What is Vitrification?
Vitrification is a rapid freezing technique which uses substances called cryoprotectants to prevent the formation of ice crystals when freezing tissues and cells. This process can be applied to human tissues and cells such as embryos and eggs (oocytes) and, in recent times, has been shown to lead to better survival of these embryos and eggs and, consequently, to improved success in assisted reproduction treatments such as IVF. Typically, vitrification protects the tissues and cells from injury during the freezing and thawing process, therefore resulting in increased survival compared to traditional freezing methods.
The Science and how it works!
Vitrification is a process that produces a glasslike solidification of living cells that completely avoids ice crystal formation during cooling and warming, allowing excellent recovery of cells for use in the IVF clinic.
The embryologist adds a cryoprotectant (a substance that is used to protect biological tissue from freezing damage) and the drop containing the embryo or egg can be cooled until it hardens like glass without any ice crystals forming.
Why choose Vitrification and what are the benefits?
Vitrification leads to improved survival of embryos and eggs compared to the older or more traditional method of “slow freezing”. This is because it avoids the ice crystal formation that occurs with “slow freezing”. This is particularly important with human eggs (oocytes) and blastocyst stage embryos, both of which contain significant volumes of fluid within which ice crystals can form. Embryo post-thaw survival rates are typically 95% and resultant pregnancy rates are on a par with those achieved using fresh embryos.
Embryo freezing is an essential part of safe IVF practice because it allows the placement of only one or two embryos in the woman’s uterus, while remaining embryos are frozen for later use – either if the first embryo transfer is unsuccessful or, where it is successful, to allow the couple have a second child at a later date. As IVF technology progresses, it benefits some couples to allow their embryos grow to the blastocyst stage (day 5 or 6). This is where vitrification is superior to slow freezing.
Merrion Fertility Clinic has been proactive in promoting elective single embryo transfer in Ireland. This involves placing just one embryo in the woman’s uterus and freezing any extra embryos. While single embryo transfer is not suitable for all couples, we have shown that, in selected couples, pregnancy rates of 40-50% can be achieved with a single embryo, and the couple will also have frozen embryos, use of which brings the chance of pregnancy with one cycle of treatment up to 60-70%. We are now performing elective single embryo transfer in over 20% of couples and our twin pregnancy rate has dropped to 14% (national average is over 25%). We anticipate that the introduction of blastocyst culture and vitrification will allow us to offer elective single embryo transfer to a wider group of our patients.
Vitrification technology also enables freezing of mature eggs with an improved survival rate after thawing and some clinics report similar pregnancy rates to those achieved using fresh oocytes. Oocyte vitrification may be recommended in two principal circumstances: (1) for medical reasons where part or all of the ovaries must be removed (e.g. endometriosis) or where treatments such as chemotherapy or radiotherapy can cause early ovarian failure (menopause) or (2) under circumstances where a woman is not in a position to conceive and is concerned about age related fertility loss. While the optimal and strongly recommended course of action is to plan a family before the age of 35, egg freezing represents an option to prolong reproductive capacity for women.
Vitrification can increase the survival rates for blastocyst stage embryos and for oocytes and is now a widely used technique worldwide with thousands of healthy babies born.
What are the disadvantages of Vitrification?
Sometimes embryos do not survive the freezing and warming process but the survival rates for vitrified embryos (95%) are still higher than the traditional freezing techniques (75%).