Preconceptional sex selection: Past, present, and future

Predetermination of sex in human and in farm animals is reviewed. Preconceptional sex selection has generated great interest and controversy over the years. Medical and commercial benefits outweigh the ethical issues. Technology has not yet provided a routine method for separating the X- and Y- chromosome-bearing sperm. Flow cytometry is the only technique that produces a clinically significant enrichment of X- or Y-bearing spermatozoa. However, concern has been raised about the methodological implications of the flow technique because of the use of DNA stains and UV light. Some other techniques, such as gradient columns, appear to produce a slight enrichment of one type of sperm over the other, but this level of enrichment appears unlikely to affect the sex ratio at birth. It thus remains speculative whether 100% pure preparation of X or Y sperm can be obtained unless a major improvement in methodology is achieved. Fluorescence in situ hybridization (FISH) and polymerase chain reaction (PCR) are currently the methods of choice for evaluating the validity of the sex selection procedure. In view of the extraordinary pace of the technological and scientific progress, it can be expected that the clinical and commercial application of the technology of preconceptional sex selection by X and Y sperm separation will be a reality in near future.