Flash Freezing of Eggs and Embryos

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Laboratories for assisted reproductive technology (ART) have successfully frozen sperm, embryos, and even ביצת יוני for some time now. However, success within this context is a relative term from a historical perspective. The freezing of sperm, for example, worked quite well for several decades with very few technological adjustments to the basic freezing protocols-this is because sperm do not have that much water in their composition-the more water there is the greater the likelihood that freezing damage will occur.

Embryos have a much higher water composition, and have been more difficult to freeze and thaw successfully. Still, over the past 25 years, live birth rates from thawed embryos have increased from approximately 5% to the point where, in the best programs, there is very little difference from results obtained with the transfer of non-frozen embryos in all patient categories.

Eggs have been particularly challenging because they possess unique structures that are very susceptible to freezing injury. With that said, thawed eggs too have begun to contribute significantly to live births from ART the world over. These increases in live birth rates for thawed embryos and eggs have happened through incremental refinements of what is termed “controlled rate” freezing, a process of slowly lowering the temperature of the freezing solutions that the eggs or embryos are immersed in over a several-hour period. The now-frozen specimens are then plunged into storage tanks of liquid nitrogen where they will remain-sometimes for several years-until they are needed.

Recently, a significant technological breakthrough allows extremely quick freezing of eggs and embryos. This new method, called “flash freezing” (or vitrification) appears to lower the incidence of freezing damage, and thus has the potential for higher pregnancy and live birth rates as compared to the controlled rate method. The science behind safe, non-injurious freezing methods of all types is avoidance of the development of ice crystals forming inside the specimens, be they sperm, eggs or embryos. The flash freezing method appears to minimize ice crystal formation, and is therefore an inherently safer approach.
In fact, survival upon thawing of flash frozen eggs is so high (greater than 95% usually) that it is now feasible to bank eggs removed and frozen from anonymous donors, and prospective recipients may select from a catalog containing information about the donor similar to what one finds with sperm banks. From the standpoint of patient safety and convenience, this represents a substantial change from the past-a paradigm shift, really-that brings the practice of anonymous egg donation into conformity with tissue banking laws that are applied to every other type of tissue banking.

After months of evaluative studies of the best flash freezing methods currently available, the ART Reproductive Center is well into the process of transition from controlled rate to flash freezing of eggs through blastocyst stages. Several pregnancies have been established at this point from thawed, flash frozen blastocysts, and eggs and cleavage stage embryos are now being frozen in this manner as well.

Southern California Reproductive Center was first established in 1988. In that time it has completed over 7 dozen research studies with results reported in peer-reviewed venues. It has 11 more research studies currently in process. SCRC does approximately 900 IVF cases each year. For the past three years SCRC has remained the top fertility clinic in the Los Angeles Metro area. SCRC has an affiliated surgery center as well as assisted reproduction laboratory on site. The infertility experts at SCRC also train other fertility specialists. For example, young physicians who pursue a fellowship in Reproductive Endocrinology rotate through the practice and are trained by the SCRC physicians, who are also affiliated with Cedars-Sinai Medical Center and are on the faculty of UCLA Medical School.

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