Growth, childhood

The increase in height and weight as a child develops. The period of most rapid growth occurs before birth. After birth, although growth is still rapid in the first few years of life, especially in the first year, the rate of growth steadily decreases. Puberty marks another major period of growth, which continues until adult height and weight are reached, usually at about age 16–17 in girls and 19–21 in boys. Body shape changes during childhood because different areas grow at different rates. For example, at birth, the head is already about three quarters of its adult size; it grows to almost full size during the first year. Thereafter, it becomes proportionately smaller because the body grows at a much faster rate. Growth can be influenced by heredity and by environmental factors such as nutrition and general health. Hormones also play an important role, particularly growth hormone, thyroid hormones, and, at puberty, the sex hormones. A chronic illness, such as cystic fibrosis, may retard growth. Even a minor illness can slow growth briefly, although the growth rate usually catches up when the child recovers. In some cases, slow growth may be the only sign that a child is ill or malnourished, in which case it is known as failure to thrive. However, short stature does not necessarily indicate poor health. Abnormally rapid growth is rare. Usually, it is a familial trait, but it may occasionally indicate an underlying disorder, such as a pituitary gland tumour causing gigantism. (See also age; child development.)