Embryo cryopreservation is an established technique whereby embryos, or pre-embryos, are frozen and stored for future use. The primary purpose for cryopreserving pre-embryos is to bank spare embryos that are not transferred during an IVF/ICSI cycle. Generally, only 2-4 pre-embryos are transferred to the recipient during an IVF/ICSI cycle. Many times there are more pre-embryos generated during an IVF cycle than are transferred to the recipient. If these pre-embryos are of good quality, patients are encouraged to cryopreserve these for potential future use.

Frozen Embryo Transfer, or FET, is the process of thawing, culturing, and transferring pre-embryo(s) to the uterus in an attempt to achieve pregnancy. The process of FET is the same as that for a transfer after a routine IVF/ICSI retrieval, except that the pre-embryos must be thawed in advance of the procedure. FET has its advantages in that the patient does not need to take expensive ovulation- induction medications and undergo another oocyte retrieval procedure. Furthermore, the uterine receptivity of the recipient can be better controlled by the physician to accommodate the pre-embryos. Since fewer medications and procedures are performed for FETs, the costs are considerably lower than those of an entire IVF/ICSI cycle. Pregnancy rates for FET at Virginia IVF and Andrology Center are comparable to those of a fresh IVF/ICSI cycle.

Pre-embryos are routinely cryopreserved at the zygote (fertilized egg), cleaved pre-embryo , or blastocyst stage. The stage at which the pre-embryos are cryopreserved depend on many factors. Such factors as the egg donor's age, the number of zygotes generated, and the quality of the pre-embryos contribute to deciding how many, and at what stage the pre-embryos should be cryopreserved. Before and during an IVF/ICSI cycle, the physician in consultation with the Virginia IVF and Andrology Center's embryology staff, will advise the intended parents on cryopreserving pre-embryos.

Freezing all pre-embryos for subsequent transfer may be advised for women who are at a high risk of developing severe ovarian hyperstimulation syndrome following ovarian stimulation for in-vitro fertilization (IVF). Cryopreserving the pre-embryos and delaying pregnancy decreases the risk of ovarian hyperstimulation syndrome. Since pregnancy rates are comparable between frozen embryo transfers (FET) and fresh transfers, this approach has been quite successful and safer for our patients at risk for ovarian hyperstimulation syndrome at the Virginia IVF and Andrology Center.

After pre-embryos are frozen, they must be specially stored and maintained at -196 0 C in liquid nitrogen tanks to keep them appropriately preserved for future use. Virginia IVF & Andrology Center can maintain storage (at a nominal fee) of your pre-embryos until such time as you choose to utilize them for a future transfer. Currently, there is no evidence that the length of time in storage affects the ability of a cryopreserved pre-embryo to survive and develop into a normal baby. Although rare, the Virginia IVF and Andrology Center has patients who have opted to bank their pre-embryos for up to 10 years and have successfully delivered babies after an FET.

The success of the thawing process can vary depending on the quality of the pre-embryo and stage of development at the time of freezing. In general, approximately 75% of all frozen pre-embryos survive the thawing process.