Semen that has been centrifuged and no sperm detected for 3 or more times becomes azoospermia. Azoospermia is divided into obstructive and non-obstructive azoospermia according to the presence or absence of normal spermatogenesis in the testes. Obstructive azoospermia (OA) refers to azoospermia in which the spermatogenic function of the testes is normal but the transport of sperm is impaired by obstruction of the vas deferens. It can occur anywhere from the testis to the ejaculatory duct and can be subdivided into intra-testicular obstruction, epididymal obstruction, vas deferens obstruction, and ejaculatory duct orifice obstruction. Non-obstructive azoospermia is due to abnormal testicular spermatogenesis, while some patients have a mixed type with both spermatogenic dysfunction and spermatic tract obstruction.