Causes of Male Infertility

https://www.testosterone.me/causes-male-infertility

It may seem simple, but the process of conception is somewhat complicated even for men. For a man to conceive, some thresholds must be met:

A man must have healthy sperm, capable of fertilization. This requires the adequate release of testosterone, as well as other hormones such as luteinizing hormone and follicle-stimulating hormone.

That sperm has to be able to mix with semen and pass through the tubes of the vas deferens without obstruction.
He must produce a sufficient amount of sperm to have a significant chance of conception. The lower a man's sperm count is, the harder it will be for him to get his partner pregnant. If a man produces fewer than 39 million sperm per orgasm or 15 million sperm per milliliter, he is very likely to have issues with conception.

That sperm must have functional mobility. It is normal that a small portion of sperm will have issues moving correctly, but the higher that this percentage is, the less likely that healthy sperm will make it successfully to the egg.