The retrieved eggs are taken into the IVF laboratory where they are prepared for insemination. At the same time, the semen is activated to improve its fertilisation potential. Oocytes and spermatozoids are placed together for several hours within an incubator which provides the ideal conditions for fertilisation to take place and the subsequent development of pre-embryos. The number of fertilised eggs will not be known until the next day but the overall fertilisation rate is 60%. For this reason several embryos usually develop.