egg-freezing

The science of egg freezing

egg freezing science and history

Oocyte cryopreservation, also known as egg freezing, is now a reality in the specialty of reproductive endocrinology and infertility. It has opened many new and exciting avenues of treatment options for assisting the infertile population but also has new applications for women wishing to preserve their fertility for medical indications or personal reasons.

A Brief History of Egg Freezing

To best understand the current status of egg freezing it is helpful to view the historical evolution of In-Vitro Fertilization (IVF) which in 1978 resulted in the birth of Louise Brown, the first human conceived in the laboratory. In IVF, eggs are harvested from the woman’s ovaries after priming their growth with specific hormone medications. The harvested eggs are inseminated and become embryos in the lab within three days. A limited number of embryos are then transferred to the uterus, potentially leaving a surplus, which is usually frozen for a future transfer if the first try is unsuccessful. However, if pregnancy occurs during the first attempt, embryo disposition can be problematic due to conflicting opinions about their status in society. Clearly, a potential solution to this dilemma is to inseminate a limited number of eggs after harvest and freeze the unfertilized eggs until needed in the future. Unlike an embryo, the egg is a single unfertilized cell, which in some groups simpler to discard when no longer needed.

Sperm Freezing and Embryo Freezing

It is interesting to consider that human sperm (spermatozoa), which are 1000 times smaller than a human egg, have been successfully frozen since 1955. Due to their ultra microscopic size, they contain a relatively tiny amount of water, making them resistant to the effects of freezing. A few years after the first successful In-Vitro Fertilization (IVF) birth in 1978, great interest led to the first successful report of human embryo freezing, resulting in a live birth in 1983. Therefore, by the early 1980’s both human sperm and embryo cryopreservation became established in the majority of IVF centers.

The advantages of freezing unfertilized eggs at once became apparent and researchers turned their attention to this endeavor. However, the techniques used to freeze embryos did not readily lend themselves to unfertilized egg freezing by nature of the egg’s physiology and structure. In the mid 1980’s preliminary reports of low success with egg freezing and thawing were disappointing and this area of research remained dormant. Research efforts were instead redirected to improving embryo freezing thereby leaving the dilemma of frozen surplus embryos unresolved.

The Physiology of Human Egg Freezing and Thawing

The Egg Freezing Process

Progress in egg freezing remained stagnant because early trials of egg freezing used suboptimal freeze/thaw protocols, which did not address the structural differences between oocytes and embryos. The intent of most freezing protocols is to achieve simultaneous exchange of intracellular water with protective solutions in a limited amount of time, under special lab conditions, without causing injury to the target tissue. Since the human egg is the largest cell in the body and is composed mostly of water, the formation of ice during freezing can disrupt the egg’s internal microscopic contents and its outer membrane. Therefore cryoprotectants, which act as “antifreeze solution" are used to dehydrate the water and replace it with the protective solution to reduce internal ice formation.
It is a known fact that osmosis causes an exchange of the egg’s inner cell water with cryoprotectant fluids by diffusion across the egg membrane. To facilitate the transference of the fluids, a delicate balance of the solution’s concentration, the time exposure to the solutions and the temperature of the culture system are needed to achieve optimal levels of water replacement. However, the dilemma is that these cryoprotectants tend to be cytotoxic and as such they may damage the egg if exposure is too long at “high” temperatures (4 to 37 degrees Celcius). So the science of egg freezing (cryobiology) is all about compromise: how to remove water as quickly as possible, without damaging the egg.

The Egg Thawing Process

The science team at Frozen Egg Bank, noticed that equally important to a successful freezing program is the development of a robust thaw protocol that insures the survival of the egg when ready to be fertilized. Cell death can occur if conditions are not optimal during the reanimation sequence. It is crucial that patients planning to freeze their own eggs or plan to use frozen donor eggs verify that their medical provider is familiar with the critical steps involved in the thaw procedure.
In addition to egg thaw survival, there is also the obstacle to sperm penetration into the egg due to hardening of the outer membrane preventing conventional fusion and entry through the egg’s surface. To overcome this obstacle, our scientists use the technique of Intracytoplasmic Sperm Injection (ICSI), to mechanically inject a single sperm cell into the egg, (See Video).

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The Current Status of Egg Freezing at Frozen Egg Bank, Inc.

Previously, the low success described in early published medical articles seemed to perpetuate the false notion that egg freezing would never become a reality. The concept and the demand for egg freezing existed but obviously a new direction of thinking was needed to identify the specific requirements for the freezing and thawing of eggs versus embryos.

Fortunately, the medical and scientific team at the Frozen Egg Bank believed differently about the future of cryopreservation. Building on our high success rate with embryo freezing, our focus turned to the systematic analysis of the anatomy and the fluid composition of a human oocyte and its special requirements needed to survive the rigors of very low freezing temperature and still maintain its integrity.


Our medical and scientific team has conducted very promising research leading to a patent pending method of egg freezing that has made it more readily available and progressively successful. West Coast Fertility Centers, in association with Frozen Egg Bank, has reported a much higher frozen egg pregnancy rate between 2005-2008, compared to other published data. It is probable that some reporting clinics and IVF programs may have used suboptimal protocols that yield very low success rates and dissapointing pregnancy rates. By making continuous modification in our techniques, Frozen Egg Bank’s team of scientists has perfected the LANDA Technology for egg freezing and thawing (cryopreservation) resulting in the birth of 70 healthy babies. This number is among the highest in the nation from a single fertility clinic and also includes high numbers of ongoing pregnancies from the use of frozen eggs. At Frozen Egg Bank and its research partner, West Coast Fertility Centers, we strive to help our patients achieve their hopes and dreams of one day completing their family.

Frozen Egg Bank, Inc. Offers Frozen Donor Eggs Preserved with Both Freezing Techniques

Egg Freezing Slow Freeze Process

Egg Freezing Vitrification Process

Is Egg Freezing Right for You?

In summary, the last few years have seen a significant resurgence of interest in the potential benefits of human egg freezing as shown below.

  • Provision of egg cryostorage for women wishing to preserve their reproductive choices
  • Convenient cryopreservation of eggs for women about to undergo therapy which may be harmful to reproductive tissue (e.g. prior to cancer treatment by radiation or chemotherapy)
  • Due to growing ethical concerns regarding the fate of surplus embryos following in-vitro fertilization (IVF), oocyte cryopreservation is a viable option. The survival rate of frozen eggs is surprisingly similar to that of frozen embryos but may prove to be a better alternative for the patient.
  • The patient can chose to inseminate only a few oocytes creating a few embryos for transfer, and freeze the remaining unfertilized eggs for future use. The option of freezing an oocyte instead of an embryo may be more acceptable to some patients with ethical concerns.
  • At Frozen Egg Bank, the formation of a donor “egg bank” is now available to facilitate and lessen the cost of obtaining frozen donor oocytes for women who need donor eggs to have the baby of their dreams.

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