How Embryos are Frozen and Thawed

Frozen embryo cryostorage

There are more than 600,000 frozen embryos in storage in the United States and the number is growing every day. Some of those embryos will be taken out of frozen storage and thawed to be used by either the genetic parents or by adoptive families through embryo adoption. But how does the freezing and thawing process work? And how successful is it?

Embryos not being used in an in vitro fertilization process are frozen in a solution known as cryoprotectant. This solutions prevents the growth of ice crystals within the cells of the embryo, which can damage the delicate tissues. The cryoprotectant actually replaces the water that’s in the cells, dehydrating them without destroying them. The embryos are then cooled down to -30° C and stored in liquid nitrogen.

The thawing process essentially works in reverse. The cryoprotectant is removed from the embryo and replaced with water, rehydrating the cells. The embryo is warmed up much faster than it is cooled, using air and warm water baths, in as little as 20 minutes. Rapidly thawing the embryo prevents any ice crystals from forming and damaging the cells.

How successful are these methods? The success rates depend on the clinic performing the procedure as well as the general health of the embryos before they went through the process. However, while not all embryos will survive being frozen and thawed, the majority of them will and can be used for frozen embryo transfer and given a chance to experience the life they were created to have.

Want to learn more about the embryo freezing and thawing process? Visit EmbryoAdoption.org.