As with sperm and eggs, freezing embryos at low temperatures allows them to be put to further use. When embryos are frozen, they are preserved in optimal conditions for implantation.
Until recently, embryo vitrification required an embryo freezing procedure that slowly cooled the cells to prevent the formation of ice from the water inside them. But implantation rates were much lower than those achieved with fresh embryos.
Today, Assisted Reproduction specialists have at their disposal a new, more advanced method known as embryo vitrification, which offers greater effectiveness thanks to increased embryo survival and a higher rate of implantation, resulting in better pregnancy rates.
Definition of embryo
The zygote, the first stage of human life, is born from the union of sperm and egg into a new cell with a nucleus and 46 chromosomes. When the first cell division occurs from this union, the embryo is created.
The embryonic phase lasts until week 8 of pregnancy, and is characterized by intense cellular changes in which the embryo divides its cells successively. Normally, there are certain patterns of division that allow us to detect whether an embryo is of good quality.
On day five of gestation, the embryo is called a blastocyst, at which time it adopts a certain shape. It is not until 7 or 8 days that embryo implantation occurs naturally.
The earliest embryos and those in the blastocyst stage can be vitrified for later implantation thanks to advances in fertility techniques.
The freezing of oocytes requires a different process, since they have not been fertilized and will need, when they are going to be used, a process of sperm microinjection (ICSI) prior to implantation.
Differences between embryo freezing and embryo vitrification
Embryo cryopreservation has evolved considerably in recent years. Unlike classic freezing, embryo vitrification cools the cells incredibly quickly. In the past, they were frozen at a slow rate of about 0.3°C per minute to try to prevent the water in and around the embryo from forming ice crystals.
Embryo vitrification, on the other hand, rapidly cools the cells at a rate of more than 15,000°C per minute, so that it could be said that there is no time for ice crystals to form, but rather a kind of gel is formed that does not damage the cells.
Success rate of embryo vitrification
This technique achieves a lower number of damaged embryos and, therefore, a higher implantation rate. With the old freezing method, one in three patients became pregnant, while with vitrification the success rate is over 50%. In addition, since there is a greater chance of embryo implantation, fewer embryos can be transferred, thus reducing the risk of multiple pregnancy without making the treatment less effective.