Advances in egg freezing trigger debate

MacKenna Roberts

Progress Educational Trust

24 April 2007

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[BioNews, London]

Advances in egg freezing have leapt from the lab to the public, particularly in the US where clinics are unregulated, to offer assisted reproduction using frozen eggs despite the long-term effects being little known, according to the journal Science. A news article evaluated the reliability and significance of fertility clinics offering egg freezing services, scientifically known as oocyte cryo-preservation.

The US company Extend Fertility, based in Massachusetts, targets its egg freezing services towards young women who wish to stall their biological clock. Its advertisement campaign is controversial both in regards to the unknown risks and effectiveness of egg freezing, and concerns over its sociological impact. Extend aims to provide a lifestyle choice rather than a medical need.

But supporters argue that egg freezing has a number of advantages over embryo storage. They believe it more fairly evens the gender gap, since men can healthily reproduce throughout most of their lives, whereas women have a narrower window of fertility and their most healthy fertile years are their twenties, when many are focussing on their education and career.

Even male cancer patients have the option of freezing their sperm where as freezing eggs is more difficult and, until recently, unavailable. Women who must undergo cancer treatment could only freeze embryos, leaving no hope for single women or those without a willing partner. Egg freezing also avoids any potential bitter custody battles if a partner revokes their consent for use of the embryos at any point, as happened in the recent UK case involving Natallie Evans. Finally, embryo freezing is banned in Italy and Germany because leftover frozen embryo destruction presents ethical issues. Egg freezing side-steps this debate.

While the option of freezing eggs would be welcomed by many women, most scientists and the American Society for Reproductive Medicine (ASRM) conclude the success rates do not ethically warrant public use except experimentally for cancer patients. Egg cells are the largest human cell type containing a high level of fluid which can cause function-impairing crystallisation at low temperatures. Cold temperatures also cause the zona pellucida, the outer membrane, to become more impenetrable, making fertilisation more difficult. There is also concern that the structural disruption could cause chromosomal aberrations, potentially leading to birth defects.

The latest research on success rates shows that using 'slow frozen' eggs is about half that of fresh eggs. There is little data yet on eggs frozen by the newer vitrification technique, which involves submerging the egg in liquid nitrogen to quickly freeze it before crystals can form. Stanley Leibo, a cryobiologist at the University of New Orleans, Louisiana cited research that found vitrification reduces the average number of necessary oocytes for a successful birth from over 50 to 27-30. The long-term effects of this technique cannot yet be known but it has led to 100 births so far. Eleonora Porcu at the University of Bologna in Italy is currently compiling a comprehensive internet database to follow up children born from frozen eggs.

Reproduced with permission from BioNews, an email and online sources of news, information and comment on assisted reproduction and genetics.