Embryo classification method based in time-lapse analysis is associated with blastocyst quality

We aimed to discover if there is a correlation between a proposed embryo classification based on timing of cells division and blastocyst quality depending on morphokinetic parameters and its relation with implantation potential. Retrospective cohort study. We examined 872 embryos form 127 couples undergoing oocyte donation. In order to look for potential embryo markers predicting blastocyst development, we evaluated the percentage of optimal blastocysts based in the morphology of inner cell mass and trophoectoderm with cleavage divisional stage previously proposed. To evaluate embryo quality based in morphokinetics, the proportion of optimal embryos was determined from our previous observations, identifying embryos in a best time range with a higher implantation potential. The proposed optimal timings were as follows: t2: 24.3-27.9 h; t3: 35.4-40.3 h; t5: 48.8-56.6 h; s2:<0.76 h; cc2:<11.9 h. We applied a Chi-squared for comparison of percentages with P<0.05 considered to be statistically significant. The rate of embryos developing into blastocysts was higher for all cleavages times assessed, reaching statistical significance for t3, t5, cc2 and s2 and a similar trend was found for good-quality blastocysts with good morphology. The rate of blastocysts inside/outside the defined optimal ranges was: t2 61.3% vs 60%, P=0.740; t3 66.9% vs 56%, P=0.007; t5 72.8% vs 50.2%, P=0.000; cc2 67.5% vs 55.7%, P=0.003; and s2 71.3% vs 60.6%, P=0.018. According good-quality blastocysts, the data were as follows: t2 51.9% vs 51.8%, P=0.980; t3 56.5% vs 46.5, P=0.09; t5 56.2% vs 42.7%, P=0.028; cc2 54.2% vs 49.6%, P=0.434; and s2 56.6% vs 44.6%, P=0.065. Our results show that a larger fraction of the embryos whose cleavages took place within the proposed optimal time interval for implantation reached the blastocysts stage and exhibited good morphologic characteristics. There is a clear correlation between blastocyst development and morphokinetics grading to determine implantation.