Antimüllerian hormone (AMH) in women informs us of the number of ovarian follicles available, independent of the menstrual cycle and the age of the patient, although it is usually related to her reproductive age.
It is known that women are born with a finite follicular endowment that is depleted as they get older, therefore, a low antimüllerian is indicative that the number of total follicles available in the ovary is decreased. Fewer follicles available means less response. But this is not entirely true, since we have to take into account another important factor which is the AFR (Antral Follicle Count).
Each menstrual cycle the ovaries make a number of follicles available for development each cycle. This number of available follicles usually decreases with age but does not necessarily depend on the remaining count in the ovary. Let's say that they are complementary because what really defines the low response is the number of follicles available in each cycle (RFA) which is usually lower the AMH. They are usually related, but what really defines the low response is not AMH but the AFR.