Scientists have used a new freezing technique to store eggs from 50 women who wish to put off motherhood while they pursue their careers.
The new technique, called Cryotop, could make egg storage routine and could pave the way for the first donor banks of frozen eggs.
The women donated eggs for a process called vitrification in which eggs are frozen rapidly in a drop of solution smaller than a teardrop. The eggs are then stored in liquid nitrogen at a temperature of less than -160C. The women will be able to have the eggs thawed for use in fertility treatment until the age of 50. While frozen sperm is used routinely in fertility treatment, freezing eggs for long-term storage is a lot more difficult.
Sperm are the smallest cells in the body, but eggs are the largest, and far more fragile. The Kato Ladies Clinic in Tokyo which is already banking eggs,, has already used vitrification to freeze eggs and claims that embryos created from them have a 41.9% chance of leading to a pregnancy, compared with 42% for fresh eggs.
As well as offering a new way for women to have children after cancer treatment, egg freezing could help them start families after the menopause.
The first baby born from a frozen egg was delivered in 1986 and to date, only four have been born in Britain after treatment at Midland Fertility Services near Birmingham.
There are estimated to be more than 300 babies born from frozen eggs worldwide. In Britain, a woman can freeze embryos created after her eggs have been fertilised, but this puts her in a precarious legal position, since her partner has the right to have the embryos destroyed if the relationship breaks down. A spokesman at The Kato Clinic said: "This technology opens up new horizons for medically-assisted reproduction in women, enabling them to have the option of having children at a later date by freezing eggs rather than embryos."
Gillian Lockwood, medical director of Midlands Fertility Services, said: "It is very difficult to get donor eggs in the UK because of the change in anonymity law. Women who face cancer treatment know that the therapy is probably going to save their lives, but the price they pay is it's going to ruin their fertility. Without donor eggs, their only option is egg freezing. If other centres can repeat this success, then everyone will be doing it because everyone wants the best success rates."
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