Cryopreservation Part 1: Oocyte Cryopreservation

Cryopreservation is a treatment for infertility that uses the latest in assistive reproductive technology to extract, freeze and store a woman’s oocytes for the future. These eggs can be thawed, fertilized in vitro, and later transferred back to her uterus as embryos or blastocysts to complete their development.

Cryopreservation has also been applied to later stages in the life of a fertilized oocyte, with advances in the technology allowing for embryo and blastocyst freezing. The freezing of sperm from the male partner, as well as his testicular tissue, can also be preserved in this way.

Egg Freezing: How it works

The retrieval of eggs for oocyte cryopreservation begins with the administration of hormone injections to stimulate the ovaries to produce and ripen multiple eggs. When these eggs become mature, ovulation is induced, and the eggs are removed using an ultrasound-guided needle. This process is done while the woman is sedated, and the needle is guided through the vagina. Once the eggs are successfully harvested, they are immediately frozen.

Eggs are frozen by one of two methods: slow-freezing or flash freezing (vitrification). Cryoprotectants are added to replace the water within the oocyte and prevent ice crystals from forming and destroying the egg cell. The slow-freeze process is a cooling process that requires the eggs to be frozen at a controlled rate. On the other hand, vitrification is much faster, but requires higher concentrations of cryoprotectants to be added.

The result of the freezing process is a solid, glass-like cell devoid of ice crystals. Studies have demonstrated that vitrification leads to a higher survival rate and better development, while the slow-freeze method has been considered safer, leaving the eggs less prone to contamination or infection.

Indications for Oocyte Cryopreservation

Egg freezing is indicated in women who are currently undergoing assistive reproductive technology treatment, but do not wish to undergo embryo freezing. Some women consider freezing embryos to be against their religious beliefs or personal ethics. This ensures that no excess embryos are created and the mother is not faced with the decision to dispose of them, simply because they are not used.

Oocyte cryopreservation is also aimed at women who have been diagnosed with cancer who have not yet initiated radiotherapy or chemotherapy, since these treatment modalities are toxic for oocytes, and few eggs that survive are actually viable. Women who simply want to postpone motherhood and preserve their future ability to have children, whether their reasons are medical, personal, or even professional in nature, can also benefit from egg freezing, and thus are allowed a chance a pregnancy when the time is right for them.