Interactions between serum FSH, inhibin B and antral follicle count in the decline of serum AMH during the menstrual cycle in late reproductive age.

Objective: To investigate the hormonal interrelationships during the menstrual cycle in women of late reproductive age with suppressed serum AMH and antral follicle count (AFC).

Methods: Serum hormones (AMH, FSH, LH, estradiol, progesterone, inhibin A, inhibin B), AFC (2-10 mm) and AMH/AFC ratio (an estimate of AMH/follicle) were assessed every 2-3 days across the menstrual cycle in 26 healthy ovulatory women aged 18-50 years.

Results: An 11-fold fall in AMH/AFC was observed in women aged ≥45 years compared to those 18-45 years ( < .001). Although women ≥45 years exhibited normal menstrual cycle patterns of serum estradiol, progesterone, LH and inhibin A, FSH was elevated ( < .001) and inhibin B suppressed ( < .001) compared to the younger group. Overall FSH was inversely correlated ( = .55,  < .05) and AMH directly correlated ( = .88,  < .01) with AFC; however, these relationships were curvilinear and more pronounced when AFC was low. Inhibin B was directly linearly correlated ( = .70,  < .01) with AFC across both high and low AMH/follicle groups.

Conclusions: It is hypothesized that the marked fall in AMH/follicle in late reproductive age is attributed to the change in the hormonal interplay between the pituitary and ovary. The fall in AFC leads to a decrease in inhibin B and a concomitant increase in FSH by a recognized feedback mechanism. It is postulated the elevated FSH suppresses AMH either directly or indirectly through oocyte-specific growth factors leading to a marked fall in AMH/follicle. We propose that pituitary-ovarian and intra-ovarian regulatory systems underpin the accelerated fall in AMH/follicle during the transition to menopause.