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The sperm of all 18-year-olds should be frozen for use in later life because of the risks attached with being an older father, a UK bioethicist has argued.

Sperm becomes more prone to errors with age, increasing the risk of autism, schizophrenia and other disorders.

Dr Kevin Smith, from Abertay University in Dundee, says sperm-banking on the NHS should "become the norm".

The British Fertility Society said such a move would "provide a very artificial approach to procreation".

It called for a greater focus in the UK on supporting young couples to have work and have children.

Men are having children later - the average age of fatherhood in England and Wales has increased from 31 in the early 1990s to 33 now.

But while it remains possible to have children well into old age, there are consequences.

Making his case in the Journal of Medical Ethics, Dr Smith said even small increases in the risk of disease could have a big effect when scaled up across a whole nation.

Image caption Dr Kevin Smith says sperm banks should "become the norm"

He told the BBC News website: "I think on a society-wide basis, we do need to worry about it - it is a very real and pronounced effect.

"It's time we took seriously the issue of paternal age and its effect on the next generation of children."

His solution is sperm banking for everyone on the NHS so that in older age men can turn to the sperm from their younger selves.

He said there was no fixed age when someone could become an "older dad" but that people in their 40s might want to return the sperm bank freezer.

He said sperm should be banked ideally around the age of 18.

It costs £150-200 per year to keep sperm privately, although an NHS equivalent should be cheaper to run.

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Allan Pacey, a professor of andrology at the University of Sheffield, said: "This is one of the most ridiculous suggestions I have heard in a long time."

He said the risks from fathering children later in life were "really quite small".

"We know that the sperm from the majority of men won't freeze very well, which is one of the reasons why sperm donors are in short supply," he added.

"Therefore, men who froze their sperm at 18, and returned to use it later in life, would essentially be asking their wives to undergo one or more IVF procedures in order to start a family."

'False security'

Professor Adam Balen, chairman of the British Fertility Society, disagreed with the need for a universal sperm bank.

He said: "Not only does it provide a very artificial approach to procreation, but also a false sense of security as the technology does not guarantee a baby."

He warned that frozen sperm were less fertile than fresh ones and couples would be likely to have to depend on IVF.

Prof Balen argued: "I don't think we should be advising all women and men to freeze eggs and sperm for an uncertain future, but support young couples to have work and have children - that may require a societal shift in philosophy."

He said other countries, particularly in Scandinavia, were better than the UK at providing childcare and maternity and paternity leave.

Sheena Lewis, the chair of the British Andrology Society, said: "Men should think about their families much earlier in their lives.

"We need to get the message across that it's really a much better idea for men as well as women to have their children in their 20s and 30s."