During this event, Sofia Rodrigues, BSc, Clinical Embryologist at Ferticentro, Portugal explained the main differences and advantages as well as disadvantages of embryo banking vs egg freezing.
Egg freezing and embryo freezing are two valid forms of fertility preservation. Both have the same steps involved at the beginning of the process, which involves stimulation of the ovaries so that the follicles can grow and egg retrieval. If a patient wants to cryopreserve her eggs, those are selected by the embryologist after the egg retrieval, and they will be immediately cryopreserved. If a patient wants to cryopreserve embryos, those eggs will be fertilized with chosen sperm, and they will be left in the laboratory in culture for 5 to 7 days until the embryo reaches the blastocyst stage, which is the ideal structure of an embryo to be cryopreserved. However, if a patient cryopreserves her eggs, she can come to the clinic when she wants to use those eggs, and then the eggs will be thawed fertilized, and the embryos will be created and then transferred.
The survival rate after thawing
There is always the chance of loss during the thawing process for both embryos and eggs. The egg survival rate is between 80 to 90%, while the embryo survival rate is higher than 95%. The survival rate of eggs is a bit lower than that of embryos because the eggs are single cells, and a single cell is much more fragile and much more sensitive to the process of freezing and thawing, it is more likely to be damaged in that process. The success of the thawing of eggs is also related to the egg quality itself, which is tightly linked with the age of the woman that wants to collect her eggs. It’s important to remember that the quality of the egg decreases with the increasing age of the woman. A younger woman has a higher chance of survival rate of the eggs.
On the other hand, when an embryo doesn’t survive the thawing, it is because the embryo is composed of a hundred cells and it gives them a stronger structure, which is more resistant to the cryopreservation and thawing processes. However, these survival rates alone should not be the main determinant to choose between cryopreserving eggs or embryos.
Egg freezing – advantages & disadvantages
One of the biggest advantages of egg freezing is that it doesn’t require sperm, so eggs are frozen and can be stored for a later date and used later in life. This is an optimal choice for single women who haven’t found a partner yet or haven’t decided if they want to use a sperm donor, and it also gives reproductive autonomy to the woman because she can preserve her own fertility independently whether she has a partner or not. This gives higher flexibility to make different choices. Freezing eggs brings fewer ethical considerations compared to freezing embryos because an embryo is a certain form of life, an embryo will implant and generate a living being, and it’s easier to discard oocytes rather than embryos if that’s the case.
The disadvantage of freezing eggs is a lower survival rate after thawing, it has a lower survival rate compared to embryos, and it’s hard to say how many eggs will survive the thawing. After they survive, it’s also hard to say how many will fertilize and develop into blastocysts. Therefore, more eggs are needed to improve the chances of pregnancy. It’s also important to remember that the egg doesn’t give a lot of information about its quality or genetics because it’s not possible to test it.
Embryo freezing
One of the advantages is that it has a higher survival rate after the thawing. It’s possible to monitor and see the development of a fertilized egg until the blastocyst stage, which gives a lot more information about the embryo. When the embryo reaches the blastocyst stage, it allows to do a biopsy, it’s possible to remove some cells of the blastocyst for them to be genetically tested. Thanks to this procedure, it’s possible to know if it is genetically normal and whether it can give a viable pregnancy or not. These advantages give a higher success rate when it comes to embryo freezing rather than egg freezing.
The disadvantages include the necessary use of sperm. Therefore, if a woman chooses a different partner later in life, she may not be able to use previously cryopreserved embryos because if both gamete providers split up, the woman cannot transfer those embryos without the consent of the other partner who created the embryo. This can raise some legal issues when it comes to transferring such embryos.
The choice between freezing eggs versus embryos depends on your current social situation and your goals. Although freezing embryos have higher success rates, freezing eggs gives more flexibility and more choices in the future. If you are a single woman and want to preserve your fertility, then egg freezing may be the best option for you, but if you and your partner plan to have children in the future but want to delay the pregnancy, then embryo preservation will be an option to consider. However, it is important to remember that couples don’t always stay together, and if you change your partner, you may not be able to use the embryos that you created before.
