Fertilization of oocytes by injecting spermatozoa, spermatids and spermatocytes

The feasibility of fertilization by injecting spermatozoa into oocytes has increased significantly the possibilities for treatment of severe male infertility. However, the rapidity of human application has raised some concern about potential health hazards for the progeny. Human pregnancies and births have also occurred with the use of immature spermatozoa and spermatids, and normal offspring have been born after the injection of secondary spermatocytes into mouse oocytes. This short review deals with the problems that may arise from the injection technique and from the use of deficient or immature sperm cells for fertilization, with particular attention to human applications. Tests for screening parents and follow-up of children are suggested to control the main suspected risk factors.