Embryo Freezing

It has been almost 30 years since the birth of the first child conceived from a frozen human embryo. Nowadays, the technique of embryo cryopreservation is widely accepted and used.


During the IVF procedure, usually more than one embryo is created in order to have the option to select excellent quality embryos for transfer. This creates the need to cryopreserve the supernumerary embryos that present normal development and morphology. Cryopreserved embryos are stored in the laboratory under excellent conditions, in special canisters with liquid nitrogen, and may be thawed for embryo transfer at any point in time in the future. The method of embryo cryopreservation has proven to be life-saving in the case of OHSS (ovarian hyperstimulation syndrome), when embryo transfer is counter-indicated. Furthermore, the so-called freeze all strategy (cryopreserving all the embryos created in one IVF cycle) provides the option to perform embryo transfer in a subsequent cycle, when the woman will not have been submitted to ovarian stimulation. In this way, any potentially adverse effect on the receptivity of the uterus from the hormones used to induce ovulation is eliminated.

Our laboratory employs the new method of vitrification for embryo cryopreservation; vitrification has contributed to improved outcomes, by protecting embryos from ice crystals forming during freezing. The survival rate for cryopreserved embryos at our unit is almost 100%, and pregnancy rates are almost equal to those with non-frozen embryos.

Frozen embryos are stored for a period of 5 years; at the end of this time, the couple has the option to renew storage for another 5 years. When the above deadlines have elapsed, the embryos are either made available for research purposes or destroyed, with the couple’s consent.