In couples who do not conceive, the man plays a part in roughly half of cases. That is what a 2021 review in The Lancet reports (PMID 33308486). Globally it affects 8 to 12 percent of couples.
Yet the workup still often starts with the woman. I find that a curious habit, because checking the man is by far the simplest and least invasive part of the whole process.
There is something else men rarely hear. You almost never feel any of this.
What causes male infertility?
It nearly always goes wrong in one of three places. Too few or poorly moving sperm are made, they cannot get out because of a blockage, or the hormonal signal from your brain is off. In a substantial share of men, no clear cause is found even after all the testing.
Those three places are a useful hook, because they line up with what you can measure.
| Where it goes wrong | Examples | What you often see alongside |
|---|---|---|
| Production in the testicle | Varicocele, past infection, chemotherapy, congenital factors, an undescended testicle in childhood | FSH may rise, inhibin B may fall |
| Transport out | Blockage of the vas deferens, consequences of an STI, after a vasectomy | Hormones can be entirely normal |
| The signal from your brain | Too little LH and FSH, a raised prolactin, use of anabolic steroids or testosterone | LH and FSH low, testosterone often too |
| No identifiable cause | Everything looks normal, the semen analysis does not | More common than men expect |
That third row deserves a warning you rarely hear on a gym floor. Testosterone from outside, whether that is a cycle or prescribed therapy, shuts down your own production.
Your brain sees enough testosterone and stops sending LH and FSH. Without that signal, sperm production in the testicle falls back, sometimes to near zero.
For many men that is a painful surprise, arriving exactly when they start wanting children.
Can you notice male infertility?
Usually not. There are rarely any symptoms: your erections are normal, your interest in sex is normal, your ejaculate looks normal, and the volume of fluid says nothing about the number of sperm in it. For most men, a disappointing semen analysis is the first and only clue.
Semen is mostly fluid from your prostate and seminal vesicles. The sperm themselves are microscopic, and you cannot see their number with the naked eye.
So no conclusion rests on that at all.
There are exceptions. A heavy feeling or a bundle of veins above your testicle may point to a varicocele. A past bout of epididymitis can leave scarring in the outflow tube.
But as a rule of thumb: no symptoms means nothing here. That is exactly why men place themselves outside the investigation so easily.
Which hormones matter for fertility?
Four values tell you the most together. FSH and inhibin B cover sperm production, LH and testosterone the hormone side. A raised prolactin can disturb the signalling.
FSH and inhibin B move against each other, and that is precisely what makes them useful.
In a Danish study of 349 men, inhibin B tracked positively with sperm concentration while FSH moved the other way (PMID 9398713). Men with a low inhibin B and a high FSH at the same time nearly always had a low sperm concentration.
Picture two men with the same disappointing semen analysis. In the first, FSH is high and inhibin B low: the testicle is getting the order but not delivering.
In the second, FSH and LH are both low: no order is arriving at all. The same result, a completely different story, and a completely different conversation with the doctor.
How those two factories in your testicle work is explained in testicles: how they work.
What does lifestyle do to your fertility?
Less than the supplement industry promises, and more than nothing. Smoking, heavy drinking, significant excess weight and anabolic steroid use are all linked in research to less favourable sperm quality. How much you gain by changing varies enormously per man and is rarely predictable.
With heat, the difference between mechanism and advice matters.
That sperm production wants to run a few degrees below your core temperature is well established, and the effect of heat is largely reversible (PMID 25456164). That your laptop or your underwear actually makes the difference is far more thinly supported.
One study measured a rise in scrotal temperature of around 2.8 degrees in laptop users (PMID 15591087), but measured no sperm at all.
One more thing worth remembering: a sperm cell takes about 72 days to mature. So what you change today shows up in a result three months from now at the earliest.
Anyone who retests six weeks later and feels disappointed is simply measuring too early.
What testing can you have as a man?
The semen analysis is the foundation, and hormones fill it in. A semen analysis looks at the number, the movement and the shape of your sperm. Since 2021 the WHO has used lower limits including 16 million sperm per millilitre and 30 percent progressive motility.
Those limits are fifth percentiles from men who fathered children, and therefore not a dividing line between fertile and infertile.
Sitting below the limit means the odds are lower, not that it is ruled out. Sitting above it is no guarantee either.
How to read such a result is set out in our piece on semen analysis values. The steps you can take with your GP when it is not happening are described in trying to conceive.
Some men choose to get the hormonal side in view early. The IVF partner screening and the Hormones Man panel look at those values.
A blood test does not replace the semen analysis, and the full story starts with our guide to male fertility. Discuss your results with your GP, who can help you decide whether further steps make sense.
If it has not worked for a year, just get yourself looked at alongside her. It costs you a cup and a vial of blood, and it saves months.
References
- Agarwal A, et al. Male infertility. The Lancet. 2021. PMID 33308486.
- Jensen TK, et al. Inhibin B as a serum marker of spermatogenesis. J Clin Endocrinol Metab. 1997. PMID 9398713.
- Boitrelle F, et al. The Sixth Edition of the WHO Manual for Human Semen Analysis. Life (Basel). 2021. PMID 34947899.
- Durairajanayagam D, et al. Causes, effects and molecular mechanisms of testicular heat stress. Reproductive BioMedicine Online. 2015. PMID 25456164.
- Sheynkin Y, et al. Increase in scrotal temperature in laptop computer users. Human Reproduction. 2005. PMID 15591087.
- Thuisarts. Pain in your scrotum. thuisarts.nl
Every blood test result at Caliber includes a professional assessment by a BIG-registered doctor. For treatment decisions, always discuss your results with your GP.
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