IVF, ICSI, and Egg donation treatment often generate surplus embryos. These ‘spare’ embryos are often of good quality and can be kept in storage for future use.
Now the question arises, why these surplus embryos are created? In an IVF cycle, all the related treatments of egg cell production are executed to stimulate the ovaries to release multiple high-quality eggs. Most IVF clinics aim to fertilize each of the eggs in order to have multiple embryos to select from. But all the embryos produced do not have the same capacity or potential to develop. As the embryos grow in the laboratory, IVF Consultants get to select the best quality embryo for implantation. In some of the IVF cycles, multiple embryos are implanted. The ones that have the potential to make healthy babies but are not used in the first implantation are frozen rather than discarded. These embryos become viable once they are thawed. These embryos have a great possibility of achieving successful pregnancies in the future without involving the process of ovarian stimulation.
It is not necessary to freeze the spare embryos. However, it is recommended for couples who have had previous experiences of failed IVF cycles. This gives them the opportunity of a pregnancy in the future, in case the first IVF cycle does not work for them. This saves both time and money for the parents, as they do not have to go through the entire treatment once again.
We usually come across the question of how many embryos can be frozen and stored. As a matter of fact, every patient is not fortunate enough to have embryos suitable for freezing. The excess embryos are cultivated in the laboratory for nearly 6 to 7 days once the eggs are collected. This investigation helps in finding the development of the embryo to the blastocyst stage. Hence, this procedure is known as the ‘blastocyst culture’. This helps in selecting the blastocysts with greater potential to develop into a healthy pregnancy and successful implantation. The embryos with the potential to develop into good quality blastocysts are frozen once they are found to have the capacity of surviving the freeze and thawing process.
Most of the embryologist batch a few embryos together. If there are day three embryos they may freeze three embryos together while with blastocysts they may freeze two embryos. If parents are strictly against having twins they are recommended to vitrifying just one embryo. It allows the embryologist to thaw just one embryo and transfer to the surrogate mother or to the intended parent.
If parents are still unsure how many embryos they are willing to transfer, they are still suggested to ask for vitrifying just one embryo per straw. It is not recommended to have two or three embryos together, thaw them, transfer just one and refreeze the remaining embryos. It will significantly decrease the quality of the embryos.
The next thing intended couples are curious about is the possibility of any decrease in the quality of the embryos that have been frozen for a long period of time. The embryos are generally vitrified and kept frozen to be used for future attempts. Vitrification is one of the highly rapid freezing processes used by most IVF clinics that help to achieve higher rates of embryo survival. This method decreases the development of ice crystal damage of the embryos that can happen in other freezing methods.
The embryos that are selected to be vitrified are placed in a ‘cryoprotectant’. Those are inserted into a ‘straw’ and are labeled with the unique details of the intended parent/egg donor. These straws are then kept in large storage tanks that are filled with liquid nitrogen at -196Cº. Selected embryos will be frozen during different stages of their development:
1. Day 1 (pronuclear stage)
2. Day 2/3 (4-8 cell stage)
3. Day 5/6 (blastocyst stage)
The embryo analysis test that has been conducted before the selection of the embryos to be kept under vitrification helps in ascertaining the day of freezing. However, it is often recommended to freeze embryos at the blastocyst stage to get better results and higher rates of embryo survival.
The procedure of implanting embryos after thawing has been used since 1983. There is absolutely no problem in thawing frozen embryos and using them. The survival rate of the embryos is almost 85%. The assisted conception treatment includes this vitrification and thawing method of embryo storage as an important tool of diminishing the cost and time of repeated egg retrieval.
The cryopreserved embryos can be stored for as long a period as you want. The duration can extend 10 years or more. There is no deterioration in the quality of the embryo due to a prolonged vitrification. The couples of egg donors who have cryopreserved their eggs through vitrification are required to renew their consent contract with the IVF clinic they have kept their frozen embryos with.
The rate of survival of the embryos after the thawing process is nearly 85%. There are many instances where the embryos are cryopreserved for more than 15 years and have been successfully used by other couples facing infertility issues.
The thawing procedure of the embryo is very simple and takes only a few minutes. The embryos are first taken out of the frozen storage and then thawed properly. In particular cases, the embryos are left for a day or two after the thawing is over. This time is invested to expect some growth in the embryo. This procedure is done particularly when the embryos were below the 4 cell stage at the time of freezing.
Multiple births are considered as one of the greatest risk associated with fertility treatments. This also carries a risk to the health of the mother as well as the unborn baby. Hence, the important aspect of using frozen embryos is how many embryos will be used for the implantation? In case the mother is pregnant with twins or triplets, she is more likely to deliver babies who will be premature and below normal weight. This is why, in almost all the cases, there is a single embryo that is thawed and implanted. Some patients are however eligible for the double thaw and transfer. As a matter of fact, IVF consultants and expert discuss the number of embryos to be thawed with the aspiring parent and accordingly plan the treatment. There are multiple things associated with such selection. The health and test report of the mother is very important to be evaluated while making such decision. At times aspiring parents want to have twins or triplets and they can discuss this with the IVF consultants they are working with. Since it is a very crucial decision for both the intended parents and the IVF consultants is handled very carefully.
The implantation of frozen embryos results in absolutely normal pregnancy in almost all of the IVF cycles. It is very similar to the natural and HRT stimulated FET cycles. The intended parents are usually educated about the entire procedure before signing the contracts. They like to see the statistics related to this vitrification procedure and once assured, they move ahead and make their final decision.