dr. mitchell rosen, director of ucsf fertility preservation center. we heard about environmental causes of infertility. is that difficult to diagnosis? >> it's very difficult to diagnosis because we don't how to get at the etiology or how to determine if that veont for not getting pregnant. when we evaluate them nd of do our usual evaluation but we don't know the reason for those environmental exposures. >> and fertility preservation center, what does the name mean? >> it's basically a program that is designed to give treatment that will eggs, sperm, freezing tissue all to try to help retain fertility potential. so, for example, if a patient were to be exposed chemotherapy because they were undergoing treatment for cancer which is basically their life saving treatment, that treatment can cause significant reproductive impairment. so we can do the so they don't deal with a double blow. >> eric: how long can you keep eggs and sperm viable? >> i call for an indefinite period of time. >> forever? >> forever, yeah. few companies may. there is a report that