Infant growth and development

Infant growth and development are the main theme of a baby's life. It is through this process that that a newborn ends up becoming a toddler and then a child, and it is growth and development in childhood and through puberty, that usher that individual into adulthood. There are two stages in life when growth and development are most rapid and profound, one is in infancy and early childhood, and the other is during puberty and adolescence. Although there are short periods during any stage when a child is mainly getting bigger; infancy, childhood and adolescence are not focused on a mere increase in size.

The proportions and shape of the body change, and the relative size and physiology of many organs do, as well. A series of neurologic and behavioral changes occur in all babies, regardless of specific culture or ethnicity, that are vital in growth and development.

Human beings, as a species, have a pair of apparently unrelated characteristics that greatly influence the starting and end points of this process: a large brain that is capable of a high intelligence, and an upright body position that is propelled by walking on two legs. That means that big headed babies are born to mothers with pelvic structures adapted to walking upright, and if both mother and baby are to survive the birth process, that means the baby's brain is not fully developed in size -or complexity, at birth. No matter how precocious we may fancy that our children are, no human baby is precocious in the same sense as a horse's newborn foal or a duckling just out of the egg- unlike these newborns, that can run and swim, humans are unable to do much more than feed and interact with their caregivers until several months of life have passed.

Our newborns have a skull that contains a brain case only one quarter the size that it will become in the adult. Much of the growth of the brain -and the concommittent expansion of the head, has occurred by the age of 2 years - at that age the neurocranium (which means the bony skull that surrounds the brain) is 75% of the adult size. By about 10 years of age, the brain (and skull) are aproximately 95% their ultimate size. Overall, the human brain more than triples in size (3.5 X) from birth to adulthood.

Even with the relatively small head diameter of the newborn, that skull has some adaptations that allow it to be molded in the birth canal, so that the diameter can become even smaller and spare harm to the mother. These same adaptations give the baby's skull the ability to expand to accomodate the growing brain. They are the suture lines and fontanelles of the infant skull.

When babies are brought to the pediatrician or other health care provider for well-child care, the infant's length, weight, and head circumference are routinely measured. The baby is also checked for reflexes and activities that are the signs of normal physical and mental progress. Although the rate of change is a bit different for each individual child, this article reviews the important characteristics, and their timing, of an infant's first years of life. Strictly, that term "infant" only applies to baby during the first year- but since such activities as walking can normally occur either during that first year - or after- a broader range of ages is considered here.

Newborns

A newborn baby has

Changes in the body that come from activities

Body parts are not static structures, they change depending on how they are used. Bone will pout out where it is attached to muscle, and the muscle pulls on the bony process that gives rise to it. For example, the mastoid process, which is the thick bump that can be felt behind any adult's ear (down around the region of the upper earlobe), does not exist as a bump in the newborn baby. The baby's skull is flat behind the ear. A muscle in the neck, the sternocleidomastoid muscle, runs, in part, from this spot on the skull, down to the collar bone and the top of the sternum. As the muscle contracts with the greater force as the baby grows and developes the ability to raise his head and hold it up, the bone actually thickens and the mastoid process developes. Other changes in the body occur with standing and walking. The spine developes what is called "lordosis", the straight backed baby has a different back contour than the walking toddler. The bottom of the feet in the baby who does not stand are "rocker-bottom" shape, and change as the child puts weight on those feet and change still more with walking. In those disabled children who never walk , the feet retain their infant contour.