Gonadotrophin excretion in fertile women: effect of age and the onset of the menopausal transition.

In normal women the menopausal transition starts typically with a sudden break in regular menstrual cyclicity: gonadotrophin levels escape from the cyclical pattern characteristic of fertile women and increasingly rise into the postmenopausal range. An investigation was undertaken to determine whether this rise precedes the first appearance of ovarian dysfunction. Weekly urine samples for the measurement of FSH, LH and pregnanediol were collected from 100 women, all of whom had regular 20- to 35-day menstrual cycles (504 samples from 48 women aged 20-39 years and 620 samples from 52 women aged 40-48 years; 96.8% of these cycles were shown to be ovulatory). Excretion rates of FSH in excess of 5 i.u./24 h occurred more often in women aged greater than or equal to 40 years than in younger women (incidence, 31.5 cf. 19.5%; P less than 0.001). The difference was greatest at the time of the perimenstruum (7-day incidence, 32.5 cf. 13.9%) and declined to insignificance during the mid-cycle gonadotrophin surge (7-day incidence, 44.2 cf. 34.8%). Examination of the rank correlation between age and gonadotrophin excretion confirmed the age-related rise in FSH and identified a lesser but significant perimenstrual rise in LH. For both FSH and LH these changes were small compared with the increases observed in nine women presumed to have reached the menopausal transition during the trial (incidence FSH greater than or equal to 5 i.u./24 h, 60.6%; incidence LH greater than or equal to 5 i.u./24 h, 48.6%). It is concluded that in fertile women there is evidence of an age-related rise in FSH which is distinct from the changes occurring at the start of the menopausal transition.