'Sperm length variation may cause infertility'

The study shows that greater the inconsistency in the length of sperm, particularly in the tail (flagellum), the lower the concentration of sperm that can swim efficiently.

The finding offers doctors a potential new marker for fertility trouble that might trace back to how sperms are being made.

"Our study reveals that men who produce higher concentrations of competent swimming sperm also demonstrate less variation in the size and shape of those sperm," said lead author Jim Mossman, a postdoctoral scholar at Brown University.

"It suggests that in some cases, testes are working more optimally to produce high numbers of consistently manufactured sperm, and vice versa," Mossman said in a statement.

At the University of Sheffield, where Mossman did his doctoral studies, he and his co-authors measured the heads, mid-pieces, and flagella of 30 sperms per man, from 103 men randomly selected from a pool of about 500 who were recruited for a larger fertility study.

They also measured other characteristics of each man's semen, such as sperm concentration and motility, that the World Health Organisation (WHO) recognises as important markers of fertility.

The result yielded two overall findings: One was that men who had higher mean flagellum length, total sperm length, and flagellum-to-head length ratios had higher concentrations of motile sperm.

However, perhaps the more interesting finding was that the greater the inconsistency of length in the sperm a man manufactures, particularly with regard to the flagellum, the lower his concentration of sperm that could swim well.

"The finding could give clinicians new insight into the diagnosis and treatment of male fertility problems, which accounts for up to 50 per cent of the cases where couples struggle to conceive," Mossman said.

The study was published in the journal 'Human Reproduction'.