Sex-selection of human spermatozoa: evolution of current techniques and applications

Methods claiming to achieve sex selection by sperm sorting have existed for many years. Numerous applications for safe and effective selection procedures exist in current clinical practice, as sex-linked conditions could be theoretically eliminated by use of appropriate sperm for fertilization or insemination. Use of such techniques could also address the need to effect family balancing for some couples. Modern preconception sex-selection methods may be classified into two general types: those that attempt to segregate spermatozoa on the basis of subtle physical or kinetic features, and those that rely on distinctive nuclear characteristics unique either to X- or Y-chromosome bearing sperm. Laboratories providing sperm sexing using the former method have been available for some years, although the associated efficiency and reproducibility are controversial. Sex selection of spermatozoa by chromatin differences has been shown to achieve significant enrichment of X- or Y-chromosome bearing sperm, but clinical experience in humans is limited. The fundamental elements of the two approaches introduced here are reviewed and compared. Selected key historical concepts in sex selection by sperm sorting are outlined, followed by a summary of promising areas for future research.