Evidence of impaired endometrial receptivity after ovarian stimulation for in vitro fertilization: a prospective randomized trial comparing fresh and frozen-thawed embryo transfer in normal responders

Objective: To compare success rates between fresh ETs after ovarian stimulation and frozen-thawed ETs (FET) after artificial endometrial preparation, to compare endometrial receptivity. Design: Randomized, controlled trial. Setting: Private fertility center. Patient(s): Therewere 53 patients completing fresh blastocyst transfer (fresh group) and 50 patients completing FET (cryopreservation group). All were first-time IVF patients aged <41 years, with cycle day 3 FSH <10 mIU/mL and 8-15 antral follicles. Intervention(s): Randomized to fresh or thawed ET. Main Outcome Measure(s): Clinical pregnancy rate per transfer. Result(s): The clinical pregnancy rate per transfer was 84.0% in the cryopreservation group and 54.7% in the fresh group. The implantation rates were 70.8% and 38.9%, respectively. The ongoing pregnancy rates per transfer (at 10 weeks' gestation) were 78.0% and 50.9%, respectively. The attributable risk percentage of implantation failure due to reduced endometrial receptivity in the fresh group was 64.7%. Conclusion(s): The clinical pregnancy rate per transfer was significantly greater in the cryopreservation group than in the fresh group. These results strongly suggest impaired endometrial receptivity in fresh ET cycles after ovarian stimulation, when compared with FET cycles with artificial endometrial preparation. Impaired endometrial receptivity apparently accounted for most implantation failures in the fresh group. ClinicalTrials.gov Identifier: NCT00963625. (Fertil Steril (R) 2011; 96: 344-8. (c) 2011 by American Society for Reproductive Medicine.)