Pregnency rates and increasing with recent improvements in embryo freezing and thawing (embryo cryopreservation), which has been in use for over 25 years. Today, a technique called Vitrification (fast freezing) is used instead of the older technique, slow freezing. Thanks to cryoprotectants, embryos can be kept in sleep mode in liquid nitrogen in 196?C. When transfer date is due, they are taken out of nitrogen, the procedure is reversed and then the embryos are prepared for transfer. In our centre usually 3rd and 5th day embryos are frozen. Statistics show that, the better the quality of the frozen embryo, the higher chances of success in retrieving and bringing embryos back to life; thus, the higher chances of pregnancy.
The possibility of freezing, thawing and transferring embryos, provides couples with a much cost efficient chance of trying to get pregnant. Besides, there will be no need for long-term medication. Frozen/thawed embryos provide an easier and shorter period of treatment, more efficient costs and almost the same rate of success in getting pregnant as in fresh embryo transfers.
If there are enough and good quality embryos, with the consent of the couple, embryos are frozen. The first advantage of this is that it allows embryo transfer without any need for stimulation of the ovaries if there is no pregnancy in the first treatment. Thus, there is no need for medication and egg retrieval. It is known that with older age, the quality of the eggs is reduced. A woman who has had her embryos frozen, can use them a few years later.
Chances of pregnancy with frozen/thawed embryos are as good as with freshly transferred embryos at a qualified centre. Thus, freezing and thawing should be handled with most care.
Cryoprotectants used are arranged to allow increasing concentrations. With the help of such liquid agents, the water inside the embryo is slowly replaced with material that do not expand when frozen and thus do not rupture the cell.
This procedure is followed in such a way to avoid any damage to the embryo, at a certain temperature and time sequentially. When time is up, the tube or rod containing the embryos is placed into the freezer. The quality and capacity of this medium is also important in maintaining the freezing.
The program to freeze is determined by the embryologist and it is saved/uploaded to the equipment, and the program is started accordingly. In principle, the temperature is gradually decreased to -30?C. After that, it is cooled down to -150?C, faster, and the frozen embryos are placed into the storage medium which contains liquid nitrogen and they are kept at -180?C.
When thawing no specific machinery is used. Chemicals used in freezing are introduced in a reversed order this time. When embryos reach room temperature, they are taken into the densest liquid. By constant and careful monitoring of the embryos, when they reach 37?C, which is the body temperature, they are put into the warm and humid incubator containing gas.
Depending on the day when and number that were frozen, they can either be transferred on the same day or observed for a few days to select the healthy ones that keep dividing. Usually, this procedure is followed. Division and quality determines the chances of pregnancy.
Freezing and thawing is a traumatic process for the embryo. Embryos with low stamina and constitution may receive more damage than others.
If there are no healthy embryos, or if there is no growth or cell development while monitoring in the laboratory after thawing the embryos, the transfer is cancelled.