Gender selection using Microsort provides the ability to sort male and female sperm.  The sperm absorb a dye, which attaches temporarily to the DNA inside the individual sperm. When exposed to laser light, the dye becomes fluorescent.

Since the X chromosome is larger than the Y, there is more DNA for the dye to attach to and, consequently, the sperm with the X chromosomes will appear brighter than those with Y-chromosomes. A flow cytometer, similar to a microscope, is able to pick up these differences in brightness and separate the sperm as they move through the machine one at a time. 

Once the Microsort technique is complete, the sorted sperm are introduced into the uterus during an intrauterine insemination (IUI) procedure. Currently, MicroSort sperm sorting technology improves the chance of a female pregnancy to 89.5%, and a male pregnancy to 73.6%.

HRC Fertility is one of two fertility centers in the United States authorized by the Food and Drug Administration to offer Microsort as a part of a national study. However, physicians worldwide send sperm to these two centers for sorting.