Cryopreservation of embryos has become a routine part of IVF cycles that produce extra embryos. Cryopreservation of eggs is a new technology that holds great promise for future fertility preservation.
Eggs are more difficult to freeze than embryos because they have a delicate membrane (zona pellucida) that can be damaged by the freezing process. Water molecules must be removed to prevent ice formation rupture of this membrane.
Egg freezing requires a technology called vitrification that freezes the eggs fast enough that ice crystals do not often form. The ability to successfully freeze and thaw eggs has many exciting clinical applications. Cancer chemo or radiation therapy will destroy viable eggs and women scheduled to undergo these procedures could preserve their eggs prior to treatment. The eggs could be thawed and used in future IVF cycles.
Many women also want to delay pregnancy until their careers are established or other personal goals are met. Egg quality declines as women age thus greatly reducing the chances of future pregnancy. These women could freeze their eggs while younger thus preserving their fertility. The incidence of abnormal genetic processes and miscarriage also increases with “egg age”.
It might also be possible to create donor egg banks that would help many women with declining ovarian function. While embryos can be frozen, the number of eggs that could be frozen is much greater. Eggs from one egg donor could be used by many couples.
While all of the technical issues required to successfully freeze and thaw eggs have not yet been resolved, the future holds great promise. Currently, many women have frozen their eggs and pregnancies have resulted from thawed eggs.