Can Crotch Length Predict Sperm Strength?03/04/11
FRIDAY, March 4 (HealthDay News) -- New research contends that
the distance between the posterior base of the scrotum and the anus
can predict the strength of a man's sperm population.
Men who have a shorter perineal length, also known as the
anogenital distance (AGD), have lower sperm counts, poorer quality
sperm, lower sperm concentrations and lower motility, the study has
Although scientists had long ago made the connection between AGD
and fertility in male rats, this is the first time it's been shown
in humans, said the researchers, whose findings are published in
the March 4 edition of the journal
Environmental Health Perspectives.
In rats, the same group of researchers established that shorter
AGD and male reproductive problems were linked to exposure in the
womb to a class of endocrine-disrupting chemicals called
phthalates, which are used to make plastics more flexible and are
found in many toys and other household products.
Phthalates disrupt normal testosterone exposure in the womb,
among other things, and have been linked to fertility problems in
women and abnormal breast growth in boys.
The new study did not examine phthalate exposure in the subjects
or their mothers, but by making a connection between shorter AGD
length (linked in male rats to exposure to phthalates) and lower
sperm counts, it does provide indirect evidence that exposure to
such chemicals may result in lower sperm counts in adult men,
according to the authors.
The researchers took two measures of AGD, along with sperm count
and concentrations, sperm shape and sperm motility, in 126 college
students in upstate New York.
The first measure was from the underside of the scrotum to the
anus and the second was from the top of the penis stem to the
The shorter measurement -- starting at the underside of the
scrotum -- was associated with sperm count, sperm concentration and
motility. The longer measurement was not.
The median AGD was about 52 millimeters so men who had an AGD
below this level were more than seven times more likely to have low
sperm concentration in the subfertile range.
Twenty-five percent of the sample "had sperm concentrations that
would have sent them to a doctor for an infertility work-up," said
study senior author Shanna H. Swan, professor and associate chair
of obstetrics and gynecology at the University of Rochester Medical
Biologically speaking, the shorter AGD reflects lower exposure
to testosterone in the womb, which can affect full development of
the genital tract in males, affecting both this size measurement
and sperm quality, she explained.
Swan and the other researchers have noted that an association
between the volunteers' lower sperm counts and phthalates exposure
in the womb is "speculative," but one that warrants further
Meanwhile, in fertility screening, AGD may prove to have
advantages over other factors that affect sperm count. Unlike other
variables that affect semen quality, such as stress, having had a
fever recently and even outside temperature, "AGD is forever," Swan
said, making any predictions more accurate.
And if the sperm count is merely low (as opposed to
non-existent), taking out a ruler and measuring may "help the
prediction of whether he's going to be successful [getting a woman
pregnant]," Swan said.
But, she stressed, "we need a lot more men to get normative
values. We need to have a couple of thousand to say what you would
expect in the general population."
One expert agreed that more research was needed to determine
AGD's possible use as a marker for fertility problems in healthy
"We don't have good ways to predict future fertility unless there are major abnormalities," said Dr. Sheela Sathyanarayana, assistant professor of pediatrics at the University of Washington and Seattle Children's Hospital, who was not involved in the study.
"This could potentially be used in the future as a marker for sperm concentration and motility," Sathyanarayana said, "[but] more research groups would need to trial this out and look to see if there are differences in AGD between men who are fertile and men who are infertile."
The U.S. National Institute of Child Health and Human
Development has more about
fertility and infertility.
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