IVF clinics are using a radical male infertility treatment far too frequently despite the risk of long-term health problems to the babies conceived, according to one of the technique's pioneers.
Intracytoplasmic sperm injection involves injecting individual sperm cells directly into an unfertilised egg to improve the chances of producing a viable embryo which can then be implanted into the woman's womb.
Many of the medical problems associated with fertility treatment arise from more than one embryo being implanted into the womb, which brings a higher risk of multiple births and associated medical complications.
However, with injecting sperm directly into the egg, there are fears that it might increase the selection of genetically-defective sperm, resulting in problems such as heart disease, diabetes and obesity being passed on to future generations.
Andre Van Steirteghem, of the Brussels Free University Centre for Reproductive Medicine, was the leader of the team that developed ICSI nearly 20 years ago.
He says that although the technique has been invaluable in treating infertile couples when the man cannot produce viable sperm for conventional IVF, it should be used only when medically necessary - and that at present many clinics routinely use ICSI even when the man can still produce enough viable sperm to fertilise an egg in an IVF test tube.
Since the first IVF baby, Louise Brown, was born in Manchester in 1978, three million children worldwide have been conceived using the technology.
ICSI use has grown particularly explosively, accounting for about half of all test-tube conceptions in Britain.
Dr Van Steirteghem told the American Association for the Advancement of Science in San Diego: "I have noticed that several clinics use ICSI for everybody. I don't think it is necessary when you have methods like conventional IVF which is certainly less invasive ... When the sperm is normal, I don't see any reason why ICSI should be used.
"The health of children has to be considered the most important outcome of artificial reproductive technology treatment. It's fair to say that overall these children do well [but] there a few more problems with these children."
He added: "It doesn't mean that when you use ICSI there will be more problems, but ... monitoring is extremely important."
He is monitoring the long-term health of about 15,000 children born as a result of artificial reproductive technology such as IVF and ICSI.
His views were supported by other fertility experts concerned by the growth of ICSI.
"In the majority of IVF cases where you have functional and healthy sperm you shouldn't have to use ICSI," said Dolores Lamb of Baylor College of Medicine in Houston, Texas.