The purpose of this study was to investigate the relationship between cell blood count) CBC (at the time of ovum-pick-up and the pre-implantation development of embryos. This study was performed on blood samples from 40 Holstein heifers that were prepared for ovum pick up and the samples were examined using an autoanalyzer. Blood samples containing anticoagulants were sent to the laboratory for measurement of blood cells such as monocytes, lymphocytes, eosinophils, basophils, neutrophils, erythrocytes, as well as hemoglobin and platelets. Subsequently, heifers were divided into two groups based their rate of blastocyte formation as: 1) heifers with no blastocytes. and 2) heifers with blastocytes.Then, for better understanding and observation of the difference in blastocyte rate and the effect of blood parameters Heifers were divided into three groups: 1) heifers that did not produce blastocytes ؛2) heifers that had a blastocyte rate of 5 to 40%.and 3) heifers with a blastocyst rate greater than 40%. Obtained data were analyzed using the Statview, Fisher procedure (Post hoc). The results showed that the lymphocyte concentration in 40-80% blastocytes heifers was significantly higher than those who were not able to produce blastocytes and their values were) 5.81±0.09%) and (4/74 ± 0.32%), respectively. Also, monocyte percentage (r 2 = -0.41, P = 0.009) and eosinophil percentage (r 2 = -0.32, P = 0.041) were correlated with blastocyte production rate. But the percentages of , hemoglobin, total red blood cells , and white blood cells as well as basophil and neutrophil percentages , were not significantly different between heifers. Overall, the results of this study indicate that some of the reproductive factors,such as blastocyte production rate (embryo production at day 7) , can be predicted using data from CBC testing. This could help us to predict a successful in vitro fertilization and blastocyte formation , as well as to estimate fertility rate in dairy cows . Keywords : Blood cell count, Blastocyte, In vitro fertilization, Lymphocyte, Monocyte