What does “sperm washing” mean?

It is sometimes also called sperm preparation or spinning. It is a laboratory technique for separating sperm from semen, and separating motile sperm from non-motile sperm, for use in assisted reproduction (IUI, IVF).

The washing technique for near normal specimens is mixing the ejaculate after liquefaction with the appropriate washing medium followed by centrifugation. (A centrifuge is a machine that separates materials with different densities by spinning them at high speed.) The supernatant is discarded and the sediment (sperm rich fraction) is re-suspended in more washing medium. This process is repeated 2-3 times maximum. In the final wash, the sediment is re-suspended in 0.5 cc of medium, loaded into a syringe and deposited in the uterus.

The “Sperm Rise” or “Swim-up” technique is one in which two to five cc of medium are carefully layered on top of 0.2-0.5 cc of semen. Motile sperm cells “swim-up” into the culture medium. After some time (30-90 minutes) the medium (containing motile sperm cells) is carefully harvested and centrifuged. If necessary, fresh medium is layered on top of the seminal fluid again to harvest more sperm cells.

The discontinuous gradient centrifugation technique utilizes a dense liquid phase to separate sperm cells from seminal fluid and debris. There are different compounds commercially available that may be used. Semen is deposited on top of this fluid and subjected to centrifugation. Motile sperm cells migrate to the bottom of the tube, which are used for IUI after further washing.