During ovarian tissue Cryopreservation, small pieces of ovarian tissue-
or, in some cases, the entire ovary- are frozen and then re-implanted.
As Prof. Donnez puts it,"[T]he same applies for Cryopreservation of ovarian tissue, before the age of 25 ideally, because
we know that the number of follicles and number of eggs is highest in really young women.".
In practice for many years, oocyte Cryopreservation(a. k. a. egg freezing)
is an option for women who want to preserve their fertility in light of illness, such as cancer when chemotherapy may harm function of the ovaries.