Sperm delivery refers to the road sperm normally travels, from the testicles through to the penis. When a man does produce sperm, but it does not end up in his ejaculate, it is said that the azoospermia is due to a sperm delivery problem. This can have a number of reasons, often involving the tube that is supposed to carry sperm from the scrotum to the penis; the vas deferens. Some men don't have vas deferens, others have blockages, and in some cases, the tubes are not connected. This also applies to men who have had a vasectomy.
Men who have sperm production problems may suffer from a lack of essential hormones to make this process possible. Swollen, dilated veins in the testicles (called varicocele) can also cause sperm production problems. Depending on the causes of a man's azoospermia, the condition can sometimes be cured with hormonal medications or with surgical interventions. In cases where sperm is being produced but cannot be delivered, sperm extraction directly from the testicles can provide the man with a chance to have biological children, with the help of other fertility treatments. Intracytoplasmic sperm injection (ICSI) might be needed, because only limited amounts of sperm can be retrieved in this manner. If you would like to read more about male fertility problems, see erectile dysfunction and male infertility.