Menopause
The menopause transition typically begins between 40 and 50 years of age (average 47.5). The duration of perimenopause may be for up to eight years. Women will often, but not always, start these transitions (perimenopause and menopause) about the same time as their mother did.
Folliculogenesis
The supply of follicles decreases slightly before birth, and to 180,000 by puberty for the average case (populations at puberty range from 25,000 to 1.5 million). By virtue of the "inefficient" nature of folliculogenesis (discussed later), only 400 of these follicles will ever reach the preovulatory stage. At menopause, only 1,000 follicles remain. It seems likely that early menopause occurs for women with low populations at birth, and late menopause occurs for women with high populations at birth, but there is as yet no clinical evidence for this.