Embryo morphology as a predictor of IVF success: an evaluation of the proposed UK ACE grading scheme for cleavage stage embryos.

This study aims to provide a first evaluation of the morphological embryo grading scheme proposed in the British Fertility Society and Association of Clinical Embryologist joint guidelines for elective single embryo transfer. Pregnancy data were obtained from a cohort of patients treated at St. Mary's Hospital in Manchester, UK, between April 2007 and July 2009. Embryo morphology was assessed on day 2 or 3 prior to transfer in terms of 3 parameters: cell number, fragmentation and evenness. Cell number was parameterised as a growth rate (doublings/day). An embryo-uterus model with adjustment for other prognostic factors was used to determine the role of the three components as predictors of pregnancy. Embryo growth rate (p < 0.001) and fragmentation (p = 0.004) were strong predictors of pregnancy and after including these, evenness did not improve the prediction significantly (p = 0.39). Normally growing embryos have a higher implantation rate than slow and fast-growing embryos. The grading scheme has proved to be feasible and robust in routine clinical practice. Based on this single-centre retrospective series we propose a selection algorithm for day 2/3 embryos based on fragmentation and growth rate. The 3 parameter grading scheme has the potential for further discrimination as larger datasets become available.