At what stage are embryos frozen?
Embryos may be frozen at any stage of development between 1 and 6 days.
How long does it take for embryos to thaw?
Embryos thaw to room temperature within less than a minute or two after being removed from cryostorage, but the entire thaw process takes about 40 minutes before the embryo is ready for transfer or further incubation.
How does the thawing process work?
The embryos are removed from their canister and brought to room temperature. In a reversal of the preparation process for freezing, the cryoprotectant is gradually removed and replaced with water by incubating the embryos in increasingly dilute solutions, each containing more water and less cryoprotectant. Again, the embryo may burst when water rushes into the cells, so this process is carefully controlled. Then the embryo is brought to body temperature and transferred or is placed into culture medium in an incubator until transfer. Embryos are normally reevaluated before transfer.
Embryos thaw to room temperature within less than a minute or two after being removed from cryostorage, but the entire thaw process takes about 40 minutes before the embryo is ready for transfer or further incubation.
How does the thawing process work?
The embryos are removed from their canister and brought to room temperature. In a reversal of the preparation process for freezing, the cryoprotectant is gradually removed and replaced with water by incubating the embryos in increasingly dilute solutions, each containing more water and less cryoprotectant. Again, the embryo may burst when water rushes into the cells, so this process is carefully controlled. Then the embryo is brought to body temperature and transferred or is placed into culture medium in an incubator until transfer. Embryos are normally reevaluated before transfer.
How long can embryos be frozen and still be viable?
Theoretically, embryos may be frozen indefinitely, as no biological activity takes place during cryopreservation. In practice, it is unknown how long they can remain viable. The first frozen embryo transfers resulting in live birth took place in the mid-eighties. Since then, embryos frozen as long as 12 years have resulted in successful pregnancy. Freezing and thawing protocols continue to improve, making it possible that embryos frozen more recently may have better outcomes.
Theoretically, embryos may be frozen indefinitely, as no biological activity takes place during cryopreservation. In practice, it is unknown how long they can remain viable. The first frozen embryo transfers resulting in live birth took place in the mid-eighties. Since then, embryos frozen as long as 12 years have resulted in successful pregnancy. Freezing and thawing protocols continue to improve, making it possible that embryos frozen more recently may have better outcomes.
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