One clinic in the UK, the Assisted Reproduction and Gynaecology Centre in London, already offers women an egg bank service at a cost of £2,800 a year.

Its director says the service caters for women who want to choose when they have a baby and women whose ovaries have been damaged by cancer treatment.

The Human Fertilisation and Embryology Authority has granted the clinic a licence to freeze eggs, but not to thaw them.

This is partly because human eggs do not freeze well, and worldwide the process has only resulted in eight births, although there are more women pregnant.

Now a new approach could lead to better results according to a report in New Scientist magazine.

Process

The new system abandons the idea that eggs should be frozen in a solution similar to body fluids and instead uses a solution more similar to plant fluids.

Successfully thawed eggs can be used in fertility treatment

Eggs must be surrounded by a concentrated solution during freezing. This draws the water out of the egg cells by osmosis and reduces the risk of harmful ice crystals forming.

The process uses a saline - a salty solution - that mimics human fluids.

However, Dr James Stachecki, of the Institute for Reproductive Medicine and Science in New Jersey, has produced a study that suggests the saline may be to blame for the current low success rates.

He suspected that sodium ions from the solution were getting into the eggs and poisoning them.

His research team used a solution containing choline ions, which do not readily cross cell membranes.

Mouse eggs

Choline is an organic molecule found in many plant and animal tissues. It is a constituent of B-complex vitamins.

Dr Stachecki's team used the process on hundreds of mouse eggs. Ninety per cent of them survived the new technique and 60% of those developed into early embryos.

This compares to 50% surviving with a conventional solution and 10% of those progressing to embryonic development.

Dr Stachecki said the next stage of the research is to look at how well process works with human eggs.