Women experience two lifetime reproductive transitions (puberty and
perimenopause). The purposes of this chapter are to propose an update in terminology for
the transition to menopause, to describe the hormonal changes during this important life
phase and to show that perimenopause is a time of major bone loss. This new terminology
means that any woman over the age of 35 (and sometimes younger) who, despite regular
flow, experiences typical midlife changes (such as night sweats, heavy flow, increased
cramps) is considered to have entered early perimenopause. Late perimenopause is the 12
months after the last menstruation. Menopause (sometimes called “postmenopause”) then
commences and continues for the remainder of women’s lives. Hormonal changes in
perimenopause are extremely complex and reflect dys-regulation and eventual cessation of
the highly coordinated interplay of ovarian, pituitary and hypothalamic hormones within
the menstrual cycle. Among other changes, perimenopausal estradiol levels are variable
and often higher, ovulation becomes disturbed and luteal phase progesterone levels become
lower. A second, higher estradiol peak (luteal-out-of-phase event, LOOP) may also occur.
Bone changes are primarily related to variable estradiol, insufficient progesterone and
perhaps to increasing gonadotropin levels. Usual weight gain decreases midlife bone loss.
Increased cancellous bone loss in the spine (by quantitative computed tomography) and
total hip (dual energy X ray absorptiometry) are primarily related to higher bone resorption,
and become maximal in the late menopausal transition and late perimenopause. In
summary, the perimenopause involves major changes in experiences, menstrual cycles,
hormone levels and bone physiology.
Keywords: Perimenopause, early menopause transition, late menopause transition,
vasomotor symptoms, night sweats, hot flushes, estradiol, progesterone, anovulation, short luteal phase cycles, inhibin, anti-mullerian hormone, follicle
stimulating hormone, ovulation disturbances, bone loss, osteoporosis risk.
