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Egg freezing has long been the holy grail of the fertility world. Although sperm and embryos (fertilized eggs) have been successfully frozen for the purposes of extended fertility preservation for decades, the freezing of unfertilized eggs (oocytes) has only recently been successful.


In the past, difficulty with egg freezing was due to an egg’s tendency to develop ice crystals during the freezing process (which compromises the integrity of the egg), as well as hardening of the egg’s outer membrane, making fertilization difficult. Two recent breakthroughs have allowed scientists to overcome these problems.

The first is the development of a new culture media system that protects the egg from damage during the freezing/thawing process. The media system dehydrates the egg during freezing and rehydrates the egg during thawing, thereby minimizing the formation of ice crystals. The second breakthrough is a fertilization technique known as ICSI (Intra-Cytoplasmic Sperm Injection). With ICSI, the embryologist injects the egg with a single sperm in order to fertilize it.

By applying these new advances in cryopreservation, scientists have realized a sharp increase in post-thaw survival rates (as high as 90%)1 and fertilization rates (as high as 80%)2. These improvements have led to pregnancy success rates from frozen eggs of up to 35% per embryo transfer,3 and have facilitated a dramatic increase in the number of babies born from frozen eggs to over 1,000 worldwide.4

Experience & Innovation

Extend Fertility has identified leading centers that have “superior” success rates with frozen eggs. All Extend Fertility partner centers are carefully trained and monitored by recognized experts in the field of egg freezing.

Extend Fertility is committed to advancing the science of egg freezing. Working together to maximize success, Extend Fertility’s partner centers have made several proprietary improvements to the existing published protocols, often yielding better results than appear in the current literature. Our centers are also currently involved in ongoing research studies to improve the published data and significantly increase the number of babies born from previously frozen eggs. Read the initial study results

  1. Data from an unpublished study conducted in the RMA of New York laboratory.
  2. As reported in an abstract entitled “Comparison Between Two Different Human Oocyte Cryopreservation Protocols on Survival, Fertilization and Embryo Development” presented at the Pacific Coast Reproductive Society Meeting by Huntington Reproductive Center in April, 2005.
  3. An Extended Fertility survey of the 11 peer-reviewed published reports on egg freezing using ICSI through 2004 that provide the relevant data yields an average pregnancy success rate per embryo transfer of 35.2%.
  4. Reproductive BioMedicine Online 2009 [e-pub ahead of print on 8 April 2009]

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