[Prognostic factors of implantation].

One of the negative aspects of in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) is the increased risk of multiple pregnancies. There is an epidemic of twin pregnancies with a higher risk of obstetric, perinatal and neonatal complications than singleton pregnancies and with an important psychosocial, economic and financial impact for the parents to be. A reduction in the number of twins can only be obtained by the transfer of one embryo. Single embryo transfer with an acceptable pregnancy rate might be considered if a top quality embryo is available. The need to characterize embryos with optimal implantation potential is obvious. A top quality embryo is characterized by the presence of 4 or 5 blastomeres at day 2 and at least 7 blastomeres on day 3 after insemination, the absence of multinucleated blastomeres and<20% cellular fragments on day 2 and day 3 after fertilization. Others prognostic factors of implantation are discussed in this review. Judicious application of eSET can halve the twinning rate while maintaining the overall pregnancy rate.