<p>Background: The aim of this study was to assess the impact of total serum E2 on the day of human chronic gonadotropin (hCG) administration and the serum E2 per oocyte ratio on the outcomes of assisted reproductive technology (ART) cycles.<br /> Methods: A total of 205 women were categorized into 3 groups according to the serum E2 levels: 1: &le;1500 <em>pg/ml</em>; 2: 1500-3000 <em>pg/m</em>l; 3: &gt;3000 <em>pg/ml</em>. Another categorization included 3 groups according to E2/oocyte ratio: A: &le;150 <em>pg/ml</em> per oocyte; B: 150-200 <em>pg/ml </em>per oocyte; and C: &gt;200 <em>pg/ml</em> per oocyte. The outcome compared between groups included laboratory and clinical characteristics. One-way analysis of variance (ANOVA), chi-square and Kruskal-Wallis, and multiple logistic regression model were performed, and appropriate differences were considered significant at p&lt;0.05.<br /> Results: There was a significant difference between the groups based on the E2 levels with respect to laboratory parameters. In group C, the rates of chemical pregnancy (54.1%), clinical pregnancy (50%) and live birth (45.8%) were significantly higher, when compared to other groups. Moreover, according to E2/oocyte ratio, the rate of live birth was higher in group C compared with group A (18.3%, p=0.04), and group C (29.7%, p&lt;0.0001). Logistic regression showed the number of good quality embryos was a positive predictor for live birth (odds ratio=2.03, 95% CI=1-4.1), but the level of E2 on day of HCG was a negative predictor (odds ratio=0.99, 95% CI=0.99-1).<br /> Conclusion: Supraphysiological levels of E2 had no adverse effects on the quality of the embryos in IVF cycles, but may have adverse effect on live birth in fresh transfer. Also, it is confirmed that both the pregnancy and live birth rates were elevated with E2/oocyte ratio &ge;200 <em>pg/ml</em>.</p>