Oocytes / Embryos / SPERM Cryopreservation
All kinds of donor cells, oocytes and sperm are now actively used in the programs of assisted technologies on overcoming infertility. As a result of superovulation the number of embryos obtained from one patient is much more than that required for the transfer. To solve all these problems, the technology of preserving the donor’s oocytes/sperm or the couples’ embryos is required.
Cryopreservation technology in reproductive medicine was first applied to sperm. Italian physician Mantegazza in 1866 wrote a monograph on maintaining the ability of bulls and horses’ sperm to fertilize after freezing to -15°C. Mantegazza was the first to propose to create a bank with frozen semen of soldiers who could be killed in heavy war fights. In 1954, the first child, conceived by the artificial insemination of frozen and thawed semen, was born.
The first successful attempt to freeze and thaw mouse embryos was in 1972, the first pregnancy by the embryo after cryopreservation was obtained in 1980. The most difficult task was the cryopreservation of oocytes, but in 1986 the embryos from oocytes were successfully derived and the pregnancy was achieved by slow freezing and thawing. But the real breakthrough was the technology of rapid or instant egg freezing. The conventional technique of freezing envisages that the cell temperature is reduced by 1 degree Celsius per 1 second and the risk of ice crystal formation in the oocyte, which damages like a razor its genetic material, DNA, is high and only 10% of oocytes survive defrosting. Meanwhile instant freezing or vitrification (from the Latin word “vitro” — glass) cell temperature is reduced for 1 second to 100 degrees Celsius and the water in the cell does not crystallize, but turns into a kind of gel, unable to damage the genetic material. The vitrification method has been successfully used since 1990 and allowed for keeping up to 96% of viable eggs after thawing.
Using cryo-technologies allows for creating banks of donor sperm and eggs, preserving the «excess» embryos in IVF cycle for the birth of the second child or using it without the ovulation induction in the future if the first attempt wasn’t successful. Cryopreservation enables you to save the embryos for delayed transfer in case of the ovarian hyperstimulation syndrome. Saving oocytes taken in advance from women, who will undergo chemotherapy, enables them to have healthy children in the future or preserve quality eggs at the age of 25-30 years, to get an opportunity to have a healthy baby in their forties.
Cryobanks are large vessels, flasks of liquid nitrogen at the temperature of -196 degrees Celsius, which keep the labeled containers with thin glass tube-straws. These are where embryos are kept. Sperm and oocytes are kept in a similar way. At this stage it is believed that the frozen sperm or oocytes can be stored without the quality loss up to 10 years.