Culture and transfer of viable blastocysts: a feasible preposition for human IVF

In spite of the numerous advances in the field of human assisted reproducti ve technologies (ART) over the past 20 years, a rate-limiting factor in the overall efficiency of the procedure (the implantation rate) has remained a t 10-30%, The development of sequential media has led to the ability to cul ture routinely the human embryo to the viable blastocyst stage. Transfer of such blastocysts has resulted in a significant increase in implantation ra tes. Increases in implantation rates following blastocyst transfer have bee n reported for specific groups of patients culminating in the elimination o f high order multiple gestations. Of greater significance, however, is that the introduction of blastocyst transfer to all patients entering infertili ty clinics is associated with an overall increase in implantation and pregn ancy rates. Blastocysts derived from the use of sequential media are readil y cryopreserved and produce high implantation rates after transfer. Using a model to account for both total embryo utilization per cycle (transferred plus cryopreserved) and implantation rate, it has been calculated that exte nded embryo culture and blastocyst transfer is similar to 20% more efficien t than the transfer of cleavage stage embryos on day 3. Furthermore, as the score of the blastocysts obtained using sequential media is directly relat ed to implantation and pregnancy rates, it is possible to determine which p atients should be offered a single blastocyst transfer, thereby addressing the issue of twins conceived through ART.