Research published last month in the journal Reproductive BioMedicine Online indicates that a new freezing technique to store human eggs is safe. The study, led by Dr Ri-Cheng Chian, of McGill University, Montreal, Canada, looked at children conceived using eggs frozen by vitrification, and showed that the rate of birth defects was the same as in natural or IVF pregnancy. The study may lead the way for women to freeze their eggs to postpone motherhood.

Vitrification involves removing water from the eggs, adding an agent that acts as an 'anti-freeze', followed by very rapid cooling. This process avoids ice crystals forming which can damage the egg's structure. When this is done, 95 per cent of eggs survive the thawing process compared to 50-60 per cent of eggs frozen using previous techniques.

The new study looked at 200 children born after the technique was used, and found that only 2.5 per cent had birth defects, which is comparable to rates in natural or IVF pregnancy. The average birth weight was also no different in children conceived using vitrified eggs compared to children conceived naturally or using IVF. The freezing of eggs is not currently routinely available, as the freezing of sperm and embryos is, due to safety fears.

A woman's fertility rapidly declines after the age of 35, and there are both social and medical reasons why women may wish to freeze their eggs before this time, for later IVF treatment. Social reasons include wanting to delay motherhood to develop a career, or find the right partner. In addition, the freezing of eggs may be more acceptable to those who have ethical objections to freezing embryos. Medical reasons for freezing eggs include doing so before facing treatment that may reduce fertility, such as cancer therapy.

Currently this is the only large-scale study looking at the effects of vitrification on birth defects. Dr Allan Pacey, secretary of the British Fertility Society (BFS), said that more, similar studies are needed to verify the safety of the technique.

Reproduced from BioNews with permission, a web- and email-based source of news, information and comment on assisted reproduction and human genetics, published by Progress Educational Trust.