The production of sperm is a complex process and requires normal functioning of the testicles (testes) as well as the hypothalamus and pituitary glands — organs in your brain that produce hormones that trigger sperm production. Once sperm are produced in the testicles, delicate tubes transport them until they mix with semen and are ejaculated out of the penis. Problems with any of these systems can affect sperm production.
Also, there can be problems of abnormal sperm shape (morphology), movement (motility) or function.
However, often the cause of low sperm count isn’t identified.