Developmental capacity of different morphological types of day 5 human morulae and blastocysts.

After prolonged culture of human embryos, the expanded blastocysts with oval inner cell mass (ICM) and cohesive trophectoderm (TE) are preferably selected for transfer. In cycles with poor embryonic development, the selection has to be done from among suboptimal blastocysts for which no grading system exists. In this study, 1396 transferred blastocysts and morulae were classified into eight morphologic categories. The B1 category constituted the optimal blastocysts. The other categories were characterized by different deviations from optimal blastocysts: cytoplasmic fragments and necrosis in TE (B2), unexpanded blastocoele (B3), non-compact or small ICM (B4), fragments in TE and ICM (B5), up to 20% excluded blastomeres (B6), necrotic TE and ICM (B7), and more than 20% excluded cells from blastocysts (B8). The live birth rate was calculated from blastocysts with known outcome after transfer (88.9% transferred blastocysts). The birth rate declined from B1 to B8 by the same order and was: 45.2, 32.8, 26.9, 23, 17.7, 16.7, 7.7 and 1.2% respectively. Normal ICM was recognized as the most important parameter for implantation. There was a strong relation between such ordered morphology categories and implantation capacity (P < 0.0001). Such a grading system is helpful in selecting the best of all available day-5 embryos for transfer.