Estradiol, as an important hormone in follicular development and endometrial receptivity, is closely related to clinical outcomes of fresh in vitro fertilization embryo transfer (IVF-ET) cycles. The aim of this retrospective study was to evaluate the association between elevated serum estradiol (E2) levels on the day of human chorionic gonadotrophin (hCG) administration and IVF-ET pregnancy and birth outcomes. A total of 1771 infertile patients with their first fresh IVF-ET cycles were analyzed retrospectively between January 2011 and January 2016 in Peking University First Hospital. Patients were categorized by serum E2 levels on the day of hCG administration into six groups: group 1 (serum E2 levels ≤ 1000 pg/mL, n = 205), group 2 (serum E2 levels 1001-2000 pg/mL, n = 457), group 3 (serum E2 levels 2001-3000 pg/mL, n = 425), group 4 (serum E2 levels 3001-4000 pg/mL, n = 310), group 5 (serum E2 levels 4001-5000 pg/mL, n = 237), and group 6 (serum E2 levels > 5000 pg/mL, n = 137). The retrieved oocyte and MII oocyte numbers and implantation and clinical pregnancy rates of the groups were compared as the first objective of the study. For the 360 women with singleton births among all patients, the area under the corresponding receiver operating characteristic curve (ROC curve) was calculated to assess the predictive value of the E2 change for the probability of low birth weight (LBW) infants as the second objective. The retrieved oocyte and MII oocyte numbers and implantation and clinical pregnancy rates gradually increased from groups 1 to 5 but decreased in group 6. The parameters of group 1 were statistically worse than those of the other groups, from group 2 to group 6 (the number of retrieved oocytes, t = 13.096, t = 23.307, t = 23.086, t = 26.376, t = 19.636, P < 0.003; the number of retrieved MII oocytes, t = 10.856, t = 20.868, t = 21.874, t = 23.374, t = 19.092, P < 0.003; the implantation rate, χ = 12.179, χ = 22.239, χ = 23.993, χ = 23.344, χ = 16.758, P < 0.003; the clinical pregnancy rate, χ = 16.415, χ = 28.074, χ = 35.387, χ = 37.025, χ = 24.590, P < 0.003). ROC analysis revealed that when a serum peak E2 of 3148 pg/mL was used to predict LBW. The results indicate that serum E2 levels have a concentration-dependent effect on clinical outcomes. The optimal range of the E2 level during a fresh IVF-ET cycle is 1000 to 3148 pg/mL.