Which set of embryo variables is most predictive for live birth? A prospective study in 6252 single embryo transfers to construct an embryo score for the ranking and selection of embryos.

Study Question: Which embryo score variables are most powerful for predicting live birth after single embryo transfer (SET) at the early cleavage stage?

Summary Answer: This large prospective study of visual embryo scoring variables shows that blastomere number (BL), the proportion of mononucleated blastomeres (NU) and the degree of fragmentation (FR) have independent prognostic power to predict live birth.

What Is Known Already: Other studies suggest prognostic power, at least univariately and for implantation potential, for all five variables. A previous study from the same centre on double embryo transfers with implantation as the end-point resulted in the integrated morphology cleavage (IMC) score, which incorporates BL, NU and EQ.