Eggs are saved during the ovaries and they are only released with the right hormonal stimulation. So, the doctor collects a blood sample and checks it for three critical hormones: follicle-stimulating hormone (FSH), which triggers the growth of ovarian follicles prior to ovulation; estradiol, that's made primarily through the ovaries https://zed-directory.com/listings13016889/new-step-by-step-map-for-egg-freezing