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Egg Freezing and Vitrification

How Does Egg Freezing and Vitrification Work


Updated October 21, 2012

Egg freezing and vitrification have been widely publicized. The use of vitrification technology to freeze eggs offers a new option for cancer patients looking to preserve their fertility, and magazine articles have proclaimed that egg freezing with vitrification is "woman's emancipation" from age-related infertility.

But what is egg freezing? What is vitrification? Can it really bypass age related infertility?

What Is Egg Freezing?

Egg freezing, also known as oocyte freezing, has been around for years, but generally has been less than successful and only available as an experimental technique of fertility preservation.

While embryo freezing -- which is the freezing of a fertilized egg -- works well, freezing unfertilized eggs is trickier. If a young or single cancer patient wants to preserve her fertility, freezing fertilized embryos would only be an option if donor sperm is used to fertilize the eggs.

That's why researchers have been experimenting with freezing unfertilized eggs, to provide options to young or single cancer patients. Some female cancer patients risk losing their fertility because certain kinds of chemotherapy treatments, and certain types of radiation treatments, can bring on premature menopause, rendering them sterile. Not all cancer treatments lead to infertility, but many do.

There is also interest in the subject as a method of extending fertility in healthy women, possibly taking away age-related barriers to childbearing. Eggs frozen from your younger years, theoretically, could be used years later during IVF treatment, if age-related infertility strikes before you're ready to have kids. (Read more about age and fertility.)

What Is Oocyte Vitrification?

Until recently, the only method for freezing oocytes (or unfertilized eggs) was a slow-freezing method. Unlike sperm, which has been successfully frozen and used for years, eggs contain a great deal of water, which makes freezing more difficult. When the eggs are frozen, ice crystals can form within the egg. These ice crystals can destroy the cell's structure.

To help minimize the amount of ice crystals, scientists would remove some of the water as the egg was slowly frozen. But it's impossible to remove all the water, and they couldn't prevent the formation of some ice crystals. The fertilization and pregnancy rates for these slow-frozen eggs, once thawed, is low.

Vitrification is a specialized freezing technique, which freezes the egg so quickly, ice crystals don't have time to form.

How Does Vitrification of Eggs Work?

Vitrification of eggs involves using high concentrations of an anti-freeze substance. Because anti-freeze is potentially toxic to the egg, the technique requires special care.

The oocyte is first placed in a bath with a lower concentration anti-freeze, along with some sucrose, or sugar, to help draw some of the water out of the egg. Then, the egg is placed in high-concentrated bath of anti-freeze for less than one minute, while being instantaneously frozen.

When it's time to thaw the egg, the oocyte must be warmed quickly and removed from the anti-freeze solution right away. Once thawed, the egg can be fertilized using ICSI, an assisted reproductive technology that injects one sperm directly into an egg.

When Is Egg Freezing With Vitrification Used?

Embryo freezing is still the preferred technique for fertility preservative, but this new technique is being used for young or single cancer patients, who don't want to use a sperm donor.

In research labs, vitrification is also being tried out for ovarian tissue preservation. Ovarian tissue preservation, also known as ovarian cryopreservation, is another experimental technique being used to preserve fertility in female cancer patients. It involves removing one ovary or part of an ovary, freezing it, and later, implanting the ovary in the woman's body after cancer treatment is completed.

Vitrification of eggs is also being used to help preserve fertility in young women who want to delay motherhood, but don't want to worry about age-related infertility. As women get older, the risk that they'll have trouble conceiving rises. Some fertility clinics are marketing vitrification to women who want to wait for motherhood, or don't have partners yet and are worried about their ticking biological clocks.

Controversy Regarding Egg Freezing Services

Marketing and offering vitrification to women looking to avoid age-relate fertility problems is controversial. The American Society of Reproductive Medicine is against the idea, saying that the technique is too new, and does not have enough research to prove it'll be successful enough to be worth it.

Only a few hundred pregnancies have come from vitrified egg freezing, and none of those included eggs frozen for years at a time. The majority of the research focuses on eggs frozen for a matter of hours or months.

From the other side, fertility doctors who are marketing vitrification claim that the latest research shows that the technique is successful, and it's time to release the new technology to those that want to try it.


ASRM Urges Caution, Strong Counseling for Women Seeking Egg Freezing. Press Release. Highlights from the 63rd Annual Meeting of the American Society of Reproductive Medicine. Accessed September 23, 2008.

Cobo A, Domingo J, Alamá P, Pérez S, Remohí J, Pellicer A, and Almenar-Cubells D. "Oocyte vitrification: A new approach for fertility preservation in cancer patients." Journal of Clinical Oncology. 26: 2008 (May 20 suppl; abstr 20727).

Cobo A, Kuwayama M, Pérez S, Ruiz A, Pellicer A, and Remohí J. "Comparison of concomitant outcome achieved with fresh and cryopreserved donor oocytes vitrified by the Cryotop method." Fertility and Sterility. 2008 Jun; 89(6):1657-64. Epub 2007 Sep 24.

Egg, Ovarian Tissue, Embryo, and Sperm Freezing. The Infertility Center of Saint Louis. Accessed September 23, 2008. http://www.infertile.com/infertility-treatments/freeze.htm#vitrification

Lucena E, Bernal DP, Lucena C, Rojas A, Moran A, and Lucena A. "Successful ongoing pregnancies after vitrification of oocytes." Fertility and Sterility. 2006 Jan; 85(1):108-11.

The Ethics Committee of the American Society for Reproductive Medicine. "Fertility preservation and reproduction in cancer patients." Fertility and Sterility. 2005 June. 83(6):1622-1628. http://asrm.org/uploadedFiles/ASRM_Content/News_and_Publications/Ethics_Committee_Reports_and_Statements/FertilityPreservation.pdf

  1. About.com
  2. Health
  3. Fertility
  4. Fertility Treatments: Clomid, Fertility Drugs, IUI, and IVF
  5. The Science Behind Vitrification and Egg Freezing

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