By Jack Flanagan

Women should freeze their eggs at the age of 25 if they want to prolong their chances of having children, experts have warned.

Dr Hana Visnova, a celebrated specialist in reproductive health, says women who choose to put motherhood on ice in their 30s are being sold 'false insurance'.

Each year thousands of UK women undergo elective freezing for 'social reasons' in the hope of stopping their biological clocks and delaying having children until later life.

But Dr Visnova warns these women might face fresh disappointment when they come to use them because they did not freeze their eggs while they were in their 20s.

Dr Visnova, medical director of IVF Cube in Prague, Czech Republic, said: 'The quality and quantity of a woman's eggs diminishes with age. As such, egg freezing has become much more common. But it is not the miracle cure that many women think.

'The human egg is the largest cell in the body and once it is frozen it becomes difficult to thaw, with eggs less likely to survive the defrosting process compared to embryos.'

During egg freezing the patient undergoes the first part of the IVF process, which includes the hormonal stimulation of the ovaries. The eggs are then retrieved and cryopreserved in tanks with liquid nitrogen.

When they are ready to be used, they are thawed and those that survive are injected with sperm to fertilise the egg.

In the UK in 2013 just 14 per cent of attempts with frozen eggs resulted in births. This rate was far lower for women over the age of 38, according to the Human Fertilisation and Embryology Authority (HFEA).

Research by IVF Cube showed their pregnancy rate with fresh eggs was 68.05 per cent, while with frozen eggs it was just 42.86 per cent.

Dr Visnova points to research which suggests that to achieve a 90 per cent probability of having a pregnancy from frozen eggs, around 35 eggs will need to be retrieved.

In each cycle around six to eight eggs are retrieved, on average.

Dr Visnova said: 'If someone wants to freeze their eggs between the ages of 25 and 30 they can get around 15 to 20 eggs from one stimulation.

'At such a young age, she can maybe repeat the stimulation twice and get a sufficient number of eggs for the future.

'But if you get close to 40, then we can expect her to have six, maybe eight eggs. Sometimes only four.

'And if the estimated amount to achieve a pregnancy in the future is around 30 to 35 eggs then this can mean she needs to repeat the stimulation six or seven times, and then you're looking at huge costs and all the associated risks.

'If a woman has been through stimulation in her 30s and not retrieved enough eggs, then she will face new disappointment in her 40s when she discovers that from 10 frozen eggs, maybe only five have survived the thawing process.'

In 2001 just 29 women chose to freeze their eggs for later use. In 2014, 816 opted to freeze their eggs - a 25 per cent increase from the year before.

More recent figures are not available but it is expected that in the last four years this number will have again risen significantly.

'Women should be freezing from the ages of 25 to 28'

Dr Visnova said: 'Vitrification is still a relatively new method, so we're only now starting to see the outcomes, and they usually only relate to the pregnancy rates from frozen eggs from young donors.

'We still don't have enough evidence of the outcomes for frozen eggs from older women, but what we have seen from them are quite disappointing.'

She advises women should be freezing their eggs a decade earlier than previously thought.

Dr Visnova said: 'Women should be freezing from the ages of 25 to 28, 10 years younger than the group of women who are now attending clinics for egg freezing.

'It is difficult, because at 25 many women don't consider their future fertility, and are too young to think about what might happen 10 years down the line.

'There's also the financial implication, which at such a young age isn't really a priority for many.'

In the UK the average cost of retrieving and freezing eggs ranges from £2,500 to £5,000. Storage costs can then vary from between £150 and £400 a year.

Eggs can be stored for up to 10 years, although some women may be eligible to store their eggs for up to 55 years.

In the Czech Republic egg freezing procedures, including egg retrieval, cost around £1,750.

Dr Visnova added: 'After being made fully aware of the pros and cons some women in their late 30s and early 40s do still want to do this.

'They want to increase their chances, even if it's just by a very small amount, wherever possible.

'This is fully understandable. But those in the fertility industry must protect women against false hopes and be realistic about the expected outcomes from frozen eggs.'