Efficiency of cryogenic preservation was known during ancient times. With the help of cold people kept yield e seeds. The main push for prompt development of cryogenic preservation in the sphere of reproductive technologies became the first successful result on IVF.
With the help of cryogenic preservation sperm and embryos can be stored practically for an unlimited time. Thus viability of cells is completely kept. In the medical literature there is data that demonstrates pregnancy arose at implantation of the embryo stored during 12 years.
The program of freezing embryos is applied in the sphere of associated reproductive technologies since 1982. The first child-after-embryo-transfer was born in 1984. After embryo transfer the probability of occurrence of pregnancy makes 10-15 %.
Procedure of embryo transfer is based on technique of IVF. Procedure preparation of embryo transfer consists in notch coating of an embryo. At cryogenic preservation coating of an embryo is condensed; therefore after thawing an embryo and coating make cuts. As hormonal therapy medical products for preparation of mucous membrane of the uterus to embryo transfer are appointed. These preparations contain natural female sexual hormones which in natural conditions cause changes of mucous membrane of the uterus.
Then the second phase of menstrual cycle begins. The given medical preparations prepare the uterus for implantation of an embryo. In the middle of menstrual cycle the mucous membrane of uterus reaches optimum thickness and structure. The final stage is thawing and embryo transfer. Embryo transfer occurs under the control of ultrasonic. In some cases procedure embryo transfer occurs under of narcosis.
At carrying out of IVF there can be formation of 2-5 embryos. In the uterus, doctors place 1 or 2 embryos. In case if the staying embryos have no defects, they freeze. Due to this method, at unsuccessful implantation of an embryo there is an opportunity of recurrence of procedure. In this case thawing and embryo transfer which have been earlier frozen occurs. Embryos at the stage of the zygotes, two, four, eight cells and blastocyste are subject to freezing.
Freezing of embryos is made with the help of two different technologies: method of slow freezing and method of vitrification. Vitrification is the new method, however many scientists mark his high perceptivity. The method of vitrification is safer for embryos. At use of the given method it is damaged no more 10-12% of embryos.
Storage of embryos is carried out in the special marked plastic tubes. These tubes are placed in capacity with liquid nitrogen. The temperature in capacities is supervised by special gauges. Maintenance of constant temperature conditions in capacities with liquid nitrogen is one of obligatory criteria of preservation of viability of embryos. At sharp fluctuations of temperature; viability of embryos is considerably reduced. In this case the probability of occurrence of pregnancy is also sharply reduced.