ABSTRACT
Morphological evaluation of embryonic developmental competence prior to transfer has for many years been one of the key challenges in assisted reproduction. Many studies have shown that morphological structures in the embryo can be used as biomarkers of embryonic quality1-4 and that embryo selection based on morphology assessment is important to improve implantation and pregnancy rates.3,5-7Most of the existing scoring systems are based on combinations of several morphological parameters such as cleavage stage, embryonic fragmentation, and blastomere uniformity.1,3,7,8 However, in recent years assessing embryo quality has generally moved from scoring the embryos using a single grade to registering individual parameters considered to be important markers of embryo quality. This means that the embryo selection procedure is based on a balanced compromise after assessment of individual parameters. This move towards assessment of individual parameters has underlined the need for more objective measurements and more precise definitions. One example is equal blastomere size. When are the blastomere unequally sized? Some consider even the slightest difference as unequal size, and others demand larger differences for a classification of unequal size. Other examples that require more precise definition include degree of fragmentation and the size cutoff limit between a small blastomere and a large fragment.
