Basal and stimulated gonadotropin levels in the perimenopause

We investigated whether perimenopausal menstrual cycle irregularity is associated with increased gonadotropin immunoactivity, bioactivity, or the bioactivity/immunoactivity ratio at baseline and after short-term stimulation with gonadotropin-releasing hormone.

Subjects consisted of four groups: (1) young regular cycling women (< 35 years old), older women (> 35 years) with (2) regular or (3) irregular menstrual cycles, and (4) postmenopausal women. Gonadotropin-releasing hormone stimulation tests (100 micrograms intravenous gonadotropin-releasing hormone) were performed in the National Institute of Mental Health outpatient clinic during the follicular phase of the menstrual cycle or randomly in postmenopausal women.

Perimenopausal women had baseline follicle-stimulating hormone and luteinizing hormone levels and stimulated follicle-stimulating hormone levels (area under the curve) that were similar to those of postmenopausal women and significantly greater than those of control (younger and older) women. Postmenopausal women had significantly greater baseline levels of luteinizing hormone bioactivity than did the other three groups. The bioactivity/immunoactivity ratio in the postmenopausal women was significantly greater than those in the perimenopausal and older cycling women, which were similar. No change in the bioactivity/immunoactivity ratio was seen after gonadotropin-releasing hormone stimulation in any group.

Although the perimenopause is associated with increases in baseline and stimulated gonadotropin levels similar to those seen after the menopause, significantly increased baseline luteinizing hormone bioactivity and the bioactivity/immunoactivity ratio are seen only after the menopause.