Pattern of development during babyhood weight
At the age of four months, the baby's weight has normally doubled. At one year, babies weigh, on the average, three times as much as they did at birth, or approximately 10 kgs. Increase in weight during the babyhood comes mainly from an increase in fat tissue.
At 4 months, the baby measures between 23 and 24 inches, at one year, between 28 and 30 inches and at two years between 32 and 34 inches.
Head growth slows down in babyhood while trunk and limb growth increases. Thus the baby gradually becomes less top-heavy and appears more slender and less chubby by the end of babyhood.
The number of bones increases during babyhood. Calcifications begins in the early part of the first year but is not completed until puberty. The soft spot on the skull or fontanel has closed in approximately 50% of all babies by the age of 19 months and almost all babies by the age of two years.
Muscle fibres are present at birth but in very under developed forms. They grow slowly during babyhood and are weak. By contrast, fat tissue develops rapidly during babyhood, due partly to the high fat content of milk, the main ingredient in a baby's diet.
During the second year of life, as body proportions change, babies begin to show tendencies toward characteristic body builds. The three most common forms of body build are ectomorphic, which tends to be long and slender, endomorphic, which tends to be round and fat, and mesomorphic which tends to be heavy, hard and rectangular.
The average baby has four to six of the twenty temporary teeth by age of one and sixteen by the age of two. The first teeth to cut through are those in the front, the last to appear are the molars. The last four of the temporary teeth usually erupt during the first year of early childhood.
At birth, brain weight is one-eighth of the baby's total weight. Gain in brain weight is greatest during the first two years of life, thus accounting for the baby's top-heavy appearance. The cerebellum, which plays an important role in body balance and postural control, triples in weight during the first year of postnatal life. This is true also for the cerebrum. Immature cells, present at birth, continue to develop after birth but relatively few new cells are formed.
By the age of three months, the eye muscles are well-enough coordinated to enable babies to see things clearly and distinctly and the cones are well-enough developed to enable them to see colors. Hearing develops rapidly during this time. Smell and taste, which are well developed at birth, continue to improve during babyhood. Babies are highly responsive to all skin stimuli because of the thin texture of their skin and because all sense organs relating to touch, pressure, pain, and temperature are present in well-developed forms.