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Embryo cryopreservation is the process of preserving fertilized eggs for possible implantation; this is done for a variety of reasons. The embryos are frozen and stored at extremely low temperatures until they are needed. While embryo cryopreservation can be a good safeguard for those looking to preserve their fertility options, the freezing and subsequent thawing of the fertilized eggs can significantly decrease their viability.
When a woman or couple undergo in vitro fertilization (IVF) treatments, there is often a surplus of eggs. Typically, each egg harvested is fertilized to create an embryo. This increases the likelihood of creating several healthy embryos viable for transplant. As only so many embryos can be implanted at once, this often means one or more fertilized eggs are left over; those remaining are then often preserved for later use.
In other cases, embryos are created with the sole purpose of freezing them. Those with health issues that may affect their fertility later in life may choose to do embryo cryopreservation to have the chance or option of having a biological child. While fresh embryos provide a better chance of carrying a child to term, frozen embryos can limit the amount of IVF cycles a woman has to undergo. Since these cycles are often painful and exhausting, embryo cryopreservation can be a good option.
One to five days after the eggs are fertilized with sperm, they can be tested for quality and then frozen. Healthy embryos are mixed with a cryoprotectant solution to prevent ice from developing, and then placed in airtight vials. The vials are then slowly cooled to -400° Fahrenheit (-196°Celsius); the freezing process takes several hours. Once the desired temperature is reached, the embryos are stored in liquid nitrogen, where they can remain frozen for up to 10 years.
Embryos are almost always frozen in batches. The patient and fertility specialist typically discuss how many embryos will be implanted in the future before they undergo embryo cryopreservation. This way, only the embryos to be implanted need to be thawed. Once the embryos are needed, they are thawed, which can take less than an hour. The embryos are cleaned to remove the cryoprotectant solution and then implanted.
Each stage of embryo cryopreservation can result in the destruction of the embryo. Even if the embryo is still viable after freezing and thawing, it is significantly less healthy than a fertilized egg that has not undergone embryo cryopreservation. Typically, only 32% of implantation procedures with a previously frozen embryo result in a live birth. While this number is relatively low, many women have been able to give birth to a biological child with the help of IVF and embryo cryopreservation.