Legislation in Greece, allows cryopreservation of surplus embryos, following IVF treatment. Vitrification techniques are being used, which allow “frozen” embryo pregnancy rates to be almost the same as those of our fresh embryo transfers. Embryos can be frozen at different developmental stages – up to and including blastocyst stage. However, in some cases, freezing at earlier stages of development, may be beneficial for the embryos, as they are less susceptible to damage during the thawing procedure. Embryos are safely stored in straws immersed in liquid nitrogen, at –196 C.
During embryo thawing, the frozen embryos are warmed in a controlled manner, the day before the embryo transfer. This allows monitoring of embryos’ development, because some embryos may not survive the thawing process. On the day of transfer, the selected embryos are introduced, through a fine catheter, into the woman’s uterus, under ultrasound guidance, usually without causing discomfort.