Most fertility research has focused on the size of sperm and the size of the swimmers' heads, but a new study suggests the variability in the length of sperm also may put a wrench in successful reproduction.
Like a factory churning out products of inconsistent sizes, ejaculates with varying sperm lengths can be a problem, said James Mossman of Brown University in Rhode Island. And his study suggests a link between this variability and sperm quantity.
"There's a lot more work that must be done to characterize this relationship, to figure out why males that produce large numbers of sperm also produce better sperm," Mossman told LiveScience. This suggests those with less variation produce higher concentrations of good sperm.
Mossman and his colleagues, who detailed their results in the Oct. 28 issue of the journal Human Reproduction, say sperm-length measurements may provide insights into a man's testes function and the process through which he produces mature sperm cells.
Lots of variation
The researchers examined semen provided by 103 men who enrolled in a fertility study in 2006. They found a link between a wider variation in sperm length, particularly that of the flagellum, or the tail, and a lower concentration of sperm that could swim well. Men with a lower variation in the length of sperm components produced sperm that were more likely to be motile.