The road to blastocyst transfer

Transfer of human embryos at the blastocyst stage is certainly not a 'new' concept or technique.Blastocyst stage transfers for patients with repeated implantation failures following in-vitro fertilization (IVF) treatment have been routinely and successfully practised by several groups around the world (Me ´ne ´zo et al., 1992a;Olivennes et al., 1994;Bongso et al., 1995).For this particular class of patients, transfer at the blastocyst stage may have been a more effective treatment option than the traditional day 2 or 3 transfer.Whether this benefit was the result of better embryo selection, better embryo development in vitro because of embryotrophic factors released by co-culture cells, or more synchronous transfer to the uterus is impossible to distinguish.The endpoint was simply to achieve pregnancies in a difficult subset of patients.