The association between quality of supernumerary embryos in a cohort and implantation potential of the transferred blastocyst.

Purpose: Despite studies focused on the association between embryo morphology and implantation potential, it is unknown how the collective quality of the supernumerary embryos in a cohort is associated with the implantation rate (IR) of the transferred embryo. This study tested the hypothesis that a relationship exists between the quality of the supernumerary cohort and IR.

Methods: A retrospective cohort study of first fresh autologous IVF cycles from 05/2012 to 09/2016, with ≥ 3 blastocysts, resulting in a single blastocyst transfer (n = 819) was performed. Cohorts were grouped in two ways: by mean priority score (PS; 1 being best) of supernumerary embryos and by percent supernumerary embryos with low implantation potential. The relationship between cohort quality and IR was assessed using logistic regression.

Results: As mean cohort PS increased, IR of the transferred embryo decreased (test for linear trend, p = 0.05). When ≥ 75% of the supernumerary cohort was predicted to have low implantation potential, IR of the transferred embryo was significantly lower compared to when < 75% of the cohort was predicted to have low implantation potential (OR 0.71; 95% CI (0.53-0.94)). All associations were attenuated when adjusting for PS of the transferred embryo.

Conclusions: Our findings suggest that quality of supernumerary embryos is associated with IR of the transferred embryo, among patients with ≥ 3 blastocysts available on day 5. As cohort quality declines and the proportion of low implantation potential embryos increases, the IR of the transferred embryo declines. These associations are attenuated when controlling for quality of the transferred embryo, suggesting that the relationship between embryo cohort quality and implantation is not independent of the transferred embryo quality.