Family life is particularly precious to Eloise and Gary Jacobs. Six years ago they discovered that an operation had left Gary with an extremely low sperm count which made it impossible for him to father a child.

The BBC's Susan Watts reports

Eloise says: "As soon as someone tells you can't have children, it closes a door on your future."

"Then to start to have to consider that the child the wife desperately wants may not be genetically mine became something I really didn't want to deal with," says Gary.

"I felt that way because if in the future my child ever had a problem with me for whatever reason, I never wanted to hear, 'well you're not my real daddy anyway'."

Eloise and Gary now have three children - twins aged two-and-a-half, and a four year old daughter. All were conceived using a method of assisted reproduction called intracytoplasmic sperm injection - or ICSI.

The process is ideal for couples in which the male has poor sperm but who want any offspring to be genetically related to them.

Using the technique a single sperm is injected directly into an egg to fertilise it. .

ICSI circumvents nature, because it uses sperm that would not normally "make it" in the competitive journey inside a woman's body in which sperm battle it out to reach and fertilise an egg.

'Wonderful technology'

Mr Paul Serhal, of the assisted conception unit at University College Hospital London, says the technique has made a huge difference.

Mr Paul Serhal: "Breakthrough"

"Up until recently there was no credible treatment for male infertility," he says. "Now we have this wonderful technology whereby we can inject the sperm right into the egg."

The Jacobs were among the first people in the UK to benefit from this technique - but hundreds of other couples have followed their lead.

The technique was pioneered in the early 1990s, and by 1995 some 50,000 ICSI cycles were already undertaken around the world each year.

ICSI is now well on the way to becoming the standard method of treatment of male infertility through IVF - and in some British clinics up to 45% of their IVF procedures are ICSI.

An estimated 20,000 children have been born using this method.

Professor Lord Robert Winston disagrees there is a significant risk

But now, nearly nine years after the treatment was pioneered, concerns are being expressed about the potential problems faced by ICSI children.

The problem is that six per cent of men with infertility problems will also have a genetic mutation that they will pass on to all male offspring. This will render these male children infertile themselves.

Screening

On top of this, eight per cent of infertile men have chromosomal abnormalities which could lead to any of a range of genetic diseases, from Down's syndrome to cystic fibrosis, in their children.

Infertile men are 10 times more likely than the average man to carry these genetic abnormalities. However, genetic testing for potential parents using ICSI is not routine.

Mr Serhal said: "We had a patient recently who came for a second opinion. She's had four treatment cycle with IVF and ICSI and been pregnant four times. Unfortunately she has had four miscarriages.

Infertile couples can be desperate for children

"When we checked the husband's chromosomes it turned out that he did have chromosomal abnormality.

"Such cases should not happen. Clinics should screen all patients before they're subjected to treatment."

The problem is that there has been very little research into the difficulties ICSI children might face.

Two studies this year, one in Australia and one in Belgium, painted a confusing picture. Both indicated decreased mental development of children conceived by ICSI - particularly among ICSI boys.

Trials

But further research is desperately needed to pin down the exact size of the effect.

Newsnight also understands that the Food and Drug Administration in the US is now so concerned about the technique it is to initiate clinical trials at leading fertility centres there, even though ICSI is now practically the treatment of choice for male infertility at many clinics.

The largest study ever carried out on ICSI children is taking place at London's Royal Free Hospital - testing their cognitive development at one year old.

Dr Alistair Sutcliffe: "Monitoring"

Dr Alastair Sutcliffe says there is a lack of hard data, and that the work he's doing should ideally have been carried out sooner.

He says: "It had to be brought in quickly because of those couples who couldn't conceive in any other manner."

But he said there should have been put in place a system to monitor the progress of ICSI children after birth.

The desire for a baby that carries the parents own genes can be overwhelming, and fertility clinics have found it hard to resist the enormous pressure from couples desperate for a child of their own.