What is the most relevant standard of success in assisted reproduction? Should BESST really be the primary endpoint for assisted reproduction?
A major problem in IVF procedures is a high rate of induced iatrogenic complications including multiple gestations. Until now, transfer of at least three embryos followed by the subsequent elective reduction of triplet or higher order gestations to twins, single embryo transfer (SET) with cryopreservation of the remaining embryos, as well as the application of SET in unstimulated cycles, serves to illustrate the diversity characterizing the worldwide effort of achievement of pregnancy that aims to avoid possible complications. The BESST (birth emphasizing a successful singleton at term) endpoint constitutes an interesting parameter imposing the safety of SET. However, the observed success rate (11.1%) requires elucidation of the specific pattern of endometrial behaviour around the implantation window as well as its involvement in the further support of gestation. Consequently, research has to focus primarily on the improvement of technical parameters to achieve an acceptable success rate during the IVF procedures as compared with spontaneous gestations.