Limitations and Benefits of Morphologic Embryo Assessment Strategies: How Far Can Morphological Assessment Go in the Identification of Viable Embryos?

Abstract

Morphological assessment has been the primary tool of the embryologist for selecting which embryo(s) to replace. Since the early years of in vitro fertilization (IVF), it was noted that embryos cleaving faster and those of better morphological appearance were more likely to lead to a pregnancy. Indeed, Edwards and colleagues noted only a few years after the birth of Louise Brown “that cleavage rates on a certain day and overall embryo morphology were valuable in choosing which embryo to transfer.” In 1986 one of the initial large studies (N = 1,539 embryos) examining the utility of embryo morphology was published by Cummins et al. It was reported that embryo quality scores were valuable in predicting success. Indeed Cummins et al. calculated an embryo development rating based on the ratio between the time at which embryos were observed at a particular stage after insemination and the time at which they would be expected to reach that stage of a hypothetical “ideal” growth rate with a cell cycle length of 11.9 h. Using this scoring system, “normally” growing embryos scored 100; however, the scoring system appears to have never been assessed prospectively.