To overcome the still insufficient implantation rate following in vitro fertilization (IVF) in humans, more than two embryos are commonly replaced which potentially leads to a high number of multiple pregnancies with associated risks such as low birth weight. The solution for avoiding multiple pregnancies could be optimalization of embryo selection and single embryo transfer.
The traditional systems for assessing gamete and embryo viability have limited ability to accurately select those with the best developmental potential. Morphological evaluation remains the primary method of oocyte and embryo assessment during IVF cycles.
However, its modest predictive power and inherent inter- and intra-observer variability limits its value. Prolonged embryo culture to blastocyst stage was introduced as a possible strategy for selecting the best embryos but on the other hand the extended period of in vitro culture may have its side effects.