What is sperm washing? How is it done?

L.

Semen is made up of sperm cells, seminal fluid and debris (dead sperm, white cells, mucus and fat globules). When we do intrauterine insemination (IUI), we are most interested in getting motile, healthy sperm cells into the uterus.

However, we can't just shoot raw semen right from the cup directly into the uterus. The sperm swim in a liquid called seminal fluid, predominantly produced by the prostate gland, which contains chemicals called prostaglandins. Prostaglandins are responsible for smooth-muscle contraction and are involved in many body processes. They are also responsible for causing monthly menstrual cramps. Prostaglandins are present at very low levels in many places in the body. The amount in seminal fluid, however, is at a very high concentration. When semen enters the vagina during sex, the prostaglandins cause no problem. But if we injected raw semen directly into a woman's uterus to try to get sperm to the egg, she would experience severe pain and perhaps even vascular collapse and death.

So the goal of sperm washing to separate healthy sperm from this potentially toxic seminal fluid. This is done through several different methods. The simplest is to dilute the semen with a nutrient medium, put it into a tube, and put the tube into a centrifuge -- a device that spins the tube to separate the mixture into various layers. The good sperm are left in the bottom of the tube and can be drawn into a syringe for insemination. Other methods involve the use of media of varying densities. The sperm are layered on top of these special media and spun in a centrifuge. This processing step results in selection of only the most active sperm and culls out some of the debris that may not be removed in the simpler sperm-washing procedure. Other methods are sperm swim-up and swim-down, which are modifications of the above procedures. These procedures may take between 30 and 90 minutes to perform.

Why do we go through all of this just so we can put the sperm directly into the uterus? Because intrauterine insemination overwhelmingly provides a better chance of pregnancy than simply placing sperm in the cervix. In fact, there really is no longer much place for cervical insemination. IUI can help in cases of unexplained infertility, male-factor infertility, endometriosis-related infertility, cervical stenosis, and antisperm antibodies.