Embryo Freezing (Vitrification)

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Embryo Freezing - Cryopreservation


Embryo freezing - vitrification

Embryo freezing is a process where one or more embryos are frozen to store them as a backup for future use. Embryo freezing is associated to In Vitro fertilization (IVF), a procedure where the eggs are aspirated from a woman’s ovary and combined with sperm in the laboratory to form embryos. The embryos are frozen and can later be thawed and placed in a woman’s uterus by a procedure called Frozen Embryo Transfer (FET). Embryo freezing is a type of fertility preservation. This is also called embryo banking and embryo cryopreservation. 

Most in vitro fertilization (IVF) programs use embryo cryopreservation to achieve pregnancies from a single ovarian stimulation. The more embryos are created, the more extra embryos are obtained for freezing, and the higher the pregnancy rate will be by increasing the cumulative pregnancy rate through frozen embryo transfer. The best protocol of embryo freezing involves growing embryos to a further stage of development, day 5 – 6 after fertilization, where we can choose only the embryos with proven developmental capabilities to be cryopreserved.  
Treatments such as IVF, ICSI and Egg donation often produce more embryos than required for the treatment. If those extra embryos are of a sufficient good quality at day 5 – 6, they can be frozen and placed in storage for your future use. Only the good quality embryos that have the potential to survive freezing and be viable once they are thawed are frozen. We place those embryos in storage to provide another possibility of pregnancy without having to repeat the process of ovarian stimulation.
Why is embryo freezing (cryopreservation) done?
There are many reasons why a couple might choose to freeze and store the embryos:
They may feel psychologically relieved by the idea that the extra embryos will be frozen to be used later instead of being destroyed.
Embryo freezing can provide another chance to get pregnant in case the IVF process fails. The couple will not have to go through injections and IVF again.
If the IVF succeeds and the couple gets a baby, they can use the frozen embryos later to have a second baby without passing through the process of ovarian stimulation and injections which will cost them less.
The couple can freeze embryos before he or she begins any treatments that can harm their fertility potential, such as cancer treatment that might reduce or eliminate their chances of having children. It’s a method to preserve fertility.
Cryopreservation of extra embryos is a helpful tool in increasing the pregnancy chances by increasing the cumulative pregnancy rate per oocyte retrieval.


Are you obliged to freeze the extra embryos?
No, it is not necessary to freeze the extra embryos, but the doctors recommend doing it because it finds a solution for the ethical problem of discarding the extra embryos and it provides the opportunity of a pregnancy in case the fresh embryo transfer doesn't work - without having to go through the whole treatment again.
Can all embryos be frozen and stored?
Unfortunately not all the embryos are suitable for freezing. The extra embryos will be cultured until 5 - 6 days after egg retrieval to see if they develop to the blastocyst stage. This enables us to select the best quality embryos, as blastocysts have a greater potential to develop and implant. Only the embryos that make good quality blastocysts will be frozen, as we know from experience that most of those embryos are capable of surviving the freeze/ thawing process.
How are the embryos frozen? 
The embryos can be frozen and stored at a low temperature for future use just as with sperm and eggs. In order to carry out this embryo storage, a procedure of embryonic freezing has to be done. The old way of embryo freezing didn’t have good successful rates of implantation. But now the best technique in the world is vitrification. The new, advanced method known as Embryonic Vitrification offers greater effectiveness in survival of the embryos after thawing as well as a better rate of implantation, clearly increasing pregnancy rates. Vitrification cools the cells in an extraordinarily fast way, unlike the classic slow freezing process. This way the liquid in the embryo will not have time to form crystals. Therefore there is no damage to the embryos caused by ice crystals which are formed during the slow freezing technique. In the past, the embryos were slowly cooled without being able to avoid the formation of ice from the water inside and surrounding the embryos. However, vitrification cools the cells immediately so that there is no time for ice to be formed, but instead a kind of gel appears leaving the cells undamaged. Thus, we can ensure better rates of implantation and embryo survival after thawing. Now by using vitrification, more than half of the frozen embryos can achieve pregnancy after thawing.
Does freezing the embryos have a harmful effect on them?
Studies show that there is no evidence that the freezing process is harmful to the ability of the embryo to develop into a normal baby. There is no increase in the risk of birth defects among children born from frozen embryos compared with normal births.
How long can embryos be stored? 
The frozen embryos can be stored as long as the couples want. There is no time limit for storing the frozen embryos as long as the couples extend the storage period by renewing the consent and by paying the yearly maintenance fees for the freezing. There is no known deterioration in the health of the frozen embryos with time. Research shows that the freezing and thawing of embryos does not harm subsequent babies made through IVF. The time duration the embryo was stored does not affect IVF success rates.
Will the embryos survive the thawing process? 
Approximately 95% of the embryos will survive the thawing process, but there is no way to predict their survival until they are thawed.
How long does it take to freeze (vitrify) and thaw the embryos? 
The Embryo freezing process by vitrification takes 6 – 15 minutes while the embryo thawing process takes about 15 minutes. After the thawing process of the embryos that were frozen at the blastocyst stage they need about 2 hours of rest in the culture media before the transfer to the uterus. Embryos frozen at the blastocyst stage are thawed in the same day of the frozen embryo transfer.
Sometimes after thawing the embryos that were frozen before day 5 – 6, we grow them for a day or more in the lab to see if they can develop further to reach the blastocyst stage before the embryo transfer is done. 
How many embryos we usually thaw? 
In most cases we thaw a single embryo initially and assess its viability. We thaw an additional embryo only if the first embryo does not survive the thaw or if the couple insists on transferring 2 embryos which will increase the risk of a multiple pregnancy. Some patients may be eligible to have a double thaw and transfer of 2 embryos. In all cases, the number of embryos to be thawed and transferred will be discussed with the couple.
Pregnancy success rate of embryo transfer (FET)? 
The frozen embryo transfer has the same pregnancy success rate as the fresh embryo transfer. 
The pregnancy success rate in fresh embryo transfer depends on the age of the woman.  In case of FET, the success rate depends on the age of the woman at the moment the embryo freezing was done.  With improving technology, the difference in pregnancy rates between frozen and fresh embryo transfers is negligible. 
What are your obligations with the center where you are keeping your frozen embryos?  
The center cannot extend the storage of embryos without your written consent. It is important that the center is informed of any change in contact details. If they are unable to contact you, your embryos might be removed from storage to be discarded.
In case of non-payment of the storage maintenance fees, your embryos might also be removed from storage, even if the consent to store your embryos has not expired.
What happens if you separate from your partner? 
Embryos are created from a sperm and an egg. Therefore, both partners have to individually sign a consent form specifying the terms under which the embryos are stored. Both the female and male partner has to complete a special consent form to indicate their wishes for the use of stored material. Embryos can only be used if both male and female partners agree upon their use. It is also important to specify what you want to do with the embryos in case one or both of you dies.
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