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.