Objective

To investigate developing late morulas that frozen at day5 and the factor of associated with late morulas. DESIGN: Retrospective study.

Materials and Methods

We investigated late morulas which were frozen at day5 in our clinic from January 2010 to June 2014. All morulas were cultured for 20-26 hours after thawing. These embryos were divided two groups according to their formed blastocele and reached blastocysts (Formed group, n=94) or unformed blastocele (Unformed group, n=30). Furthermore, each groups were compared by female age, IVF number, compaction grade (grade1-3), fragmentation rate (%), blastomere number at day3 and extent of forming compaction at day4 (unformed compaction; 0, partial compaction; 0.5, full compaction; 1).

Results

There were no significant differences between Formed group and Unformed group with female age (36.5 versus 37.9, P=0.08), IVF number (3.07versus 3.77, P=0.11), compaction grade (1.95versus 1.73, P=0.09), fragmentation rate (9.57versus 8.00, P=0.27) and blastomere number at day3 (7.72versus 8.07, P=0.39). However, there was a significant difference in morphology at day4, the rate of compaction at day4 was higher in Unformed group (0.43 versus 0.68, P=0.003).

Conclusions

When late morulas frozen at day5 had already widely formed compaction at day4, they were high possibility of development arrest after thawing.