In short mbryo freezing is an important element of assisted reproduction. During an IVF procedure, more eggs are usually fertilized than can be transferred to the uterine cavity at one time. This aims to increase the couple's chances of a successful in vitro fertilization. Untransferred embryos are secured through freezing.
Developing embryos that are not used in a given IVF procedure undergo cryopreservation, a special freezing technique designed to preserve the developmental potential of embryos for an appropriately long time. After a period of culture in the laboratory, they are placed in special carriers along with cryoprotectants intended to remove water from them. They are then placed in a container of liquid nitrogen and frozen at an extremely low temperature. From that moment, they can wait safely for the next transfer, and the containers with frozen embryos are constantly monitored. It is worth remembering that at no stage of the procedure is it possible to destroy embryos that have the potential for further development.
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Embryos intended for transfer are thawed a few hours before the procedure, which significantly prevents the risk of damage. After removing the embryos from liquid nitrogen, they undergo the reverse process of vitrification—they are placed in decreasing concentrations of cryoprotectant and then transferred to a culture medium, where they await the moment of transfer. During this time, their metabolic functions resume before being transferred to the uterine cavity.
In a situation where a couple does not wish to use the frozen embryos later, they also have the right to donate them to a donation program.
There are two main cryopreservation techniques:
Embryo cryopreservation is considered one of the safest procedures throughout the entire IVF program. The survival rate of embryos subjected to this process is very high, exceeding 90%. Oocyte survival may be slightly lower due to the fact that these cells are more sensitive than embryos. The effectiveness of transfers using both fresh and frozen embryos is comparable, and cryopreservation itself should not affect its final outcome. The storage time of embryos also has no effect on this—a case of a healthy child born from an embryo frozen for approximately 20 years has been recorded worldwide.
However, other factors are key, such as:
Freezing embryos also has additional positive aspects, as this process can significantly reduce treatment costs; moreover, a patient undergoing a frozen embryo transfer does not need to undergo hormonal ovulation stimulation and ovarian follicle aspiration again.
