Effect of the position of the meiotic spindle on the outcome of intracytoplasmic sperm injection.

The position of the meiotic spindle in relation to the injection site has been a matter of concern since intracytoplasmic sperm injection (ICSI) was developed. Disruption of the spindle may result in cell death or aneuploidy, and it is therefore essential to avoid injecting directly into the area of the spindle. Before the development of the PolScope, it was only possible to visualize the spindle after fixing and staining oocytes. The PolScope allows the spindle to be visualized in living oocytes, and thus their subsequent development can be followed. Studies have shown that the spindle is not, as had been assumed, always adjacent to the polar body. However, the proportion of oocytes in which the spindle is significantly displaced is low, and the displacement is not necessarily associated with poor oocyte and embryo development. Even oocytes in which no spindle is visualized may go on to fertilize and develop normally, and the evidence indicates that disruption of the spindle is not a significant factor in determining the likelihood of aneuploidy and developmental anomalies. Indeed, it has been suggested that injecting spermatozoa closer to the site of the spindle may in fact improve the outcome.