The correlation between morphology and implantation of euploid human blastocysts.

Research Question: Does the composite morphology score or a particular developmental component (expansion stage, inner cell mass [ICM] or trophectoderm [TE]) of euploid blastocysts undergoing single frozen embryo transfer (FET) impact ongoing pregnancy/live birth (OP/LB) rates?

Design: Retrospective cohort study including a total of 2236 embryos from 1629 patients who underwent single euploid FET between 2012 and 2017.

Results: Embryos with an ICM grade of A compared with C had a higher OP/LB rate (55.6% versus 32.3%, P < 0.001). Blastocysts with a TE grade of A or B compared with C had a higher likelihood of OP/LB (A versus C: odds ratio [OR] 1.6, 99% confidence interval [CI] 1.1-2.3, B versus C: OR 1.5, 99% CI 1.1-2.1), and blastocysts with a developmental stage of 4 or 5 compared with 6 had higher odds of OP/LB (4 versus 6: OR 1.6, 99% CI 1.2-2.2, 5 versus 6: OR 1.6, 99% CI 1.2-2.3).

Conclusions: Among euploid embryos, ICM morphology is the best predictor of sustained implantation; however, a composite score may provide additional guidance. While there is a known benefit in genomic screening prior to embryo selection, morphology provides individualized, prognostic information about implantation potential.