The Correlations between Blastocyst Morphological Scores and Mosaic Levels

Several studies have delineated the link between blastocyst morphology and chromosomal abnormalities. All of the morphological components of a blastocyst, that is, expansion degrees, inner cell mass grades, and trophectoderm grades, may individually correlate with the ploidy status, resulting in difficulties in ranking the embryos. Moreover, embryo grading variability may occur in previous studies due to multiple reasons, such as subjective judgments of individual embryologists, laboratory settings, and observation time windows. The advantage of time-lapse (TL) monitoring is objectively and accurately defined observation time after fertilization. This study hypothesized that blastocyst morphology observed at a definite time period by TL monitoring might be more precisely correlated with the mosaic level of a blastocyst. We therefore refined embryo assessments by using the definition based on TL monitoring and hr-NGS was applied to classify the mosaic level of a blastocyst. In addition, the effectiveness of a converted morphlogical scores in predicting ploidy was evaluated by considering the effects of potential confounding variables. The results showed that blastulation kinetics, cleavage dysmorphisms, and blastocyst morphology in TL monitoring had significant correlations with mosaic levels. Converting blastocyst morphological components into a numerical score can be a potent ranking tool for predicting embryo ploidy.