A few hours after oocyte retrieval, oocytes are fertilised by the sperm sample as follows: the sample is prepared by the embryologists in the laboratory and an adequate amount of the processed sample is mixed with all of the oocytes.
Oocytes and sperm cells are incubated together under the appropriate conditions, resembling those in natural conception. Fertilisation is checked the next morning: 2 pronuclei are detected in fertilised oocytes. Average fertilisation rate reaches 65-70%, i.e. if one couple has 10 oocytes, 6-7 of them are expected to be normally fertilised (formation of 2 pronuclei).
Fertilisation rate may vary among couples; sometimes, it may be increased or reduced for no particular reason. There are couples with very low fertilisation rate or no fertilisation at all. If fertilised oocytes are few, but develop into good quality embryos, pregnancy achievement rates are equally good.
Total failure to fertilise is possible, although rare. In that case, unfortunately, there are no embryos to be transferred. If that happens unexpectedly, the next step is an appointement of the couple with Mr. Evripidis Mantoudis and the embryologists at “gennima”, to jointly plan the next moves. Sometimes, some additional tests are required. Failed fertilisation may be due to oocyte quality, sperm quality or even to difficulties in combining oocytes and sperm. In some cases, it is deemed necessary to proceed with ICSI (see below) in a future IVF cycle. However, it is important to stress that ICSI cannot offer solution in all cases either; this technique may fail too, especially if the problem is detected in the oocytes.
The above procedure is called “classic in vitro fertilisation” (classic IVF) and is used when the sperm sample is of “good quality”, i.e. with various parameters (volume, sperm count, motility, morphology) at normal levels. If the sperm sample is of lesser quality (low sperm count, low motility, etc.), the technique of ICSI is used (see below).
However, within the framework of IVF in the laboratory and if allowed by sperm quality, natural fertilisation (classic IVF) is preferred, because natural selection is preserved: like in natural fertilisation at home, the strongest sperm will be able to fertilise the oocyte. With ICSI, the concept of natural selection is set aside, as embryologists select one sperm among hundreds of other, identical ones; i.e. the human factor is involved.