After the egg and sperm collection, the fertilization takes place at the same day into the laboratory. Ova and spermatozoa are placed in a special culture medium; if there are no problems in the spermatozoa, the latter fertilize the ova. The next day the success of fertilization is evaluated (i.e. the number of embryos that have occurred), the couple is informed about the results, and the embryo transfer day is scheduled. Until then, the embryos remain in the appropriate culture media and grow by continuous cell divisions.

The application of this technique is essential for couples facing serious sperm disorders. This is because in such cases the spermatozoa may not be able to fertilize the ova during in vitro culture.Thus with the help of special micro-instruments a small cut is done on the oocyte’s surrounding zona and a spermatozoon is inserted into it, offering great chances of fertilization. The ICSI technique should be performed only when this is necessary as this involves a larger degree of intervention.