A recent study suggested that penis size might be a cause of infertility. However, experts say the research has a number of flaws.

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Experts point out that sperm are manufactured in the testicles, not the penis. Getty Images

Scientists are struggling to find out why, across the globe, men are becoming increasingly less fertile.

One meta-analysis concluded from hundreds of other studies that there is a “significant decline in sperm counts” in men over the past 40 years.

There are numerous reasons why a man and a woman may not be able to conceive, but most of the time a definitive cause can be pinned down.

But one new study suggests a new factor that may be linked to a man’s ability to conceive children: the size of his penis.

The study was conducted at the University of Utah. Dr. Austen Slade, a urologist and the study’s lead author, and his team measured the penises of 815 men between the ages of 18 and 59 who went to a men’s health clinic between 2014 and 2017.

Some were there because of concerns with their fertility, while others were there for different concerns, such as erectile dysfunction.

The study, titled “Stretched Penile Length and Infertility, a New Association,” stated that the length of a man’s penis when stretched to replicated the size while erect affected his ability to procreate.

Specifically, men with penises averaging around 12.3 centimeters — or about 4.8 inches — had a more difficult time conceiving when compared to men with penises that measured 13.4 centimeters, or more than 5.2 inches.

But does a mere 0.4 inches actually make the difference between being able to reproduce?

Maybe, but experts not associated with the research say the study has a number of flaws and could actually prompt men to take unnecessary medical action.

One major shortcoming was that the research was not peer-reviewed or published in any medical journal.

Instead, the study’s findings were presented earlier this month during a poster session at a conference for the American Society for Reproductive Medicine in Denver.

Dr. Daniel Kort, who is double board-certified in obstetrics and gynecology as well as reproductive endocrinology and infertility and works with Neway Fertility in New York City, told Healthline that given that the study has not been peer-reviewed or published in a medical journal, the scientific merit cannot be determined.

“There are a host of factors — sample size, sample distribution, outcome measures, etc. — that can be used to determine the validity of the study and thus the conclusions made,” he said.

Because the study has some of those issues, and no other study has examined the size-equals-fertility theory, so far, Kort said, “no definitive studies have shown this to be true.”

While some studies, including one in the Proceedings of the National Academy of Sciences, suggest erectile dysfunction may have a genetic link, it isn’t the same as suggesting infertility would be affected by the size of a man’s penis.

Sperm, after all, are generated in the testicles, not the penis.

Dr. Paul Turek, a board-certified urologist and men’s sexual health and fertility expert as well as founder and director of The Turek Clinics in Los Angeles, San Francisco and Silicon Valley, has similar concerns.

He said the study contains too many biases “to be even remotely believable,” including differences in age, race, and other factors that might influence the results.

It also ignores the woman’s role, as the subject’s female partners could be the reason they were childless.

“This study is a curious one, but that’s really about it,” Turek told Healthline. “Beyond the issue of scientific integrity, this makes no biological sense.”

Certainly, he said, if the penis doesn’t work properly and there is erectile dysfunction, infertility is a likely consequence.

“But, pound for pound, humans have among the largest penis among all mammals. If a centimeter of penis length mattered that much to human fertility, we would be extinct as a species,” he said. “Remember, if size were all that mattered, then dinosaurs would still be roaming the Earth.”

In order to have any kind of validity, the study would require peer-review, be able to be independently confirmed, and, of course, hold up over time.

All told, the study may do more harm than good.

“You don’t have to be in medicine or science to fathom how much psychological harm can be inflicted by unsubstantiated research on this part of the male body,” Turek said.

But besides hurting a few fragile male egos, this kind of unsubstantiated research could cause some men to chase after solutions to problems that don’t exist.

“Unsubstantiated research has the potential to increase unnecessary anxiety, which can cause a host of other problems,” Kort said. “In today’s world, such anxiety typically leads to unnecessary testing and sometimes unnecessary medical treatment.”