Purpose: To determine if the change in serum estradiol (E2) from the day of human chorionic gonadotropin (hCG) injection to the day after predicts pregnancy and implantation rates following in vitro fertilization-embryo transfer (IVF-ET) in less than average responders. Methods: A retrospective cohort analysis was performed in women with less than average follicular response as defined by a peak serum E2 on the day of hCG of < 1500 pg/ml despite a maximum stimulation gonadotropin protocol. Pregnancy and implantation rates were compared in five groups based on standard deviation (SD) below or above the mean. Results: No differences were found in outcome in any groups including those that were 1-2 SD below the mean or within 1 SD below the mean or up to 2 SD above the mean. The group that was 2 SD above the mean seemingly had higher pregnancy and implantation rates but there were insufficient numbers to allow statistical comparisons. There did not appear to be any confounding variables among these groups. Conclusions: A drop in serum E2 in a group of women that were less than average responders was not associated with a lower chance of conception following IVF-ET.