Blastocyst versus early cleavage embryo transfer: a retrospective analysis of 4,165 transfers

To compare the clinical outcomes after the transfer of blastocysts versus early cleavage embryos in assisted reproduction technologies (ART). A retrospective analysis of all the ovarian stimulation-in vitro fertilization-embryo transfer cycles performed at the Centre for Human Reproduction, Athens, Greece, between June 1997 and December 2001. The number of blastocysts transferred per ET was significantly lower compared to that of all early cleavage embryos. The implantation rate of blastocysts was significantly higher compared to that of all other modes of transfer. Clinical pregnancy rate after the transfer of blastocysts was significantly increased compared to that after transfer of any early cleavage embryo. The viable pregnancy rate after the transfer of blastocysts was significantly increased only compared to that after the transfer of day-2 embryos. There were no significant differences regarding the multiple gestation rates among the various modes of transfer. The use of blastocysts in ART is beneficial when compared to that of day-2 embryos and at least comparable to that of day-3 embryos. Blastocyst culture and transfer remains a favourable and promising option in ART.