a similar stage of bony maturation and is a guide to the remaining growth potential of the child.

e.	In normal children the bone age can be delayed up to 2 years behind the chronological age, but is rarely advanced a year beyond the chronological age.

f.	Bone age is obtained by performing an X-ray of the left wrist (for children up to 12 years) or of the knees and ankles (in neonates).

g.	Use of bone age:

Growth problem	CA	HA	BA	
Genetic short stature	10	HA < CA	BA = CA	
Constitutional delay	10	HA < CA	BA < CA
BA = HA	
Delayed puberty	15	HA < CA	BA < CA	
Precocious puberty	6	HA > CA	BA > CA	

CA: chronological age. HA: height age. BA: bone age.

3.	Pubertal staging

a.	Tanner’s sex maturity staging.

b.	Girls: breast tissue and pubic hair distribution.

c.	Boys: volume of testis/penile length and pubic hair distribution.

d.	Female pubertal changes start 8 – 13 years, while male pubertal changes start at 9.5 – 13.5 years.

e.	Breast development and testicular enlargement are the first signs of puberty in girls and boys respectively.

4.	Dental maturity:

a.	Deciduous dentition erupts from 6 months to 2 years, beginning with the lower central incisors, the upper central incisors, the upper lateral and the lower lateral incisors, and finally the first molars and canines.

b.	Permanent dentition erupts from 6 years to 13 years.

c.	3rd molars erupt much later.

d.	Delayed dentition may be a sign of disease, e.g. hypothyroidism, malnutrition and rickets.