Menopause is actually a moment/day in time. For women with a uterus, menopause occurs when they have gone one year without a menstrual period. For those of us without a uterus, menopause occurs when the FSH (follicle stimulating hormone) is above a certain number and the estradiol level is below a certain number. The numbers are different for each lab, Lab Corp defines post menopausal as an FSH above 25.8, and as of October 2010, mine was 34.0. Estradiol levels are postmenopausal when they are less than 54, mine is 40.
While I obviously do not agree with the suggestions about hormonal therapy and/or antidepressants discussed in this article from AOL.com, there is some good information about the perimenopausal transition. The article is worth a read.