This study was designed to evaluate the applicability ojthe pronuclear scoring system (Z-score) alone. or in combination with maternal variables to predict embryo grade determined on day 3 Jrom a large number oj embryos derived from patients undergoing treatment with NF and!or rcs!. The study included 92 couples assigned to undergo NF or resr Jor primary (66.3%) or secondary (33_ 7%) inJertility due to male Jactor in 30.4%. Jemale Jactor in 55.5% or unexplained inJertility in 14.1%. A total oj 500 zygotes oj a total oj 611 oocytes were evaluatedJor Z-scoring at 16-18 hours qfter JertiliZation and Jollowed Jor embryo grading on day 3 Jor evaluation ojstatistical relation between both and to determine the specificity and sensitivity ojZ-score and certain maternal variables in such relation. There were 265, 172, 43 and 20 zygote~ oJZ-1, Z-2, Z-3 and Z-4 scores. Using regression analysis, Z-scoring showed highly significant (P=O.OOO) difference in comparison to other variables in prediction oj the embryo grade on day 3 and showed high specificity as determined using . the receiver operating characteristic (ROC) curve analysis. It could be concluded that the pronuclear scoring system oj zygotes is a specific predictor oj the embryo grade on day 3 after NF and!or ICSI and signifkantly aidJor selection oJtop quality embryo.