Friday, October 9, 1998 Published at 03:43 GMT 04:43 UK
Shaping up to be a dad
Fertilty definitions may be wrong
The official World Health Organisation definition of normal sperm concentration could be a poor predictor of fertility, scientists have claimed.
The WHO defines a sperm concentration above 20m per millilitre (ml) of seminal fluid as normal.
But Danish research on 430 couples planning to have their first child, reported in the Lancet medical journal, found the measure was not an accurate predictor of whether conception was possible.
Among these couples, there was an increasing likelihood of pregnancy when the man had a sperm concentration greater than 40m per ml.
However, the shape of the sperm was also found to be highly important.
Equally, men with sperm concentration below WHO's lower limit may be fertile.
The Danish research team, led by Dr Jens Peter Bonde, conclude: "The current WHO guidelines for normal semen quality should be used with caution".
Professor Ian Craft, director of the London Fertility Centre, said the WHO guidelines were only used as a "rough and ready calculator."
He said the most significant facet was the ability of sperm to move effectively in the right direction.
"A man can have a sperm count of 200m but if they all go round and round in circles, that does not help anybody at all," he said.
Professor Craft said if a man had a sperm count of less than 5m then it was highly likely that his fertility would be poor.