Cryopreservation – freezing of embryos (vitrification)
The purpose of ovarian stimulation in IVF is to produce several eggs and therefore embryos in order to be able to select the best ones for embryo transfer. Embryos that will not be selected for transfer to the uterus may be frozen under controlled conditions and stored in liquid nitrogen at -196oC, a temperature that inhibits their further growth.
Freezing the embryos can be done either on the next day of egg retrieval when they are at the two pronuclear stage (2PN), or on the second or third day following egg-retrieval or the fifth day after the egg-retrieval, and are therefore at the blastocyst stage.
The decision for cryopreservation of embryos belongs exclusively to the couple, because they have to consider moral, philosophical or religious issues. However, the official position of the Church of Greece does not condemn cryopreservation. The Greek law allows for embryo cryopreservation.
On the day of embryo transfer we will provide you with a written analysis of our embryologists that will include the number and quality of embryos that are suitable for embryo transfer or freezing and we will help you make the right decision. Dr. Ioannidis’ recommendation is to freeze only embryos that are of good quality, for the simple reason that them only have an adequate thaw survival rate (80% internationally) and they stand a serious chance of achieving pregnancy. In either case, the couple will discuss with the physician about ‘if’ and ‘when’ cryopreservation will be performed and the decision is taken jointly.
The purpose of the remaining embryos cryopreservation is, in the event that the “fresh”IVF cycle fails, that the woman will undergo another embryo transfer and will achieve possible pregnancy, without being subjected to the ovarian stimulation and egg retrieval process again. The success rate of this process is slightly lower than the one corresponding to the “fresh” cycle.
Human embryos have a high water content and are therefore very sensitive to freezing processes. In any case, the freezing process is the same and involves placing the embryos in special biological cryoprotectant fluids and storing them in liquid nitrogen in very thin recipients, which are individual and bear the couple’s names.
There are two cryopreservation techniques, slow programmable freezing and fast vitrification techniques. In slow programmable freezing, the egg / embryo freezing rate is about 0.3 ° C per minute, and with the vitrification method this rate exceeds 20,000 ° C per minute. Although vitrification is not a new technique, after 2010 it has gained universal acceptance due to its advantages. Vitrification prevents the damage caused by the formation of crystals inside the cells and significantly increases the thaw survival rate of the embryos. It is also possible to observe each stage of the process in the laboratory, having full control over it.
The safety of cryopreservation methods has now been fully documented in the international literature. Studies show that children born after cryopreservation are perfectly healthy, even if the embryos have remained in the frozen for many years (up to 5).