What is the fine-grained topic of the following text: Male factor fertility can result in a variety of issues such as complete absence of sperm in the ejaculate (azoospermia) due to either an obstruction/blockage (obstructive azospermia) often caused by a previous vasectomy or congenital-birth defects or failure of sperm production by the testicles (non-obstructive azospermia). Only return the topic.
Male factor fertility and causes of azoospermia