Micro-insemination: Genetic aspects

Abstract

Micro-insemination involves sperm deposition directly into oocytes. This can be by transfer of sperm (Micro-Insemination Sperm Transfer, or MIST) or by micro-injection into the ooplasm (Micro-Insemination Micro-Injection into Cytoplasm, or MIMIC). Micro-insemination is indicated in spermatozoa with no or very poor motility, very low density, multiple defects, or inability to penetrate oocyte vestments. There is a 10% incidence of chromosomal abnormalities in spermatozoa from fertile and normal men. However, there is no increase in sperm chromosomal abnormalities in men with normal peripheral karyotypes and highly abnormal sperm parameters. Preliminary results of karyotypes of human oocytes that failed to become fertilized after MIST and mouse morulae and blastocysts produced after MIST reveal that there was no significant increase in aneuploidy or polyploidy. There is evidence that MIMIC may result in increased abnormal sperm karyotypes. Polyspermy is low in the mouse and human after transfer of multiple spermatozoa into the perivitelline space, thus suggesting an oolemmal block. However, blastomere membranes do not fuse with spermatozoa, as observed in a study of MIST into human embryos. Zona drilling with acid is not advised because of disturbances to chromosomal kinetics. The conclusion of this review is that MIST does not result in an increased risk of chromosomal abnormalities, while caution must be exercised with MIMIC.