When is it safe to switch from oral contraceptives to hormonal replacement therapy?

Women may continue to use oral contraceptives (OCs) into their 40's and 50's, but to date no method has been evaluated to ascertain their ovarian status, i.e., whether fertility and estrogen production have diminished sufficiently so they could be safely switched to hormonal replacement therapy. A group of 12 postmenopausal women who had been, for long periods of time, on a regimen of 3 back-to-back packages (i.e., 63 days on, 7 days off) of low-dose oral contraceptives have been studied. Secondly, a group of 9 perimenopausal women aged 36 to 47 were examined in the same manner. The third group consisted of early reproductive age women (arbitrarily divided into subsets aged 17-25 and 26-35 using low-dose OCs in the customary regimen) as normal controls. Blood samples were obtained on the last day of a pill cycle and at 7 days off the pill. In some menopausal women, blood samples were obtained at both 7 and 14 days off OCs. Serum was assayed by RIA for estradiol, FSH and LH. As expected in the young reproductive age women, estradiol levels increase at one week off the pill, together with a rebound in FSH and LH to follicular phase levels. In the perimenopausal group, there was a sharp distinction based on age. The women over 40 showed a more marked rise in FSH while those aged 36-40 showed a distinctly lesser response. Estradiol levels were variable, but tended to show some age grouping. Little diagnostic separation was observed for LH. In postmenopausal women, FSH levels were not always elevated at one week post-pill, and even in a second trial with sampling at one and two weeks off the OC, not all postmenopausal women showed a "menopausal" increase in FSH. The more uniform feature was that estradiol levels never increased above basal values. The study found that serum estradiol levels increase after a week off the pill in controls, but are unchanged at one and two weeks in the menopausal group. FSH levels rebound normally in reproductive age women and usually, but not always, increase substantially in postmenopausal women. After two weeks off OCs, an increased FSH and/or no change in basal estradiol levels is strong evidence that it is now safe (contraceptively speaking) to switch from OCs to standard hormone replacement regimens.