Nov. 7, 2001 -- When it comes to human coupling, good looks rule. All else being equal, attractive people often have a big advantage in finding mates. Now it seems that for men, appearance may be critical at a cellular level as well. New research suggests that having good-looking sperm is the most important determinant of male fertility.
In the most comprehensive study of its kind, researchers from a National Institutes of Health study group reported that a man's ability to procreate is greatly influenced by the shape and appearance of his sperm. Writing in the Nov. 8 issue of The New England Journal of Medicine, the group recommended that sperm appearance, known as morphology, be used to assess male fertility along with sperm count and movement.
The National Cooperative Reproductive Medicine Network also found current standards for evaluating semen to be misleading. They proposed a different measure, which would create a "gray area" of male fertility. Men now considered infertile under the World Health Organization (WHO) guidelines adopted half a century ago might be considered borderline under the proposed criteria.
Lead researcher David S. Guzick, MD, PhD, of the University of Rochester Medical Center, tells WebMD the study findings demonstrate what many doctors have long suspected: Male infertility is not as clear-cut as current laboratory guidelines suggest.
"The current standards treat sperm quality like a light switch. If it falls above a certain value it is normal, and if it is below that value it is abnormal -- like turning a light off and on," Guzick says. "But we found that there is a big overlap and that male infertility is really a biological continuum. Focusing infertility efforts on the man who is in this gray area may be a waste of time and money."
About one out of six couples experience problems conceiving, and in 30% to 40% of cases the male is considered to be infertile. In this study, Guzick and colleagues analyzed semen samples from both fertile and infertile couples in which tests on the female showed no abnormalities.
Current WHO guidelines classify sperm as normal if a sample contains 20 million sperm per milliliter and at least 50% of the sperm are moving. If there are fewer sperm per sample or less than half are moving, the sperm are considered abnormal.
Under the newly proposed standards, sperm would be considered normal if a sample has a concentration of 48 million sperm per milliliter, more than 63% of the sperm are moving, and more than 12% have a classic oval appearance.
The gray zone would be defined as sperm concentrations between 13.5 million and 48 million sperm per milliliter, with between 32% and 63% of sperm moving and 9% to 12% of sperm having a uniform appearance. Men with sperm values below these would be considered infertile.
"These recommendations provide a more reliable means for estimating the likelihood of a man's fertility," said Duane Alexander, MD, director of the National Institute of Child Health and Human Development. "This will prove a valuable tool for specialists treating couples with unexplained infertility."
While sperm appearance may be highly significant, assessing morphology is time intensive and requires highly trained technicians. Guzick says few laboratories are currently set up to routinely measure the morphologic features of sperm.
"Semen analysis is routinely done using a computer, but you couldn't do that in this case," he says. "So it would probably be very costly to implement. But our findings suggest that assessing morphology is the best discriminator of fertility and infertility."