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MicroSort FAQ

How does MicroSort sperm sorting work?

There are two types of sperm in a man’s semen, X sperm and Y sperm. If an X sperm fertilizes the mother’s egg, a girl is conceived; if a Y sperm fertilizes the egg, a boy is conceived.

Chromosomes
Y chromosome is on the left, larger X chromosome is on the right

Because the X chromosome is larger than the Y chromosome, the X sperm has slightly more total DNA than the Y sperm -- about 2.8% more. MicroSort takes advantage of this fact to separate X sperm from Y sperm using a technique called flow cytometry.

Flow cytometry is a technique for analyzing and sorting microscopic particles, with uses in biology, pathology, and immunology (see flow cytometry in Wikipedia). MicroSort is an adaptation of this technique for human sperm.

  • Sperm are stained with a special fluorescent dye that attaches temporarily to the DNA in the sperm. Because an X sperm has 2.8% more DNA, slightly more of the dye will bind to an X sperm compared to a Y sperm.
  • Sperm are forced to travel, single file, through a "sheath" fluid.
  • The sperm pass through a laser, causing the fluorescent dye to glow. Brighter-glowing sperm cells are identified as X sperm, and sorted accordingly.
  • The result is an "enriched" sample, which is not 100% X or Y, but has a higher percentage of one or the other.
MicroSort machine
The MicroSort machine.

Note that sorting is based on this difference in fluorescence, caused by the greater amount of DNA in X sperm -- not sperm weight or size. MicroSort is the only method that is based on this measurable difference in DNA. Other “sperm spinning” techniques depend on the differences between the X and Y sperm that have not been proven to exist (such as weight).

The MicroSort procedure refers only to the sperm sorting process. After your enriched sample has been obtained, you'll still need to use it to become pregnant, by same procedures used by infertile couples: artificial insemination (IUI) or IVF.