Pronuclear score improves prediction of implantation rate in ICSI cycles

Abstract

Background: In assisted reproduction technology embryo competence is routinely evaluated on morphological criteria but their efficacy remains relatively low. Additional information could be obtained by evaluation of pronuclear (PN) morphology. Up to now controversial results have been reported about prognostic value of PN score. One of the main limitation of literature data is the use of different methods of PN classification. To this regard, in 2011 the ESHRE and Alpha Scientists in Reproductive Medicine defined three PN categories to standardize the zygote assessment. In this study we evaluated whether the consensus ESHRE-Alpha system for the pronuclear scoring could be an useful additional criterion to improve prediction of embryo implantation potential.Methods: This is a retrospective, longitudinal cohort study. We included 3004 zygotes from 539 women who underwent ICSI treatment at our Center between January 2014 and June 2019. The pronuclear were categorized as score 1: symmetrical, 2: non-symmetrical, 3: abnormal. A subset of 110 zygotes did not cleaved. On day 2-3 1163 embryos were transferred, 232 arrested, and 9 were cryopreserved. Among the 1490 embryos cultured up to day 5-7, 516 became blastocysts: 123 were transferred on day 5 and 393 were cryopreserved. Relationship between pronuclear score and cleavage rate, quality of embryos, blastocyst development, and implantation rate was evaluated by chi-square test. Multivariate regression analyses corrected the results for putative confounders (age of patient; infertility cause; cleavage-stage embryo morphology grade; day of transfer). Results: There was not significant difference in patients’ age, cleavage rate and embryo morphology among the three pronuclear score groups. No reduction of blastulation rates was found in score 2-3 (34%) groups respect to score 1 (35%). The pronuclear score 1-embryos had a higher implantation rate respect to score 2-3-ones (15% and 9%, respectively, P=0.0121; OR 0.46; 95% CI 0.25-0.76, P=0.004). Consistently, the pronuclear score remained predictive of implantation in top quality embryos (OR 0.51; 95% CI 0.28-0.87, P= 0.01).Conclusions: The consensus pronuclear score may be routinely included among criteria for embryo evaluation to increase patient’s chance of becoming pregnant.