Scientists have found that some men will never be able to father their own genetic child, despite all the recent advances in fertility treatment.

Scientists have found that some men will never be able to father their own genetic child, despite all the recent advances in fertility treatment.

Research conducted by Monash Institute of Reproduction and Development in Australia has shown that men who have sperm with poor swimming ability frequently have a defect that prevents pregnancy even if the sperm is injected into an egg.

The injection technique -intra cytoplasmic sperm injection (ICSI) - was introduced in Britain five years ago to help men with zero or low sperm counts to father a child. Fertility specialists believed nearly all men would be able to father a child using ICSI, but the new research shows that this is not the case.

The scientists have linked poor swimming ability to a defective centriole in the neck of the sperm, which explains why many assisted fertility programmes were unsuccessful.

"If we are injecting sperm that have a defective centriole all we end up with is an embryo that can't develop," Dr Alan Trounson, deputy director and co-author of the research, told an international symposium in Rome. The centriole, found just behind the sperm head, allows the embryo to divide, forming the basis of early development.

Fertility specialists in Britain said the findings were valuable for treating certain types of patients. "This is useful knowledge for clinics and will stop patients banging their heads against a brick wall unnecessarily and trying repeated fertility treatment," said Professor Ian Craft, director of the London Fertility Centre, London. "If couples fail to fertilise the egg twice using ICSI, then it is down to donor sperm or nothing if the woman's eggs are healthy." In Britain about 6 per cent of sperm injected directly into the egg fail to fertilise it.

The research findings suggest that a greater proportion of infertility cases can be blamed on men than previously thought and shows that some couples currently spend years and thousands of pounds pursing the wrong method for their fertility problems.

The ICSI method is used by in vitro fertilisation (IVF) programmes around the world. The new research has relevance for 40 to 50 per cent of patients and could result in procedural changes to the ICSI process to make it more successful, said Dr Trounson.

Often the neck of the sperm was crushed during the process to ensure it would not swim around once it was inside the egg, but Dr Trounson said this was also damaging the centriole. "You would not want to do that. You should crush the tail instead because this little tiny engine is in the neck of the sperm," he said.

ICSI was introduced in Britain five years ago and its success rate has soared from 4 per cent to more than 21 per cent for a live pregnancy. It is one of the most popular forms of fertility treatment and, so far, more than 3,000 ICSI babies have been born out of the 36,000 made possible by assisted conception techniques available in Britain.