Scientists from the University of Michigan, US, have developed a new egg freezing technique that may improve the chances of women who want to have children following treatment for cancer.
Treatments such as chemotherapy or radiotherapy can render a woman infertile, so researchers have been looking at ways to preserve a woman's fertility. One way is to collect a number of eggs and keep them in frozen storage until the woman recovers and is healthy enough to sustain a pregnancy. However, egg freezing has long proved to be a difficult technique to perfect, as freezing and thawing egg cells tends to create ice crystals, which damage them. This is because egg cells have much higher water content than sperm, and are much larger than sperm cells, which are much easier to freeze and thaw. The first baby to be born in the US from a frozen egg was in 1997, and there have been relatively few successes since - the first 'frozen egg baby' in the UK was born in 2002. The UK's Human Fertilisation and Embryology Authority only authorised the procedure - because of safety reasons - in 2000.
Now, the US researchers have devised a technique that means an egg can be almost instantly thawed, reducing the damage done by the process. The new freezing process - known as vitrification - seems to work by allowing fewer ice crystals to form in the frozen eggs while they are returned to their usual state. The researchers say that they have tested the new process on mouse eggs, and are achieving a high 'survival rate'. They are now working on the development of a clinical technique that can be used in humans. Gary Smith, of Michigan University's Comprehensive Cancer Centre, said that 'with traditional slow-freeze techniques, just over half the eggs survive the thawing process'. He added: 'Using vitrification, we are getting a 98 per cent survival'.
The researchers have found that they have low IVF rates using vitrified mouse eggs, meaning that they need to use ICSI a variant of IVF in which a single sperm is injected directly into the egg to fertilise it. In mice, 80 per cent of thawed vitrified eggs fertilised using IVF, producing a live birth rate of about 30 per cent. Dr Allan Pacey, from the British Fertility Society, told the BBC that 'if this work bears out and the success rate is that high, it would revolutionise the way that we preserve eggs'. According to the BBC, doctors in Taiwan report that they have already achieved a pregnancy in a woman using vitrified eggs.