Blastocyst versus day 2 or 3 transfer.

The formulation of new sequential culture media, capable of supporting the development of viable human blastocysts, has reopened the discussion regarding the best day for embryo transfer following in vitro fertilization (IVF). Although several laboratories have reported overall increases in implantation rate and IVF efficiency following the transfer of blastocysts, others have failed to observe any benefit from extended culture. While culture conditions for the mammalian embryo undoubtedly have improved significantly over the past few years, relatively little attention has been paid to the quality of oocytes derived from ovarian hyperstimulation or the quality and receptivity of the endometrium following such hormonal regimes. It appears that differences in controlled ovarian hyperstimulation are among the major factors determining embryo quality and subsequent implantation. This therefore has confounded comparisons between different laboratories. In spite of this there are a growing number of reports demonstrating that the advantages of extended culture and blastocyst transfer, such as increased implantation rates, are not limited to specific groups of patients or specific etiologies. Rather, blastocyst transfer may be of benefit to the majority if not all patients attending for IVF.