To determine the impact of the peak E2 level and its midluteal decline on IVF- ET outcome in a group of normal- and highresponding patients. Retrospective analysis of IVF- ET data. Tertiary- care, university- affiliated teaching hospital. A total of 100 patients aged ≤ 38 years and receiving up to three embryos per transfer who underwent a similar standard controlled ovarian hyperstimulation for IVF- ET. Morning blood was collected on days 0 (hCG day), + 9, and + 14. Treatment cycle hormonal characteristics and percent midluteal E2 decline in conception and nonconception cycles. Among all cycles, a mean decline of 95.0% in serum E2 was observed at the midluteal phase. No significant differences were found in various parameters comparing conception with nonconception cycles. Occurrence of conception did not correlate with the absolute E2 level or with percent E2 decline in good and high responders. Early spontaneous abortion occurred more frequently in high responders with >98% E2 decline; however, the difference did not reach statistical significance. Multifactorial analysis refutes the negative role of supraphysiologic levels of E2 on the day of hCG administration or its dramatic decline at the midluteal phase on the success rate after embryo transfer. A possibly increased rate of early spontaneous abortion in the high- response group warrants further verification. To determine the impact of the peak E2 level and its midluteal decline on IVF-ET outcome in a group of normal- and highresponding patients. Retrospective analysis of IVF- ET data. Tertiary- care, university- affiliated teaching hospital. A total of 100 Patients aged ≤ 38 years and receiving up to three embryos per transfer who underwent a similar standard controlled ovarian hyperstimulation for IVF-ET. Morning blood was collected on days 0 (hCG day), +9, and + 14. Treatment cycle hormonal characteristics and Percent midluteal E2 decline in conception and nonconception cycles. Among all cycles, a mean decline of 95.0% in serum E2 was observed at the midluteal phase. No significant differences found found in various parameters comparing conception with nonconception cycles. Occurrence of conception did not correlate with the absolute E2 level or with percent E2 decline in good and high responders. Early spontaneous abortion occurred more frequently in high responders with> 98% E2 dec line; however, the difference did not reach statistical significance. Multifactorial analysis refutes the negative role of supraphysiologic levels of E2 on the day of hCG administration or its dramatic decline at the midluteal phase on the success rate after embryo transfer. early spontaneous abortion in the high response group warrants further verification.