The successful introduction of ICSI for the alleviation of male-factor infertility must surely be one of the most significant advances in reproductive medicine since the birth of Louise Brown back in 1978 (Palermo et al., 1992). Patients presenting with semen containing either too few sperm and/or sperm with poor progressive motility are obviously good candidates for ICSI. Also, it is well known that sperm that have a normal shape, as determined by morphological criteria, are more likely to bind to and therefore fertilize eggs; therefore, ICSI may be warranted where there is a very low percentage of morphologically normal sperm within the semen. However, routine IVF can also fail despite apparently excellent semen parameters, presumably for biochemical reasons. Again, ICSI offers a suitable remedy should this prove to be a consistent problem that cannot be attributed to poor egg quality alone. Nevertheless, ICSI must still mimic the latter stages of fertilization in vivo if it is to prove successful.

Essentially, as with gamete fusion, both cell membranes (i.e. the oolemma of the egg and the plasmalemma of the sperm) should be temporarily breached, so it is necessary to ensure that the oolemma has been penetrated, as is evident by a sudden free flow of ooplasm, and that the plasmalemma has been ruptured, as is evident by permanent immobility of the sperm tail. Considering these requirements, ICSI is technically demanding and there is substantial potential for damage to the egg, which can cause it to degenerate.