Women are born with their lifetime supply of eggs, and these gradually decrease in both quality and quantity with age.​ AMH is a hormone secreted by cells in developing egg sacs (follicles). The level of AMH in a woman's blood is generally a good indicator of her ovarian reserve.  AMH does not change during your menstrual cycle, so the blood sample can be taken at any time of the month - even while you are using oral contraception.