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The use of cryopreserved mature and immature spermatozoa in assisted reproduction.

Treatment of severe male subfertility has become available since the intracytoplasmic injection of a single sperm into an oocyte was successfully applied for the first time in 1992. Moreover, with the use of fresh and cryopreserved epididymal and testicular spermatozoa for this procedure, fertilization and pregnancies could be accomplished. This review addresses the development and performance of these techniques and discusses achievements and problems as well as future aspects of the feasibility of early spermatid injection. Furthermore, limitations of these procedures and concerns with regard to genetic and epigenetic risks of using immature gametes are discussed.