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 Center.
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 investigation.
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 men.
"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 Washi
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