Freezing embryos is an effective procedure that allows them to be stored for months or years.
At present, vitrification is used, a method of rapid freezing with very high survival rates on thawing.
Frozen embryos are stored in small devices called sequins, stored in liquid nitrogen, at temperatures of -1960 C. The embryo bank is constantly monitored and fed with liquid nitrogen, to ensure optimal storage conditions.
What embryos freeze?
Only embryos considered viable, according to international scientific criteria
- Additional viable embryos remaining after embryo transfer
- Sometimes all viable embryos obtained, if there are low risks or chances at that time
Chances of success and risks
- At least 90% of frozen embryos resist freezing and resume evolution after thawing.
- The chances of success are at least similar to the IVF procedure with non-frozen embryos
- The risks of pregnancy complications are similar to natural pregnancies
- From existing data, cryopreservation does not appear to increase the risk of fetal abnormalities.
How is frozen embryo transfer (TEC) performed?
- In the natural cycle (without treatment) or with hormonal support treatment
- Requires ultrasound and sometimes hormonal monitoring
- The establishment of the TEC moment is in the period of natural implantation or mimicked treatment
- TEC is done on the same day as thawing or after a period of embryo culture
How are embryos frozen?
Before freezing an embryo, it is dehydrated, so as not to form ice during freezing. As the water is removed, it is replaced with a cryoprotective medium; subsequently, the embryo is placed in a small container called a sequin and cooled rapidly (a process called vitrification). Frozen embryos are stored at -1960 Celsius in liquid nitrogen.
How are embryos thawed?
- The thawing of embryos is done in reverse to the freezing procedure. Embryos removed from liquid nitrogen, from -1960 C, are heated. The protective medium is progressively removed and replaced with water, until complete rehydration. Subsequently, the embryos are evaluated and incubated under special conditions.
How long can embryos be frozen?
- There is no known maximum period in which frozen embryos can be stored. Human embryos have been successfully frozen until 12–15 years of age. It is generally recommended to limit the storage period and the use of embryos after a maximum of 5 years.
Can freezing affect embryos?
- Some embryos may not tolerate the freezing and thawing process. If after thawing most of the cells recover, the embryo can resume its evolution. The survival rate depends on the stage and quality of the embryos, the cryopreservation method, but last but not least the experience of specialists. In the Gynera Clinic, over 95% of blastocysts recover evolution after cryopreservation by vitrification. Implantation rates of frozen blastocysts are also exceptional; over 50% of them are implanted and cause clinical tasks.