In girls, there is a fall in estradiol levels in the first week of life, and then a gradual minimal rise that continues for one to two years. In boys, testosterone levels rapidly decrease in the first week of life, and then increase to pubertal levels for two to four months before declining. The period between infancy and puberty are marked by very low levels of gonadotropins and gonadal steroids. Normal Puberty Human puberty is defined as the transition between the juvenile state and the mature reproductive state when secondary sex characteristics develop and fertility is achieved. It is composed of the relatively synchronous processes of adrenarche and gonadarche.
Adrenarche occurs usually one to two years before gonadarche and is independent of gonadarche.
Children without functioning gonads will achieve adrenarche. Puberty includes the adolescent growth spurt, growth of pubic and axillary hair in males and females, and specific secondary sex characteristics for males and females. The age of puberty has been decreasing over the past several hundred years of written documentation in Europe and the United States. Although the age of male puberty is not as well documented as females, suggestions from northern European village records suggest that the age of menarche may have declined from as late as 18 to the current 12.8 years. The earliest manifestation of puberty in females is adrenarche.