Althought this cycle occurs in roughly monthly cycles, the actual number of days in any individual woman's cycle can be anywhere between 20 and 40 days.
Menstruation begins in puberty and ends with menopause .
The cycle ends just before the next menstrual period. Menstrual cycles range from about 21 to 40 days. The intervals between periods are generally longest in the years immediately after menarche and before menopause. FSH stimulates the growth of numerous follicles in the ovary as well as the release of oestrogen from the ovary. The oestrogen causes thickening of the endometrium.