A comparison of the morphokinetic profiles of embryos developed from vitrified versus fresh oocytes

Research question: Do morphokinetic profiles and treatment outcomes differ between embryos developed from vitrified or fresh oocytes?Design: Retrospective multicentre analysis using data from eight CARE Fertility clinics across the UK between 2012 and 2019. Patients receiving treatment using embryos developed from vitrified oocytes (n = 118 women, n = 748 oocytes), providing 557 zygotes during this time period, were recruited and matched with patients undergoing treatment with embryos developed from fresh oocytes (n = 123 women, n = 1110 oocytes), providing 539 zygotes in the same time frame. Time-lapse microscopy was used to assess morphokinetic profiles, including early cleavage divisions (2-through to 8-cell), post-cleavage stages including time to start of compaction, time to morula, time to start of blastulation and time to full blastocyst. Duration of key stages such as the compaction stage were also calculated. Treatment outcomes were compared between the two groups (live birth rate, clinical pregnancy rate and implantation rate).Results: A significant delay of 2-3 h across all early cleavage divisions (2-through to 8-cell) and time to start of compaction occurred in the vitrified group versus fresh controls (all P < 0.01). The compaction stage was significantly shorter in vitrified oocytes (19.02 + 0.5 h) compared with fresh controls (22.45 + 0.6 h, P < 0.001). There was no difference in the time that fresh and vitrified embryos reached the blastocyst stage (108.03 + 0.7 versus 107.78 + 0.6 h). There was no significant difference in treatment outcomes between the two groups.Conclusion: Vitrification is a useful technique for extending female fertility with no effects on IVF treatment outcome.