The current freezing methods allow to obtain a significant percentage of embryos which are properly thawed after freezing. However, there is no absolute certainty that the embryos will thaw out properly, and that after thawing they will be capable of further appropriate division and then implantation in the uterus.
Theoretically, cryopreservation techniques may damage embryos. At present, no data, either those obtained during many years of observational studies in animals or those relating to cryopreservation in humans, provide evidence that more anomalies are observed in children born in the result of freezing and then thawing and transfer of thawed embryos than in children born in the result of the so-called fresh IVF cycles.
The freezing of normally developing embryos is performed in every case of the so-called supernumerary embryos remaining after the embryo transfer. It is considered that a normally developing embryo is the embryo with cell divisions occurring in accordance with the accepted morphological classification corresponding to a given culture day, and in case the PGD diagnosis is performed, the embryo which also has the normal result of the performed genetic test.
Embryos are usually frozen on day 1 or 5/6 of the culture. Confirmation of the embryo freezing process includes a statement that a deposit has been made and with information on the quality and number of frozen embryos.
It is not possible to destroy normal embryos. It is possible to withdraw from the embryo freezing procedure during any cycle of IVF treatment, but in all cases it is associated with anonymous donation of embryos under normal development to the Bank of Embryos, for a further transfer to recipients and/or donating embryos for educational or research and development purposes.
An alternative to withdrawal from a decision to freeze supernumerary embryos is to fertilize a specific number of egg cells and to freeze the remaining egg cells.
With regard to a deposit of egg cells or embryos, it is possible to cancel further storage of a deposit, which is associated with transferring this deposit to the bank of anonymous donors of egg cells and embryos. Withdrawal from further storage has to be confirmed in writing by a person who makes a deposit of egg cells, and in the case when embryos are deposited – by both partners participating in a treatment cycle from which a given embryo originates.