Time to blastulation is superior to individual components of embryo grading for livebirth prediction

Abstract Objective To compare components of the embryo grading system with time for blastocyst formation (i.e. day of embryo transfer) for predicting livebirth rate in frozen embryo transfer cycles. Design Retrospective cohort study Setting University affiliated fertility clinic Patients 870 frozen embryos were transferred in a total of 509 women and 728 cycles at our institution from January 2015 to October 2018. Interventions None Main Outcome Measures Probability of livebirth per cycle Results In unadjusted analysis of embryo grading components, both inner cell mass (ICM) and trophectoderm grades demonstrated a correlation with livebirth rates (p = 0.01). However, this effect was lost in ICM subgroup analysis by day of embryo transfer and preserved only in declining trophectoderm grades of day 6 transfers. In adjusted analysis for prediction of livebirth, only day of transfer was significant. When assessing composite score by SART embryo grading, good embryos that blastulated on day 6 were significantly less likely than day 5 to result in livebirth (RR 0.70, CI 0.58-0.85). Finally, in a predictive model adjusted for all individual components of embryo grade, the day of blastulation is the only significant contributor. Conclusions Time to blastulation is superior to other individual components of embryonic grading for prediction of livebirth.