Sperm washing for Intrauterine Insemination (IUI)
If you will be undergoing IUI, sperm washing is part of the treatment. After sexual intercourse, sperm has a long way to travel until it reaches en egg. By the time sperm reaches the uterus, chemicals called prostaglandins will naturally have been eliminated. That is just as well, because prostaglandins could cause strong uterine contractions if they were to come into contact with the uterus. Because IUI involves a direct injection of sperm into the uterus, sperm washing is necessary first, to eliminate prostaglandins. Healthy sperm can also be separated from those with an abnormal shape, size, or speed.
Sperm washing to prevent HIV transmission
If a man has been infected with the HIV virus, sperm washing can be used to prevent transmission of the virus onto his partner, and still allow him to become a father. HIV is transmitted mainly through seminal fluid, without being present in the sperm itself. Sperm washing does not eliminate every risk of transmission, but the risk is greatly reduced. Also see, when can you take a pregnancy test after IUI? and best fertility clinics for male infertility.