Sperm sorting

Sperm sorting is a means of choosing what type of sperm cell is to fertilize the egg cell. Several conventional techniques of sperm sorting have been routinely used in assisted reproductive technologies including the method of density gradient centrifugation or swim-up. Newly applied methods such as flow cytometry expand the possibilities of sperm sorting and new techniques of sperm sorting are being developed.

It can be used to sort out sperm that are most healthy, as well as for determination of more specific traits, such as sex selection in which spermatozoa are separated into X- (female) and Y- (male) chromosome bearing populations based on their difference in DNA content. The resultant 'sex-sorted' spermatozoa are then able to be used in conjunction with other assisted reproductive technologies such as artificial insemination or in-vitro fertilization (IVF) to produce offspring of the desired sex - in farming animals but also in human medical practice.

Several methods have been used to sort sperm before the advent of flow cytometry. Density gradient centrifugation (in a continuous or discontinuous gradient) can concentrate semen samples with low concentration of sperm, using the density of sperm as a measure of their quality. Similarly, so-called swim-up techniques apply a centrifugation step and then sperm is allowed to swim up into a medium, thus enriching a subpopulation of motile sperm. However, use of sperm centrifugation is detrimental to the sperm viability and elicits production of reactive oxygen species. Conventional techniques are routinely used in assisted reproductive technology.

Flow cytometry is another method used to sort sperm and adaptations of this technique opens new opportunities in sperm sorting. However, because flow cytometry-based sperm sorting often uses fluorescent dyes that often stain DNA, the safety of this technique in human reproductive medicine is a matter of scientific discussion.

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