Anatomic abnormalities, which obstruct the passage of sperm into the ejaculate; or lack of proper development of the internal reproductive organs
Hormonal abnormalities, where certain imbalances can affect the ability to produce sperm
Abnormal dilation, or expansion, of the veins in the testicle; also known as a varicocele, this abnormality is found in approximately 25-35 percent of infertile males during a physical examination.