Human preimplantation embryo development in vitro: a morphological assessment of sibling zygotes cultured in a single medium or in sequential media

A comparison was made of the development of human zygotes in either a one-step (Global (R) medium) or two-step culture system (Quinn's Advantage (R)). A total of 257 normally fertilized 2PN zygotes from 28 patients were used in the study. The study was broken down into two parts: the first concerned the development of embryos from Days 1 to 3 in Global (R) medium and Quinn's Advantage (R) cleavage medium; the second consisted of a comparison of the development of embryos from Day 3 to 5/6 in Global (R) medium and Quinn's Advantage (R) blastocyst medium. There were no significant differences between the two culture media with respect to embryo quality throughout the preimplantation phase of human embryo development as determined by the extent and variability of the cell counts, fragmentation, and nucleation. A difference was noted in the blastomere symmetry of Day 2 embryos in the two media, but was no longer apparent on examination of Day 3 embryos. No differences were noted in the rates of blastocyst development, inner cell mass (ICM), and trophectoderm (TE) scores in the two culture media. Finally, no significant differences were noted with either the proportion of blastocysts chosen for transfer or cryopreservation (vitrification). The findings support the view that two-step sequential media protocols are sufficient but not necessary to support the complete in vitro development of human preimplantation embryos.