Cryopreservation of embryos maximizes the chance of successful pregnancy with any IVF treatment cycle. Prior to the availability of embryo cryopreservation, IVF centers had to deal with “excess eggs (oocytes) and embryos” without the ability to save, or preserve them. They were forced to “selectively” fertilize only a few eggs to avoid “excess” embryos, but would run the risk of wasting normal eggs that were not fertilized. Alternatively, if all eggs obtained from an IVF cycle were exposed to sperm, an excess number of embryos might have resulted with pressure of transferring more embryos than recommended, resulting in multiple pregnancies (i.e. twins, triplets, or greater). If the embryos could not be cryopreserved, couples may have been forced to discard excess embryos, creating some potential ethical or religious conflicts.
Embryo cryopreservation during IVF treatment, allows for all of one’s eggs recovered that cycle, to be exposed to sperm. Because all oocytes can look ‘normal’ after retrieval, exposing all of the oocytes to sperm increases the chance of having higher quality embryos available for transfer. Not only does embryo cryopreservation maximize the chance of being able to transfer embryos of the highest quality through the process of selection after fertilization, but it also gives a couple the opportunity to freeze extra embryos for use in the future, if they are of good quality. Use of cryopreserved embryos in the future avoids the need to repeat stimulation of the ovaries with injectable medications, since the embryos have already been created. Success rates with frozen embryos have been near, or equal to fresh IVF treatment cycles at many IVF centers in recent years.
Cryopreservation of embryos can be done at nearly any stage of development.
The most common stages are:
- Pronuclear freezing
- Day 3 embryo freezing
- Day 5 blastocyst freezing
- Oocyte or egg freezing can also be done