Women are born with 1 Million to 2 Million (potential) eggs (or ovarian follicles). By the time puberty hits, there are about 300,000 eggs left. When we are young, our ovaries are full of follicles, and during ovulation, one usually dominates and is released. The others are absorbed (or are essentially lost). Each month when a woman cycles, she loses about 1000 eggs through the process. As we age, this number goes up.
So our ovarian reserve is kind of like a bank, but one that does not take deposits. There are three ways that doctors can assess our ovarian reserve in clinic, and now we have a test that will enable us to check it at home!