What is the vitrification or freezing of embryos?

The freezing of both ovules and embryos is done by an ultrafast freezing technique called vitrification. This method has many advantages with respect to slow freezing, which was the technique used until the discovery of vitrification. Among them, the high survival rates after devitrification and freezing time stand out.

The cryopreservation of ovules and embryos is allowed by Spanish law and is a basic tool in assisted reproduction. Thanks to it, embryos can be preserved for later use, both for own treatment and for donation to other couples or research projects.

Below you have an index with all the points that we will discuss in this article.

Index

What is the vitrification or freezing of embryos?

• 1. When to vitrify embryos
• 2. Vitrification technique
• 3. Defrosting or devitrification
• 4. Success of the treatment
• 5. Price
• 6. Questions from users
• 6.1. Can type C embryos be frozen?
• 6.2. What is the difference between freezing and embryo vitrification?
• 6.3. Can I freeze embryos in Social Security?

When to vitrify embryos

The embryos produced in the in vitro fertilization laboratory (IVF) can be vitrified by numerous circumstances:

• For not being able to make the transfer in the same cycle in which they were created.
• After a cycle of IVF in which remaining viable embryos remain after the transfer.
• To preserve fertility, as an alternative to the vitrification of ovules.
• For having to wait for the results of the biopsy in a PGD.

The embryos remain frozen at -196 ° C in liquid nitrogen tanks until the woman or couple decides to use them. They can be preserved for an indefinite period without losing the characteristics they had at the time of vitrification. Thus, embryos can be used months or years later to look for a pregnancy.

It is important to keep in mind that embryos must have a minimum quality to be able to withstand the processes of freezing and thawing. Therefore, those embryos that do not develop well or that show signs of degeneration do not vitrify.

Vitrification technique

Vitrification is an ultrafast freezing process in which cryoprotectants are used, molecules that protect the internal structures of the embryo from low temperatures. These molecules replace the aqueous liquid inside the cell.

The process to follow is the following:

The embryos are passed through a series of media with an increasing concentration of cryoprotectants that dehydrate the cells.

The embryos are placed in a support system for freezing. The most common is the Cryotop.

The support system is introduced with the embryos in a small bucket with liquid nitrogen.

A cap or cap is placed on the support in which the embryos are.

The cap is transferred from the tank to the liquid nitrogen tank.

After these steps, it is achieved that the embryos go from the culture temperature (37 ° C) to the freezing temperature in liquid nitrogen (-196 ° C).

Embryo vitrification process

Defrosting or devitrification

To be able to use frozen embryos it is essential to devitrify them. To do this, they are removed from the liquid nitrogen and passed through several media with decreasing concentrations of cryoprotectants.

This is how cell rehydration is achieved, so that the cryoprotectants are replaced by water. It is very important to respect the times and carry out the devitrification correctly, since otherwise the cellular structures of the embryo could be damaged and the embryo may not survive.

Generally, embryonic devitrification is performed on the same day of the transfer, with a few hours difference to be able to check the status of the embryo. Otherwise, the transfer is done the same as with fresh embryos.

Treatment success

The treatments with fresh ovules present pregnancy rates slightly higher than those in which embryos are used that have been vitrified. Even so, cryopreserved embryos are able to continue their normal development, implant and give birth to a healthy baby.

According to the statistical report of the Spanish Society of Fertility (SEF) of 2014, there is a 36.6% of pregnancies for each transfer of fresh embryos and 34.4% for each transfer of frozen. These data correspond to embryo transfers from the patient's own ovules, not from a donor.

This rate does not take into account embryos that do not survive the process. Therefore, although there is little difference because most embryos survive, we must bear in mind that pregnancy is achieved in 32% of cases for each thawing.

That pregnancy is achieved after a transfer of cryopreserved embryos will depend on the following factors:

• The survival of embryos after thawing
• Embryonic quality and its capacity for development
• The receptivity of the endometrium at the time of transfer

The survival rate of embryos after devitrification is greater than 80% and embryos usually survive intact. For this, it is essential that the laboratory has a good vitrification program and that the laboratory personnel have the adequate preparation to carry out the process.

Price

Embryo freezing costs between ? 300 and ? 600 in Spain, depending on the center in which the process is carried out. To this must be added the price of maintenance, since conserving embryos in liquid nitrogen has a cost for the clinic of assisted reproduction.

The maintenance of the embryos is paid, usually, annually and in some centers the first year is included in the cost of vitrification. The maintenance can be between 400 and 600 ? per year.

Also, the devitrification and transfer of frozen embryos costs about ? 700-2000, to which we must add another ? 200-300 of the medication to prepare the endometrium.

In Assisted Reproduction ORG you can get the first free visit and a reduction in price thanks to the agreement we have with many Spanish clinics. In the discounts section you will find all the information, with some discounts that also include 1 year of maintenance, by clicking on the following links:

• See discounts for embryo vitrification.
• See discounts for the transfer of frozen embryos.

Questions from users

Can type C embryos be frozen?

Yes, it is possible to free embryos of quality C. They are considered to have a lower implantation capacity than embryos A and B, since they have not followed an adequate development or present any sign that may compromise their viability to some extent.

Since these embryos do not have such good quality, they are usually left in culture to observe their evolution one or two more days. If they evolve well, they can be vitrified, but if they stop developing, they should be discarded because they are not viable for transfer to the uterus.

What is the difference between freezing and embryo vitrification?

Embryo freezing is a procedure used before the discovery of vitrification, which consisted of a slow and progressive process that could take about 2-3 hours. It did not have good survival rates due to the damage that was produced to the embryo by the formation of ice crystals. Although it was possible to freeze early embryos, the blastocysts did not survive.

In vitrification, however, the procedure is very fast, a few minutes, and it is possible to freeze blastocysts. By this procedure embryonic damage is not produced, since ice crystals do not form.

For more information on slow freezing and vitrification, access to this article: Freezing and vitrification of gametes and embryos.

Can I freeze embryos in Social Security?

Yes, as long as you can get an in vitro fertilization treatment in Social Security, you can freeze the obtained embryos. Also, in cases of cancer, it is an alternative to ovule vitrification.

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