Freezing eggs is a good way to ensure your fertility in the future. It is indicated for women who for economic or social reasons must postpone their maternity and for patients who are going to receive medical treatments that may damage the oocytes. This technique represents a great revolution in assisted reproduction.
What does oocyte cryopreservation consist of?
Oocyte cryopreservation is the freezing of the female gamete with the intention of using it later. The technique must ensure that the gamete does not lose its fertile potential, that it is capable of being thawed later, to give rise to embryos that are viable and that give rise to normal pregnancies and healthy newborns.
When is this technique indicated?
This technique opens a window of hope for the fertility of many women. The first indication is for those patients who for social or economic reasons have to postpone their desire for motherhood and want to safeguard their fertility by freezing oocytes that will later be useful. It is also especially indicated for patients who will later receive medical treatments that could damage the oocytes, and before they are damaged, they can be frozen for later use. This technique also opens up the possibility of creating oocyte banks that will be very useful both in oocyte donation programs and in non-reproductive cloning programs for cell therapy and tissue therapy.
How is oocyte cryopreservation carried out?
There are two procedures for oocyte freezing, slow freezing and ultra-rapid freezing or vitrification. Vitrification is currently used, which consists, in a first step, of exposing the oocyte to a hyperosmolar solution with which we manage to dehydrate it and subsequently an ultra-rapid freezing. These two procedures avoid the formation of intracytoplasmic crystals that could damage the oocyte.
What risks can we find in oocyte cryopreservation?
The risks derive from the technical procedure used. We have mentioned that the oocyte has to be subjected to a hyperosmolar solution for dehydration and it is known that these solutions can cause damage to the oocyte, as can the freezing process itself, which can also cause damage to the oocyte. In other words, we have the toxic effects of the cryopreservative substances used and the phenomenon of vitrification itself. The best known damages are those that occur at the meiotic level and those that occur in the cytoplasmic or oocyte corpuscles. Recent work has shown that with the new cryopreservation and vitrification techniques these damages are no longer occurring.
What results can be expected with this technique?
At the beginning, the doctors who used these techniques were very cautious; there was not enough evidence about the nature of the pregnancies that were going to be achieved using devitrified oocytes. In recent years we have been able to see that oocyte devitrification results in a very high oocyte survival rate, of the order of 97%, fertility rates, implantation rates, pregnancy rates and “baby at home” rates, quite similar to those that occur with fresh oocytes. That is why this technique has been an important advance in all assisted reproduction programs.