Best Methods of Egg Freezing for Fertility Preservation

For many years, scientists all over the world have been experimenting with egg freezing (oocyte cryopreservation) techniques for fertility preservation. Recently, significant advances in technology have made egg freezing a clinical reality. We have been successfully freezing sperm and embryos (fertilized eggs) for many years now.

The Challenges of Freezing Eggs

Eggs have a relatively large amount of cytoplasm that tends to form ice crystals during the freezing process. This makes eggs fragile and therefore difficult to freeze. As recently as June 2008, the Practice Committee of the American Society for Reproductive Medicine stated that “oocyte cryopreservation presently should be considered an experimental technique only to be performed under investigational protocol under the auspices of an IRB [institutional review board]."

For the past two decades, egg freezing was attempted using “slow-freezing” protocols. These protocols worked very well for embryo freezing, but not for egg freezing. This was especially so because of ice-crystal formation. The introduction of vitrification (fast freezing) has been a significant advance in assisted reproductive technologies, with results similar to those achieved with freshly retrieved eggs. Vitrification can be used for freezing eggs, early stage embryos, and blastocysts (advanced stage embryos).

How Vitrification Helps

To describe things simply, with vitrification, the eggs are rapidly frozen in liquid nitrogen. As a result, ice crystal formation is successfully avoided. The process utilizes special chemicals (cryoprotectants) that prevent damage to the eggs from the liquid nitrogen. Too high a concentration of the cryoprotectants can also damage the eggs.

There are two systems available for vitrification. In open systems, the eggs are put into direct contact with liquid nitrogen during the vitrification process. In closed systems, the eggs are loaded into devices that are sealed before the vitrification process with the sole purpose of avoiding direct liquid nitrogen contact.

Developing a Successful Egg Freezing Method

At InVia Fertility Specialists, we initially proceeded with egg freezing under IRB supervision. Our first successful patient was one whose husband could not produce a sperm sample on the day of egg retrieval. We therefore cryopreserved her eggs using vitrification and, in a subsequent programmed cycle, fertilized them and transferred two embryos. The resultant twin pregnancy was uneventful.

We proceeded to electively cryopreserve eggs from a donor. These were then fertilized and transferred in a recipient (at no cost) with another pregnancy. During this time period, our embryologists gained a lot of experience with vitrification as they started routinely cryopreserving embryos using this technique. We subsequently continued to gain more experience (and success) with vitrification, and for the past six years have been offering it as a clinical service to our patients.

Good Reasons for Egg Freezing

Egg freezing was initially offered for fertility preservation in cancer patients. Other indications include fertility preservation for social reasons, egg donation programs, to avoid ovarian hyperstimulation, oocyte accumulation in low-responder patients, and surplus oocyte storage after controlled ovarian stimulation when embryo cryopreservation is not feasible (especially for religious reasons). These will be discussed in detail in a subsequent blog.

To work with a fertility team that uses state-of-the-art technology to help patients get pregnant, make an appointment at one of InVia’s four Chicago area fertility clinics.