Cryopreservation is a process of preserving living cells using low temperature in such a way that they remain fully viable after thawing. Owing to cryopreservation techniques, frozen tissues and cells as well as embryos can be safely stored (banked) indefinitely in liquid nitrogen at -196°C.
The technique of cryopreservation has developed mainly to meet the need to preserve embryos that have not been implanted. Currently, semen or oocytes can also be successfully frozen. Effective cryopreservation of gametes is, in turn, important for preserving fertility, increases the efficacy of IVF and improves the comfort of patients undergoing assisted reproduction treatment.
Cryopreservation and freezing have made infertility treatment more flexible. The possibility of freezing the embryos enables the use of a larger number of oocytes for IVF, which increases the chances of success, and thus avoids patient exposure to further stimulations and oocyte collections. Embryos that have not been transferred into the uterus can be safely frozen for future cryotransfer. Additionally, embryo freezing allows for postponing the transfer until optimal conditions arise, when the level of hormones and the preparation of the endometrium will be optimal for embryo implantation.
Cryopreservation of embryos is a technique that has been commonly and routinely used for many years. Thousands of babies are born every year owing to cryopreservation. Although it may happen that a weaker embryo does not survive freezing, this technique is widely considered safe for embryos and is highly effective.
Freezing human sperm is a well-developed procedure that has resulted in the birth of thousands of babies. Freezing sperm is relatively simple and quick.
Planned anticancer therapy is a particular indication for semen cryopreservation. Cancer patients, especially those diagnosed with testicular malignancy, should be informed by their doctor about sperm freezing option. Sperm banking may be offered to a patient who is about to undergo chemotherapy or any other procedure that may compromise testicular function and sperm production.
Freezing your partner’s sperm also allows for an IVF procedure when a sample cannot be collected on demand or if the quality of the sample is poor on the day eggs are available. Sperm freezing is therefore a solution for patients who have undergone testicular or epididymal biopsy to collect generative cells. In such situations, a biopsy is taken before stimulation and then assessed for the presence of sperm. If the collected specimen contains sperm, it is frozen in order to be used for the planned IVF procedure.
Sperm freezing is routinely used for non-partner donations, where sperm from an anonymous donor are cryopreserved. Frozen donor sperm can be used for both IUI and IVF.
For donor insemination, samples are quarantined for 6 months prior to use, thus minimising the risk of transmitting infectious diseases. In other words, the donor is screened for sexually transmitted diseases at the time of collection, and the frozen sample is released for use 6 months later, when the donor has passed re-screening.
The use of frozen semen for insemination is limited, because sperm in semen with poor parameters usually do not tolerate freezing well, and therefore the quality of the sample may deteriorate. For this reason, the use of frozen semen for insemination in the case of oligozoospermia or asthenozoospermia is of little effectiveness.
An alternative solution may be to collect several frozen ejaculates and perform insemination with bulk samples. However, lower quality semen can be used in other ARTs.
Cryopreservation of very poor-quality semen, or even single sperm or testicular tissue may be considered for IVF using intracytoplasmic sperm injection. Insemination using frozen specimens can be successfully performed in patients with normal semen parameters. Therapeutic efficacy is then comparable to treatments using non-frozen material.
Sperm viability after thawing very much depends on semen quality. Weaker sperm may not survive the freezing procedure even despite the best possible management. Therefore, fresh semen is preferable if possible. While the freezing procedure itself may affect the amount of viable sperm in the sample, the storage of the frozen material itself can be continued indefinitely, as the storage time does not significantly affect the quality of sperm. Pregnancies have been achieved after using sperm stored at low temperatures for more than 10 years.
Cryopreservation of human oocytes is a procedure offered to patients who wish to preserve their fertility in the event of cancer, ovarian failure or other conditions compromising oocyte production.
It should also be noted at this point that oocyte freezing circumvents the ethical issues associated with embryo freezing and, in the event of failure of the first IVF cycle, it allows the patient to avoid subsequent stimulation and egg collection. Currently, the law in Poland limits the number of eggs that can be fertilised. If a surplus of normal oocytes is obtained during puncture, the patient may decide to freeze them for the next IVF.
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