Sperm deposition site during ICSI affects fertilization and development.

OBJECTIVE: To evaluate the effects of sperm placement during ICSI relative to the M-II spindle location on fertilization and preimplantation development.

DESIGN: Retrospective analysis of oocyte fertilization and embryo development with respect to sperm deposition site during ICSI.

SETTING: A program of IVF-ET.

PATIENT(S): Seven hundred seventy-six patients.

INTERVENTION(S): Egg quality, sperm deposition site, and polar-body position were recorded during ICSI; fertilization was assessed on day 1; embryo development was evaluated on days 2 and 3.

MAIN OUTCOME MEASURE(S): Fertilization, embryo development, and implantation rates.

RESULT(S): Normal fertilization is not affected by polar-body orientation, with the exception of a significantly lower fertilization rate from a 9 o'clock polar-body orientation. Injections with the polar-body positioned at 7 or 11 o'clock result in the greatest number of high-quality embryos, significantly more than the adjacent 6 or 12 o'clock polar-body orientations and irrespective of oocyte anomaly frequency. Embryos originating from the 7 or 11 o'clock polar-body category implant at a higher rate, although the data are not significant.

CONCLUSION(S): The placement of the sperm during ICSI relative to the presumed location of the meiotic spindle significantly impacts fertilization and high-quality embryo development. Sperm deposition in the M-II spindle area should be avoided. It appears that development, and not fertilization, is improved by decreasing the distance between the sperm cell and the spindle.