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Dr. Jaime Mendiola and colleagues the University of Rochester Medical Center in New York have developed a simple screening tool for male fertility

But The Important Measurement Probably Isn't What You Think

Dr. Jaime Mendiola and colleagues the University of Rochester Medical Center in New York have developed a simple screening tool for male fertility. And they based their measurement of male fertility in humans on what scientists know about rats.

Scientists have known for a long time that male baby rats that are exposed to the right balance of estrogen and testosterone in the womb have the greatest fertility. There are, of course, any number of hormone measurements that can predict male fertility, but a very simple way to estimate fertility in male rats is to measure the distance from the base of the scrotum (in common language, the ball sac) to the anus. The longer the anogenital distance, the higher the male fertility in rats. The University of Rochester researchers set out to see if the same principle applied in people.

Recruiting 126 male volunteers in the Rochester area, the scientists measured both the distance from the anus to the scrotum and the distance from the anus to the "insertion" of the penis in the abdomen. They then took semen samples and measured total sperm count, total motile (or moving) sperm count,  sperm concentration, and sperm morphology, looking for "non-swimmers." They then compared all of these measurements of sperm count and quality against the measurements of anus-to-scrotum distance and anus-to-penis distance.

Wider Is Better When It Comes to Sperm Count and Quality

The University of Rochester researchers found that anus to scrotum distance predicted every measure of sperm quantity and quality, while anus to penis distance did not have any relationship to any measure of fertility. Men who had anus to scrotum widths less than average were 7 times as likely to be infertile as men who had anus to scrotum widths greater than average. Men with wider anogenital territory had higher total sperm counts, more sperm per cubic centimeter of semen, more motile sperm, and fewer defective sperm. Men in the 75th percentile of anus to scrotum distance had sperm counts roughly 50 per cent greater than men in the 25th percentile.

The scientists believe that these characteristics are set before birth. Men who are exposed to more estrogen in the womb, especially men who were exposed to a chemical called diethyl silbestrol, or DES, have less development of the testes and penis and less fertility later in life. This measurement is an easy way to identify such men in the clinic.

However, the University of Rochester researchers are hardly the first to notice a relationship between the anogenital region and male fertility. Traditional Chinese acupuncture and traditional Japanese acupressure both teach that stimulating this area manually increases both fertility and erectile strength. Traditional Chinese and Japanese medicine does not have a theory explaining estrogen exposure in the womb, but practice of this kind of massage is a standard recommendation for couples seeking to conceive and for men experiencing erectile dysfunction or premature ejaculation.

  • Mendiola J, Stahlhut RW, Jørgensen N, Liu F, Swan SH. Shorter Anogenital Distance Predicts Poorer Semen Quality in Young Men in Rochester, New York. Environ Health Perspect. 2011 Mar 1. [Epub ahead of print]