ABSTRACT
The development of detailed scoring systems for the pronucleate oocyte and cleavage stage human embryo have undoubtedly increased the efficacy of human IVF.1-9 The advent of more physiological culture media, together with improvements in embryo culture systems and the laboratory, has now made it possible to culture the human embryo to the viable blastocyst stage as a matter of routine.10-13 There appear to be numerous advantages associated with extended culture and blastocyst transfer (Table 7.1). The current status of clinical blastocyst transfer has recently been analyzed,30 with the conclusion that extended embryo culture results in an increase in implantation and clinical pregnancy rates and a reduction in pregnancy loss in several subpopulations, especially patients under the age of 3731,32 and oocyte donors,33 as well as those patients with poor quality embryos,34 or who have experienced multiple IVF failures.35 Furthermore, it appears that the blastocyst stage of development more readily maintains its viability postcryopreservation than the pronucleate oocyte or cleavage stage embryo, making it the logical stage at which to freeze or vitrify embryos.28,36,37
Taken together, blastocyst culture facilitates a reduction in the number of embryos transferred, while increasing the success of cryostorage, thereby increasing the overall efficacy of an IVF cycle.29
