Dr. Roger Lobo: Hi! I am Dr. Roger Lobo with the American Society for Reproductive Medicine, and today we are talking about causes of male infertility. Male infertility can be due to a variety of conditions. Some of these can be found and corrected, while others cannot be corrected. Most problems with male infertility occur when there are low numbers of sperm or abnormalities in their movement or shape. This can result from abnormalities in the production, transport, or delivery of sperm. A varicocele is common potentially correctable cause in male infertility. A varicocele is a collection of enlarged veins in the scrotum that can affect sperm production and its characteristics. Varicocele occur in about 15% of all men and as many as 40% of those who are infertile. Dr. Janet Choi: The tricky thing with that area is, that there are lot of fertile men who are found of varicocele, so what do you do with that when you find a small one of it in an infertile male, and this is when a male might first want to consult with the urologist before acting on, taking care of varicocele, which sometimes might require surgery. Dr. Roger Lobo: About 10 to 15% of men with low sperm counts have an abnormality in the Y chromosome, which affects the development of sperm. Others maybe born without critical parts of the sperm transport process, such as the vas deferens, which connects the testis to the male urethra. Vasectomy is a common surgical cause of male infertility in men who have changed their minds about fertilization, but men who have had other surgery in or near the reproductive track also can have problems. Injury to the nerve supply and/or obstructions in the transport system can affect sperm production. For some men, fertility is affected by abnormal hormones too. Too much estrogen and/or too little testosterone can negatively affect the development in maturation sperm. Other hormones maybe involved as well. Temperature also plays a critical role. Sperm can only mature at temperatures lower than the whole body temperature. This is why the testis normally lies in the scrotal sac outside of the body. Heat exposure or conditions where the testes have not descended into the scrotum can affect sperm production. Male infertility can also be due to infections, certain medical conditions and exposure to toxins such as chemotherapy or radiation. To learn more, check out our other videos on fertility, including the basic infertility evaluation.