Embryo freezing is an important part of the IVF process. Patients who have additional good quality embryos can freeze them for future use. These embryos provide a second or even a third opportunity for pregnancy without undergoing another ovarian stimulation and retrieval.
Scientists can freeze embryos that meet developmental criteria for appearance and rate of growth at any of several stages of development.
There are 2 ways to freeze embryos.
Slow cooling is one method. With this method embryologists place embryos into special freezing solutions. After that, with the use of a computer, the scientist slowly decreases the temperature of the embryos. Then, they store frozen embryos in liquid nitrogen (at -196°C or approximately -400°F), or sometimes, in liquid nitrogen vapor.
Vitrification is another technique for freezing embryos. In this ultra-rapid freezing method, the embryologist places embryos into special solutions. Then, they place them immediately into liquid nitrogen. They store the embryos same as in slow cooling. The method used to freeze embryos dictates how the embryos must be warmed or thawed. Not all embryos survive the freezing/thawing procedure. Sometimes doctors cannot find any embryo after freezing.
Specialists can tranfer embryos into patients whose cycle has been synchronized with that of the stage of the frozen embryo. Alternatively, they can transfer embryos during a “natural” cycle. Moreover, they can store embryos indefinitely without a compromise in their quality.
A Danish study published at ESHRE showed that there is concern about congenital malformations in babies born after thawing of freezed embryos. Moreover the same study proposed that maybe all embryos should be frozen and not transferred, given that the conditions under which a fresh transfert occurs are not so normal due to high maternal hormone levels during stimulation.