Puberty

The physical changes that occur at puberty are regulated by changes in levels of hormones that are produced by the pituitary gland--luteinizing hormone and follicle-stimulating hormone. At birth, the levels of these hormones are high, but they decrease within a few months and remain low until puberty. Early in puberty, levels of luteinizing hormone and follicle-stimulating hormone increase, stimulating the production of sex hormones. The increased levels of sex hormones result in physical changes, including maturation of the breasts, ovaries, uterus, and vagina. Normally, these changes occur sequentially during puberty, resulting in sexual maturity (see Section 23, Chapter 270).

The first change of puberty is usually the start of breast development (breast budding). In girls who live in the United States, this change usually occurs around age 9 to 11. Shortly afterward, pubic and underarm hair begin to grow. The interval from breast budding to the first menstrual period is usually about 2½ years. In the United States, girls, on average, have their first period when they are almost 13. The girl's body shape changes, and the percentage of body fat increases. The growth spurt accompanying puberty typically begins even before the breasts start to develop. Growth is fastest relatively early in puberty (before menstrual periods begin) and peaks at about age 12. Then growth slows considerably, usually stopping between the ages of 14 and 16.