Definition of Menopause versus Postmenopause
Menopause is defined as no menses for 12 months in the absence of chemotherapy or tamoxifen use, or immediately following surgical removal of all ovarian tissue, while postmenopause refers to the entire period after this 12-month threshold has been met. 1
Menopause Definition
The NCCN Guidelines provide specific criteria for determining menopausal status 1:
- Prior bilateral oophorectomy (immediate menopause regardless of age) 1
- Age ≥60 years (presumed menopausal) 1
- Age <60 years with amenorrhea ≥12 months in the absence of chemotherapy, tamoxifen, toremifene, or ovarian suppression, AND FSH and estradiol in postmenopausal range 1
- If taking tamoxifen or toremifene and age <60 years, FSH and plasma estradiol must both be in postmenopausal ranges 1
The median age of natural menopause is 51 years, with 95% of women reaching menopause between ages 45-55 years 1
Postmenopause Definition
Postmenopause encompasses all time after the 12-month amenorrhea threshold has been met. 1 This represents the permanent cessation of ovarian follicular activity and profound, permanent decrease in ovarian estrogen synthesis 1. Women in developed countries can expect to live approximately 30 years postmenopause, representing up to one-third of their lifespan 1, 2.
Critical Distinctions and Pitfalls
Chemotherapy-Induced Amenorrhea
Amenorrhea after chemotherapy is NOT a reliable indicator of true menopausal status because ovarian function may resume even after >12 months of amenorrhea 1. For women with therapy-induced amenorrhea:
- Require amenorrhea for at least 2 years (not just 12 months) 1
- Serial FSH and/or estradiol measurements are mandatory if considering aromatase inhibitor therapy 1, 3
- Both FSH and estradiol must be in postmenopausal range to confirm status 3
- Oophorectomy or persistent postmenopausal hormonal profile plus vaginal ultrasound showing non-functioning ovaries may be needed 1
Patients on LHRH Agonists/Antagonists
It is impossible to assign menopausal status to women receiving LHRH agonists or antagonists (GnRH agonists) 1, 3. Testing must be deferred until after discontinuation of these medications 3.
Aromatase Inhibitor Considerations
Aromatase inhibitors can paradoxically stimulate ovarian function 3. If vaginal bleeding occurs while on an AI, immediate physician contact is required 3. For women <60 years who are amenorrheic for ≤12 months prior to starting adjuvant endocrine therapy, monitor estradiol and FSH/LH levels 3.
Physiologic Basis
The transition reflects profound depletion of ovarian follicles, with menopause occurring when remaining follicle count reaches ≤1000 1, 4. This results in permanent loss of reproductive hormone production and irreversible infertility 5. The process involves declining inhibin B levels (reflecting follicle loss), rising FSH, and eventual estradiol decline in late perimenopause 4, 6.