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Embryo Freezing (Vitrification)

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At the beginning of an in vitro fertilization treatment, a very important question which concerns doctors and couples is the number of eggs that will potentially be produced during the cycle. This information initially seemed to have been of little relevance, but it has become important. The number of eggs produced is directly related to the number of embryos that will be obtained. A large number of embryos produced offer the medical team a better selection of embryos for the transfer, increasing the success rate. It also offers better conditions for longer cultivation, blastocyst culture, minimizing the chance of embryonic loss during the cultivation.

Nevertheless, high numbers of eggs can produce a large number of excess embryos in the cycle. According to the Federal Council of Medicine, nowadays the excess embryos in the in vitro fertilization cycle can have three destinations: freezing, donating to another couple, or donating to scientific research. There exists a certain resistance from couples to the last two options that relate to donation. Therefore, freezing becomes the evident choice.

Embryo freezing has a long history within reproductive medicine, originating in the mid- 80’s, and today, it is a proven procedure already widely diffused in the human reproduction centers throughout the world. In this field, a variety of laws exists which generally changes in accordance with the country. However, in general, embryo freezing is accepted by the majority. This allows couples who produce high number of eggs and, therefore, embryos to have another chance to conceive. In the same manner, couples who succeed on the first attempt and freeze the excess embryos can return after a couple of years and use these same embryos for a second attempt.

Embryos to be frozen must go through a dehydration process, in order for some water to leave the cells. This prevents the embryos from bursting during the process. After this stage, they are submitted to computerized freezing, starting at 37ºC and within a period of two hours, reaching -30ºC, and later being stored in liquid nitrogen at -196 º C. The length of time in the liquid nitrogen seems to have little affected on the embryonic viability. Cases of pregnancy already exist after a period of 8 years of freezing. The loss of viability during storage seems to be small; however, uncertainty still exists as to the maximum period of time in which the embryos can endure.

Similar to questions related to the freezing process, the current number of procedures performed and the success rate per attempt demonstrate that this procedure offers good success rates and should be used when necessary, such as in those couples who produce a high number of embryos. Another approach would be the storage of embryos by couples who, on the contrary, produce a small number of embryos. These couples could do various cycles with small quantities of embryos and freeze them. After a few months, this “stock” of embryos could be used at one time to maximize their chances. It is a common procedure in spontaneous cycles; that is, it only occurs in the production of one egg, or in some women with very low egg production.

In general, this procedure should always be considered when starting an in vitro fertilization treatment, for chances of using it are relatively high.