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Alongside with semen freezing, cryopreservation is one of the key components in ART. “Surplus” oocytes obtained from a single collection can be stored for later use. Thus, reducing the costs and risks of hormone stimulations associated with multiple oocyte collections.
Although fertility specialists used cryopreservation with a slow-freezing protocol for achieving pregnancies back in 1986/1987, the method is not very effective nowadays within the IVF laboratories. The reason is that the method may directly affect the oocytes or have an indirect impact on subsequent embryo development. As with the slow-freezing protocol, the success rate of successful thawing of oocytes averages 74-90% and depends heavily on the expertise of the IVF center.
Vitrification (ultrafast freezing) of human oocytes represents a breakthrough in the reproductive sciences and the practice of assisted reproductive medicine. Since the main damaging factor for human egg cells in the freeze-thaw process is the formation of ice crystals, it does not happen during vitrification of human egg cells. Substances simply become amorphous without the formation of ice crystals, which minimizes the likelihood of human egg cell damage.
Both survival and implantation rates appear to be higher than those of unfertilized human egg cells when using slow freezing protocols. Thus, the average rate of successful thawing of vitrified human egg cells is 84-99% on average, the frequency of cleavage of human embryos is about 87%, and the rate of blastocyst formation is about 50%. For many years, Surrogacy Ukraine has been actively offering a vitrification method for freezing both human egg cells and embryos.
There are both medical and social reasons for cryopreservation of human egg cells: young women undergoing cancer treatment; low ovarian reserve with a weak response to ovarian stimulation; forthcoming surgical interventions on the ovaries; sudden absence of a partner on the day of IVF procedure; professional activity or marital status (single). Cryopreserved egg cells are stored in an IVF laboratory in liquid nitrogen at -196° C.
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The limited life span of human spermatozoa requires strict coordination of simultaneous formation of both sperm and oocytes, which in some cases may be inconvenient or even impossible. For this reason, some valuable studies have been conducted to prolong the life span of sperm by cooling cells. In 1953, the first woman’s healthy pregnancy was reported as a result of the use of cryopreserved human sperm.
There are both medical and social reasons for sperm cryopreservation: absence of a partner in a day of fertilization during egg fertilization; individual variability in sperm quality; fertility preservation in men: vasectomy, radiation therapy, or treatment with cytotoxic drugs; upcoming surgical interventions on the testicles; preventing the transmission of diseases through semen; inability to get fresh ejaculate in a day of oocyte puncture; donor sperm bank creation.
Sperm cryopreservation has brought a revolutionary change to assisted reproduction. There are two effective methods: slow freezing and vitrification. Frozen sperm are stored in liquid nitrogen, where they remain inert as long as they are at -196° C. There is no evidence of additional risks of birth defects or chromosomal abnormalities after using cryopreserved sperm – this is a safe way to preserve male gametes.
