Infertility is defined as the inability of a couple to get offspring after one year of intercourse without using any type of contraception. According to different estimates, 10–15% of couples are coping with involuntary childlessness. The birth of the first IVF (in vitro fertilisation) baby opened up a completely new frontier in medical treatment of infertility. Pregnancy rates have constantly improved during the last ten years and nowadays the success rates of around 25-30% are routinely reported by majority of IVF programmes.
Unfortunately, the need to increase pregnancy rate has led to transfer of multiple embryos resulting inunacceptably high (~30%) multiple pregnancy rate. In order to achieve total elimination of multiple pregnancies only a single embryo should be transferred. Transferring one embryo requires extremely careful evaluation of embryo quality. Traditionally, embryos are selected for transfer two days after insemination considering simultaneously their morphological appearance and growth rate. More promising future strategies for embryo selection can, however, be based on preimplantation genetic diagnosis.