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February 25, 2022

Does penis size affect fertility?

In 2021, a study published in Translational Andrology and Urology found a correlation between infertility and shorter “stretched penile length.” But is it really harder to get someone pregnant if you have a smaller penis? The short answer is no. The study needs more context — so let's delve into the connection between penis size and fertility a little further.

Key takeaways

  • Penis size and fertility may be correlated, but the relationship is indirect— both are influenced by testosterone levels, among other factors. People with penises of all lengths, widths, and shapes have children naturally.
  • Testicular size is also unlikely to affect fertility, except in cases of testicular atrophy (shrinkage).

The research on penis size and fertility is mixed

The authors of the study highlighted above explain that the results do not suggest that men with smaller penises have reduced fertility, or that men with infertility have reduced penile lengths. The study notes a weak association between adult testosterone levels and penile size, and a small difference of 1.1 centimeters between the average penile length of fertile men and infertile men.

There are many limitations to the research. The group of men studied was small, not randomized, and conducted retrospectively. It doesn’t account for differing populations, or race and ethnicity. And the authors theorized that the lower fertility and the lower penile length were actually both symptoms of the primary issue, which was lower testosterone.

There is currently no further research to link penis size and fertility. And people with penises of all lengths, widths, and shapes have children naturally.

What affects penis size?

Penis size is believed to be mainly genetic. It’s not just inherited from your father; it’s a unique combination of genes received from both parents. (Male siblings can have penises of different sizes, since they inherit a different combination of chromosomes.) Interestingly, while genes from your father determine your biological sex and whether or not you’ll develop a penis, it’s actually genes from your mother’s side — the X chromosome — that determine penile size.

What else affects penis size, or can cause a small penis? If androgens, a group of sex hormones including testosterone, are low as the fetus grows, or the fetus has an abnormal hypothalamic or pituitary function, it could stunt penile growth

Some rare genetic conditions may affect penis size and fertility, including Kallmann syndrome and Klinefelter syndrome.

Delayed puberty can pose a concern for some children, as their penis can appear smaller than their peers. However, most adolescents experiencing a delayed growth spurt catch up to others their age by the time they’re 18.

Overall, there is not much you can do to control your penis size. Factors like your body shape and how much body fat you have, as well as the amount of pubic hair you have, can make your penis appear larger or smaller, without affecting actual size.

Does the penis get smaller with age?

The penis doesn’t actually shrink with age. However, it may look and feel slightly smaller while it’s erect.

The penis is made up of spongy tissue, and blood flowing into that tissue is what creates an erection. Therefore, blood flow to the penis is one factor that determines the size of an erection. As you age, you’re more likely to have fatty deposits in our arteries, reducing blood flow and penis size while hard.

Another factor impacting erection size is testosterone. Testosterone also declines naturally with age, potentially affecting how hard you can get. 

Can erectile dysfunction indicate infertility?

We've looked at penis size and fertility. What about erectile dysfunction (ED)? Can erectile dysfunction affect fertility?

ED is the inability to achieve or maintain an erection. It is extremely common, affecting around 30 million men in the United States. Studies show that ED is associated with poor semen quality, but this very much depends on what's causing the issue.

There are several physical and psychological causes of ED, such as:

  • Cardiovascular problems
  • Obesity
  • Specific medications
  • Low testosterone
  • Neurological disorders
  • Sleep disorders
  • Pelvic surgery
  • Stress, depression, and anxiety

Some of these underlying causes, such as obesity, low testosterone, sleep disorders, and stress, are also associated with infertility, explaining some of the relationship between infertility and erectile dysfunction.

When it comes to ED and fertility, the relationship is typically more indirect. ED can affect the chances of conception by inhibiting a person’s ability to maintain an erection, have sex, and have an orgasm — all required for natural pregnancy.

There are many treatment options for erectile dysfunction, depending on the root cause. If ED is hindering your ability to have sex and have a child with your partner, a doctor can guide you through the best fertility options for you. 

As well as treatment for ED itself, there are artificial reproductive techniques and sperm retrieval techniques to assist with getting pregnant, like:

Is there a connection between testicle size and male fertility?

Testicular size varies from person to person. The average diameter is around 4.5 to 5.1 cm. The role of the testicles is two-fold:

  1. To produce sperm 
  2. To secrete testosterone, the hormone associated with the development of male physical characteristics and sex drive

There is little research to link testicle size and infertility directly. Seminiferous tubules, tube-like structures that create sperm cells, make up 80% of the testicle volume. Therefore, testicular size has been associated with testicular function. In theory, you might produce less sperm if your testicles are much smaller than average.

Testicular atrophy, or shrinking of the testicles, can be a side effect of a hormonal imbalance, infection, or steroid use. This can have a detrimental effect on fertility. Additionally, undescended testicles — when a testicle(s) hasn’t “dropped” into the scrotum — has been shown to affect fertility.

Kallmann syndrome and Klinefelter syndrome, the aforementioned genetic conditions affecting fertility and penis size, may also result in smaller testicles.

It's normal for testicles to come in all shapes and sizes. It's also normal for one testicle to be a bit larger than the other, or for them to hang at different heights. As long as your testicles aren’t exceedingly small or large, your testicle size isn't going to have a significant impact on your testosterone levels or fertility.

The main consideration is to look for changes in your testicles. Check your testicles regularly. Make sure you look at them to see any changes visually. Roll the scrotum and testes slowly between your fingers, noting any hard lumps, bumps, or change in the size, shape, or consistency of the testicles. If you find anything new, or feel any pain or heaviness in your testicles, be sure to visit your doctor.

Some issues with the testicles can affect fertility:

  • Varicoceles. Around 40% of males with infertility have varicocele, an enlargement of the veins within the testicles.
  • Testicular cancer. Treatment for testicular cancer might affect fertility.
  • Testicular atrophy due to steroid use, hormone imbalance, or infection.

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The best way to understand your fertility is a semen analysis

The key takeaway here is that you shouldn’t be too worried about your penis or testicle size if you’re trying to get someone pregnant. If you have difficulty conceiving with your partner or are concerned about your fertility, a proactive first step is to have a semen analysis.

A sperm analysis can tell you:

These are all key parameters in determining your sperm health, impacting your chances of having a child with your partner. However, an abnormal semen analysis result doesn't mean you won't be able to have a child. Semen parameters may improve if you make changes to your lifestyle and overall health. 

A reproductive specialist can guide you through your sperm analysis results. They can help you understand how the results may impact your fertility, provide clinical advice, and discuss actionable day-to-day changes that can help you take control of your fertility.

Legacy’s semen analysis kit includes a complimentary virtual consultation with a fertility specialist to discuss your results and your fertility plans. Get started.


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