Embryo Cleavage Itself is a Strong Predictor of Embryo Quality and in Human IVF

Abstract

Selecting the right embryos for transfer in assisted reproductive technology (ART) seems to be very important in terms of outcome; although this selection is not easy to do. Amongst other strategies, many embryo scores have been proposed for embryo selection in order to achieve a higher implantation and pregnancy rate, while minimizing the risk of multiple pregnancy. However, there is no consensus about which the best parameter is. Generally, scores include morphological criteria such as: cell fragmentation, blastomere and embryo symmetry, and the use of complex formulas to make an appropriate score. Many authors suggest that the fastest cleaving embryos are considered to have the best developmental potential acting as an individual prognostic factor. The objective of this study was to analyze whether the cleavage rate is a better predictor of implantation and pregnancy rate than the embryo morphological score. None A cohort of 769 cycles of women undergoing their first fresh embryo transfer (ET) was prospectively evaluated. Inclusion criteria were: age 18 to 39 years, basal FSH levels ≤ 12 IU/L, and 3 or 4 embryos transferred to the uterus on day 3. Oocyte donation cycles were excluded. Embryos were scored considering: cleavage rate, and embryo morphology according to cell fragmentation (%), and embryo and blastomere symmetry (embryos were scored 1 to 4, being 4 the best). Global embryo score (GES) was calculated by adding the score of every single embryo transferred. Best quality embryos added a GES of 12 points or above. Cleavage rate was calculated by adding the number of blastomeres of all the embryos considering a high cleavage rate when it was equal to or above 24 points. Statistical analysis was made using chi2 test for proportions, and t-test for continuous variables. Mean age of the study group was 33.6 ± 3.6 years, and ages between pregnant and non pregnant patients was comparable.Clinical pregnancy rate was 37.1 %. All pregnancy cycles had a GES of 9.5 ± 3.5 and a cleavage rate of 19.1 ± 7.5. Women who got pregnant had a GES 2 points higher and a cleavage rate 4 points higher than cycles without pregnancy (p<0.001).In terms of pregnancy achievement potential, good quality embryos had a sensitivity of 23.2%, with a specificity of 84.7%. When only cleavage rate was considered; 31.2% of women who got pregnant had high cleavage rates, while 82.8% of those who did not get pregnant had low cleavage rates (p<0.05) Although no good accurate pregnancy prognosis scores have been developed, many variables are known to be related with ART outcome. Whenever variables are simpler, its interpretation and use are easier. In this study, cleavage rate alone showed not only to be at least as specific as the morphological score requiring three components, but it was also more sensitive. We consider that this is not a minor finding when analysing which embryo is to be transferred to maximize results at low risks; and for research when we wonder which variables have to be considered to make a more accurate prognosis.