What can be stored?
Cryopreservation is also a common method used in fertility treatment. In Germany (country-specific), several different materials can be frozen:
• Unfertilised eggs
With unfertilised eggs, there is still a relatively high risk that they can be damaged during the cryopreservation process. The reason for this is that the unfertilised eggs have a much greater sensitivity to the freezing process due to their higher water content (compared to fertilised eggs). Water crystals that form during the freezing process can therefore cause more damage. Nevertheless, the frozen, unfertilised eggs are still a valuable egg store which can be used to conceive children in the future.
• Fertilised eggs in the pronuclear stage
By using special cryopreservation procedures in which cells are mixed with a membrane-protecting medium, the cryoprotectant, and computer-assisted temperature programs that control the freezing process, the cells are put in a state that ensures that they can be stored over long periods (years) without impairing their viability and then thawed as required.
In Germany, under the Embryo Protection Law, embryos may be frozen only in exceptional cases.
As part of infertility treatment, cyropreservation of sperm may be necessary due to the prolonged absence of the partner, a health condition, or difficulty on the part of the man to provide sperm on demand (psychological impotence).
• Testicular tissue
Testicular tissue obtained in a biopsy (see TESE), can be frozen for later sperm retrieval. The availability of this previously surgically removed tissue allows for hormonal stimulation of the ovaries in the woman without time restraints. In addition, multiple biopsy samples can be individually frozen for several ICSI attempts.
• Ovarian tissue
Thanks to state-of-the-art cryopreparation techniques, it is possible to carefully freeze tissue without impairing the physiology of the cells. In order to fulfil a desire to have a child, the thawed, intact ovarian tissue can be re-implanted after several years of cryopreservation (autotransplantation). It is also possible to remove the eggs that have matured in the ovarian tissue from the cryopreserved tissue at a later date and use these for artificial insemination.