It's not just the number of sperm that matters – they need to be the same LENGTH, too
Experts compared semen samples from more than 100 men who had fertility problems
They found that consistent tail-length trumped average length when it came to strong-swimming sperm
17:02 GMT, 17 December 2012
Men have a better chance of having children if they have semen teeming with strong-swimmers.
Now fertility experts say they have found a good indicator of what makes sperm good movers in the first place.
A study from Brown University in Rhode Island, found sperm that had tails of a similar length were better able to travel than those with tails of varying lengths.
Successful sperm: Consistency of sperm tails was found to be more important than average length
The team led by James Mossmon were surprised to find that tail
consistency trumped average length.
The findings add to our understanding of why some couples struggle to have children.
Around one in six couples may have difficulty conceiving in the UK – which is around 3.5million people. Couples are recommended to visit their GP if they have not conceived after one year of trying, or sooner if the woman is aged over 35.
For the study, researchers from Brown University in Rhode Island examined the semen of 103 men attending an infertility clinic at Sheffield Teaching Hospital NHS Foundation Trust.
They found that the wider the variation of sperm length in samples,
the lower the concentration of motile sperm. The variation in tail length was found to be the most crucial factor.
Writing in the journal Human Reproduction, the scientists said: 'Sperm length measurements may provide a useful insight into testis function and the efficiency of spermatogenesis (sperm cell development).'
Only one per cent of the 300million sperm released by a man during sex reach their partner's uterus
It is another piece in the jigsaw that explains why only one per cent of
the 300million sperm released by a man during sex manages to reach their
partner's uterus, while just a few dozen reach the egg.
Research published earlier this year from the University of Warwick and University of
Birmingham revealed sperm has an appalling sense of direction.
The team injected sperm cells into hair-thin microchannels
to study how they behaved in confined spaces.
They found sperm avoid the 'middle lane' of the female
reproductive tract and instead crawl along the channel walls. They also struggle to turn sharp corners and crash into the
walls and each other in a scene reminiscent of a demolition derby.
Only one sperm enters a woman's ovum as afterwards
the cell membrane of the egg hardens and the remaining sperm die.