Frozen Embryo Transfer Cycle refers to the process of cryopreserving embryos and transferring them into a woman’s uterus that has been prepared for IVF.
What is Embryo Freezing?
The conventional IVF procedure, which utilizes fertility medications to stimulate ovulation often results in excess embryos. Since the risk of multiple pregnancies increases with the number of embryos transferred, many couples are left with more embryos than necessary or more embryos than can be transferred by law in some countries. In some countries, like the UK, the maximum number of embryos that can be transferred is three. These spare embryos can be discarded, used for research, or they can be frozen and cryopreserved for later use by the same couple or another couple wishing to use a donated embryo.
Advantages of Natural Cycle IVF
No fertility drugs are used for ovarian stimulation, reducing the risk of side effects such as OHSS.
Natural Cycle IVF treatment can be repeated in consecutive months. Women who have an unsuccessful traditional IVF treatment must wait three months before attempting a second cycle. Natural cycle IVF is less expensive as couples do not pay for fertility drugs.
Disadvantages of Natural Cycle IVF
Only one egg is fertilized reducing the chance of successful fertilization. Success rates are lower than fertility drug stimulated IVF treatment.
Woman who are at risk of developing ovarian hyperstimulation syndrome, following ovarian stimulation for IVF treatment are advised to freeze their embryos for consecutive transfers. In some cases, fresh embryo transfer fails, and “spare” embryos can be cryopreserved for a second or third trial. Cryopreserved embryos are available for donation to unfertile couples. In fact, some countries mandate that all embryos resulting from donated eggs be cryopreserved and quarantined for a period of six months until all donor screening tests are complete.
Frozen embryos are as respectable as fresh embryos, meaning that pregnancy rates are at an equally high level. There is no higher risk of abnormalities with frozen embryos than fresh; therefore patients are often encouraged to choose the more cost-effective route of freezing their embryos rather than discarding them. This also guarantees that in the event that the first embryo transfer fails, or pregnancy is not carried out to term. Using frozen embryos, which can be stored for up to several years, is a much less expensive alternative to starting a new cycle.
Embryos can be stored in groups of one or more. With any living tissue, the cells of embryos contain water, which must be removed prior to freezing to prevent ice crystals from forming and causing the embryos to burst. The embryos are gradually mixed with a cryoprotectant fluid that does not form ice crystals, and located in a plastic straw or a glass vial. The mixture is stored in liquid nitrogen at a very low temperature using a specialized programmable machine. Temperature is crucial since embryos are subject to metabolic change.
How are Embryos Thawed?
During the thawing process, the frozen embryos are removed from the vial and thawed to room temperature. The cryoprotectant fluid is gradually removed and diluted with water. This process must be done very diligently as the embryo can burst if the water is rushed into the cells. After the embryos are brought to room temperature, they can be transferred to the recipient mother.