Modern medicine uses various assisted reproductive technologies (ART) to increase the chances of successfully conceiving, carrying and giving birth to a healthy baby, including in people with impaired sexual function. One of them is cryopreservation of embryos – a method of preserving them through ultrafast freezing. It is particularly common during IVF, after which a woman is left with surplus biological material (eggs) that can be used in the future. However, despite the prevalence of this technology, there are still many myths surrounding it, due to which not all women agree to its use even for medical reasons. Let’s find out how true they are, and what are the advantages and disadvantages of this technique.
Cryopreservation of embryos: peculiarities of the technology
The first thought about preserving the genetic material of parents for successful future use dates to the 18th century – in 1768, Italian naturalist Lodzaro Spallanzani first conducted experiments on freezing sperm with ordinary water ice, as a result of which he found that after thawing, sperm retain their fertility. Later, in the late 19th century, Italian physician Paolo Montagazzi first suggested the idea of preserving frozen sperm of soldiers going to war to preserve their genes in case of possible death. And shortly before the Second World War, German scientist F. Janel suggested preserving male semen at ultra-low temperatures in liquid nitrogen.
The first medical experiments on the cryopreservation of germ cells began in the mid-20th century. In 1953, a healthy child was born from frozen sperm, and in 1972 an experiment on the transfer of a frozen mammalian embryo was a success. The real breakthrough was in 1983, when a pair of monozygotic twins was born in the Netherlands using cryopreserved embryos. Since then, the technology quickly gained medical recognition and began to be used in reproductive clinical practice.
In its most general form, cryopreservation of embryos is the freezing of embryos for long-term storage. However, experience has shown that the water in the cell cytoplasm forms ice microcrystals during freezing, which damage cell structures, leading to embryo death. This problem can be solved in two ways:
Slow freezing. Embryos are immersed in a cooler and cooled to 198° C for 2 minutes. The gradualness of this process reduces the risk of ice microcrystals forming and damaging cell structures.
Ultra-rapid freezing. This process is also called vitrification (vitrification) – cryopreservation of embryos is performed by cooling them in liquid nitrogen at a speed of 2500 degrees Celsius/minute. That is, it reaches a temperature of -198 ° C in just a few seconds. The water bypasses the crystallization stage and immediately enters the vitreous solid state.
It is the second method that is the most demanded today in medicine due to the higher survival rate of embryos. Of the embryos frozen by the rapid method, 94% retain viability after defrosting, while in slow freezing the figure is slightly lower – 88%.
An important milestone in the development of embryo cryopreservation (vitrification) technology was the discovery of cryoprotections – substances that prevent the formation of ice microcrystals in cells. Initially, they were used to freeze organs before transplantation, but today they are actively used in reproductive medicine.
Cryopreservation of embryos takes place in several stages:
PR equilibration. This is a preparatory stage, the purpose of which is to replace the water in the embryo cells with a cryoprotectant, which is ethylene glycol and dimethyl sulfoxide. For these substances to completely displace water, embryos are placed in them for 15 minutes. Then, the embryos are immersed in sucrose, which acts as a non-penetrating cryoprotectant.
Freezing. Embryos “soaked” in cryoprotectants are placed on a carrier – a polymeric or glass tube. It can be open, maintaining contact between the cryoprotective solution and liquid nitrogen, or closed, completely isolating the embryo from the cold carrier. An embryo “packed” in this way is placed in a cryopreserve with liquid nitrogen, where it is cooled to -198°C for a few seconds.
Frozen embryos can be stored in cryobanks indefinitely – in clinical practice there are cases of successful human births from embryos whose “age” was several decades.
In addition to freezing, thawing plays an important role in preserving the viability of the biomaterial. This procedure also takes place gradually and involves several stages:
- placing the embryo in a solution of sucrose – in it the frozen cryoprotectants begin to thaw gradually without damaging cellular structures;
- decreasing the sucrose concentration to replace the cryoprotectants with normal water;
- “washing” the embryos in a medium that does not contain protectants for their final removal from cellular structures.
After thawing, the biomaterial is placed in an incubator for several days to germinate to the blastocyst stage. Then the cultured embryos become ready to be transferred into the woman’s uterus. Ask more at International Surrogacy Agency Delivering Dreams.