Selection of high-quality and viable blastocysts based on timing of morula compaction and blastocyst formation.

Purpose: The time-lapse system is a device that allows continuous monitoring without removing embryos from the incubator. Using a time-lapse system, we retrospectively investigated cleavage speed time points as potential indicators for selecting high-quality viable blastocysts.

Methods: This study included 963 zygotes of two pronuclei retrieved from 196 patients between January 2015 and December 2016. All embryos in culture were monitored by time-lapse after intracytoplasmic sperm injection. Of 492 blastocysts developed in vitro, 128 vitrified-warmed single blastocyst transfers were classified into pregnancy and non-pregnancy groups, and the parameters were compared.

Results: In the pregnancy group, timing of both morula compaction and regular blastocyst formation was significantly faster than in the non-pregnancy group. Furthermore, the optimal cutoff values for compacted morula (94.9 hours) and regular blastocyst (113.9 hours) were determined using the receiver operator characteristic curve analysis. Embryos that formed compacted morulae within 94.9 hours and developed into regular blastocysts within 113.9 hours were associated with a significantly higher pregnancy rate than those that did not (44.4% vs 16.0%).

Conclusion: The timing of morula compaction and regular blastocyst formation is important as an indicator of high-quality blastocysts to increase odds for pregnancy after embryo transfer.