After the embryologist has checked your eggs, he or she moves on to your sperm sample, which in most cases is produced on the day of egg collection (refer to Chapter 5). Sperm need a bit of cleaning up and sorting before they are added to the eggs.
The ejaculate consists of sperm mixed in secretions from the seminal vesicles and the prostate called seminal plasma, as well as white blood cells, dead sperm and other 'debris'. The live sperm need to be separated out from this other material before they can be added to the eggs. To do this the embryologist places a layer of special culture medium over the sperm sample. The motile sperm are able to swim through this layer, leaving behind the unwanted material at the bottom of the container. The embryologist then skims the motile, cleaned sperm off the top.
After the motile sperm have been removed they are diluted with culture medium, placed in a test tube and centrifuged (spun) by machine. As they are spun, the best sperm gather as a pellet at the bottom of the test tube. This pellet is harvested and the process is repeated. The end result is a small volume of fluid with a high concentration of motile sperm, perfect for the waiting eggs.
If you have a male factor infertility problem, you'll probably have the intracytoplasmic sperm injection (ICSI) procedure rather than IVF. Sperm preparation techniques for ICSI vary depending on what kind of problem you have and whether sperm are in the ejaculate or surgically retrieved from the testicles. (I explain the different ways of retrieving sperm from the testicles in Chapter 5.)
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