Men with wider variation in sperm length, particularly in the tail (flagellum), have lower concentrations of sperm that could swim well, according to a new study.
On the other hand those with more consistently made sperm seemed to have more capable ones, it found.
The finding offers fertility clinicians a potential new marker for fertility trouble that might trace back to how a patient's sperm 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 Jim Mossman, a postdoctoral scholar at Brown University and lead author of the paper.
"It suggests that in some cases, testes are working more optimally to produce high numbers of consistently manufactured sperm, and vice versa," he added.
At the University of Sheffield, where Mossman did his doctoral studies, he and his co-authors measured the heads, midpieces, and flagella of 30 sperm 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 Organization recognizes as important markers of fertility.
The result of the novel analysis 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.
But 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 percent of the cases where couples struggle to conceive," Mossman said.
The research suggests that at least in some men, measurable inconsistency in sperm length may be a sign of trouble with his process of making sperm, a process known as spermatogenesis. That trouble, akin to a manufacturing line with poor quality control, could result in a lower concentration of good swimmers.
"This could be an indirect marker of testis function," Mossman said.
Mossman acknowledged that there is nothing in the study that suggests what might cause spermatogenesis problems that would result in either inconsistent lengths or low concentrations of motile sperm.
The study was published online in the journal Human Reproduction. (ANI)