Embryo development and chromosomal anomalies after ICSI: effect of the injection procedure.

Intracytoplasmic sperm injection (ICSI) is a delicate procedure requiring considerable skills of the person performing it. Theoretically, the injection procedure could damage cytoplasmic structures in the oocyte, resulting in sublethal cellular injury and/or numerical chromosomal abnormalities that could lead to impaired embryonic development. In the present study, features of the injection procedure were evaluated in a total of 2924 oocytes from 305 cycles. Development to the blastocyst stage was found to be compromised in a group of surplus embryos originating from oocytes in which >6 pl of cytoplasm was aspirated into the injection pipette during the ICSI procedure. Characteristics of the injection procedure as well as blastocyst development of surplus embryos was shown to be significantly different between the four technicians performing the ICSI. Neither the volume of cytoplasm aspirated during the injection procedure, nor the position of the polar body (6 o'clock or 12 o'clock) influenced the mean incidence of disomic cells per blastocyst as revealed by fluorescence in-situ hybridization using probes specific for chromosomes X, Y and 18. In conclusion, certain technical aspects of the injection procedure can affect subsequent embryonic development to the blastocyst stage, but do not seem to influence the rate of chromosomal abnormalities that occur in human pre-implantation embryos.

The protective effects of polymers in the cryopreservation of human and mouse zonae pellucidae and embryos.

OBJECTIVES: To evaluate the occurrence of injury due to physical factors in embryo cryopreservation and the effect of the polymers dextran, polyvinylpyrrolidone (PVP), and Ficoll on this mechanical damage. DESIGN: Damage to the zona pellucida (ZP) observed after cryopreservation was taken as indication of cryoinjury caused exclusively by physical factors. Human and mouse ZPs from oocytes remaining unfertilized after previous IVF attempts and mouse two-cell embryos were frozen in the presence of different polymers. After thawing, they were checked carefully for signs of physical damage (cracks). A possible toxicity of the use of the polymers in cryoprotection was evaluated by development to the blastocyst stage of mouse two-cell embryos that survived the freezing and thawing process. RESULTS: Incidences of damaged ZPs in groups of human and mouse ZPs and two-cell embryos frozen without polymers were found to vary between 20% and 29%. The use of any of the tested polymers resulted in significantly lower incidences of damaged ZPs (0% to 15%). Damage to the ZP after freezing and thawing in mouse embryos was accompanied by low survival rates of the embryo itself. Of mouse embryos that survived the cryopreservation process, blastocyst formation was not significantly different in groups frozen without polymer (80%) or in the presence of either dextran (90%) or Ficoll (82%); however, embryos frozen in the presence of PVP showed low blastocyst formation (12%). CONCLUSIONS: Polymers can protect embryos against cryoinjury by avoiding mechanical strain occurring during cryopreservation. Polyvinylpyrrolidine is toxic to mouse two-cell embryos when present during freezing and thawing.