Cryopreservation
Cryopreservation allows medical professionals to store eggs, sperm? and embryos. This is commonly performed as part of the IVF cycle, since often many embryos are produced, and they need to be stored. The freezing of the eggs, sperm or embryos is now quite successful, in particular for sperm and embryos.
Scientists at the COGI conference discussed how this technique could also have positive effects on the IVF cycles for patients with PCOS. It would allow the stimulation cycle and the re-implantation? cycle to be separated. On one cycle the woman would have the ovarian stimulation, but the embryos are immediately frozen and re-introduced the following cycle when her hormones are more in control.
With women leaving child bearing until later in life, cryopreservation (freezing of the egg) could become a very attractive option. However, the technique still needs to be optimised: fresh eggs give better results than frozen eggs at the moment.
This technique is not recommended to a young woman who needs cancer therapy if she has already has a partner. She would be encouraged to freeze embryos given the lower success rate of egg (unfertilised egg) freezing compared to embryo (fertilised egg) freezing.
At the moment, a cycle of IVF with embryo freezing offers them the best chance of having a baby later when they wish to start their family. Egg freezing can be considered if the woman is not in a stable relationship, and in some instances freezing of embryos with donor sperm can also be suggested.
Possible reasons for the reduced IVF/ICSI success rates using frozen eggs rather than frozen embryo.
Scientists have been working on egg freezing for over a decade, however the success rate is still unsatisfactory. The reason for this is that the egg is much more fragile than the embryo. Given that the ovocyte (egg) is in the middle of meiosis (a kind of cell division), the cell is very vulnerable to stress and freezing is one of these stressful events which can cause damage. Some evidence indicates that the zona pellucida (shell/membrane) is harder after the freezing, which makes fertilisation? harder and possibly early cell divisions of the embryo too.
Egg freezing may still offer real value if the woman wants to delay motherhood by 10 years or more, since the effect of age on egg quality may be stronger than freezing. Of course for some patients such as young female cancer patients, freezing eggs early is their only chance to have a “genetic baby”. These young women often don’t have a life partner and freezing embryos may not be an option.
