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Cryopreservation of Ovarian Tissue

Ovarian tissue freezing is a process in which very small pieces of the ovary are frozen and preserved in liquid nitrogen. Ovarian tissue freezing is an experimental procedure that may enable patients to preserve fertility prior to chemotherapy, radiotherapy, or prior to removal of their ovaries by surgery.

Only small pieces of ovary may be preserved in this way, but if the patient is young, those small pieces may contain thousands of eggs. The process of freezing such small pieces of tissue is relatively well established. However, the process of utilizing these small pieces of tissue to achieve pregnancy in humans has not yet been worked out. Pregnancies have been achieved in sheep, but those techniques may not be suitable for humans. The best that can be said at this time, is that there is a great deal of optimism among reproductive biologists that the details of how to use this tissue to achieve pregnancy in humans will eventually be worked out.

The process involves taking small biopsies or pieces of the ovary. The size of these pieces is about the size of a grain of rice. The biopsies are placed in cryoprotective media (special fluid) and frozen with a controlled rate freezer in liquid nitrogen. The biopsies are then stored in liquid nitrogen at a temperature of -190C. This temperature is below the minimum temperature required for chemical reactions to take place, and theoretically there is no limit on how long the tissue can be stored.

Alternatives to this procedure which preserve fertility, are to undergo an IVF cycle in which as many eggs as possible are obtained. The eggs need to be fertilized and then frozen as embryos. Technology to freeze unfertilized eggs and achieve pregnancy is still viewed as experimental (although the technology for this seems to be reasonably worked out at this time).

Ovarian freezing is clearly still experimental.