Morphological analysis at compacting stage is a valuable prognostic tool for ICSI patients.

In terms of treatment outcome, little prognostic power is attributed to day-4 morphology. A day-4 score was applied to 56 patients separating non-compacting embryos from compacting (some areas of compaction) and fully compacted embryos. The latter were further subdivided according to the morphology of compaction. Grade C1 embryos represented optimal quality, while grades C2 (exclusion of fragments) and C3 (exclusion of blastomeres) were characterized by a loss of cytoplasm. Grade 4 embryos (C4) showed incomplete compaction with several blastomeres not yet incorporated into cell mass. Pooled embryos without compaction showed a reduced (P < 0.001) blastulation (28.8%) as compared with compacting embryos with the same cell number (68.8%), which, in turn, revealed lower (P < 0.05) rates of blastulation as compared with concepti that completed compaction process (84.6%). Among fully compacted embryos grade C1 had a better (P < 0.01) blastocyst formation rate (94.4%) as compared with grade C3 (68.2%). Grade C1 embryos showed significantly higher rates of top-quality blastocysts as compared with grade C2 (P < 0.05) and C3 (P < 0.01). Blastocysts deriving from grade C1/C4 embryos led to a higher pregnancy rate as compared with the C2/C3 counterparts (P < 0.05). This modified score allows for adequate prediction of both blastocyst formation/quality and pregnancy.