Effect Of Frozen Embryo Transfer Timing Interval After Oocyte Retrieval On Pregnancy Outcome In Freeze-all Cycles

Background:Some studies demonstrated a negative effect of controlled hyperstimulation(COH)on endometrial receptivity.In consideration of the effect of COH on endometrium,frozen embryo transfer is generally postponed one menstrual cycle after oocyte retrieval.However,studies have found that there is no significant difference in clinical pregnancy rate between immediate transfer and delayed transfer.If the frozen embryo transfer is delayed without basis,it will increase the anxiety and pressure of infertile couples.In recent years,many researchers have devoted themselves to exploring the optimal timing of frozen embryo transfer,but due to the limitation of different research populations and research programs,the results lack of consistency.Objective:In this study,patients choosing freeze-all strategy were divided into two groups according to the time interval from oocyte retrieval to embryo transfer,and the effects of transfer at different times on pregnancy outcome were compared and analyzed.To explore the most appropriate transfer time,and provide reference for clinicians to make decisions,and try to relieve the psychological pressure of patients.Methods:This was a retrospective cohort study included patients who underwent an in vitro fertilization(IVF)/intracytoplasmic sperm injection(ICSI)in freeze-all cycle between January 2017 and October 2019 in Center for Reproductive Medicine Shandong University.A total of 4360 patients met the inclusion criteria and were divided into two groups according to the interval from oocyte retrieval to frozen embryo transfer time:Group 1 with an interval ≤45 days,group 2 with an interval>45 days.Population and subgroup analysis the differences of biochemical pregnancy rate,biochemical pregnancy loss rate,clinical pregnancy rate,early miscarriage rate and live birth rate between the two groups,to explore the most suitable transfer time of frozen embryo.Results:There was no significant difference in biochemical pregnancy rate,biochemical pregnancy loss rate,clinical pregnancy rate,early miscarriage rate and live birth rate between the immediate transfer group and the delayed transfer group.Subsequently,the endometrial preparation,the incidence of PCOS,the reasons for the cancel of fresh embryo transfer,COH type and the number of oocyte retrieval were analyzed.We found that the biochemical pregnancy loss rate(29.0%vs.10.7%,p=0.005)and early miscarriage rate(27.3%vs.10.8%,p=0.027)in the immediate transfer group were significantly higher than those in the delayed transfer group,and the clinical pregnancy rate(44.9%vs.64.6%,p=0.006)and live birth rate(32.7%vs.55.4%,p=0.002)were significantly lower than those in the delayed transfer group,with statistical differences.In non-PCOS patients,the live birth rate was significantly lower in the immediate transfer group(38.4%vs.51.1%,p=0.033)than in the delayed transfer group.In patients who canceled fresh embryo transfer due to increased serum progesterone on HCG day,biochemical pregnancy rate(30%vs.69.6%,p=0.010),clinical pregnancy rate(30.0%vs.62.1%,p=0.044)and live birth rate(10%vs.52.8%,p=0.009)were all significantly decreased in the immediate transfer group.According to COH type and number of oocyte retrieval by subgroup analysis,there was no statistical difference in pregnancy outcome between the two groups.Conclusion:The time interval of frozen embryo transfer after ovulation had no effect on pregnancy outcome.However,when choosing natural cycles,or in non-PCOS patients and patients who have canceled fresh embryo transfer due to high HCG day of progesterone,delayed transfer should be properly considered.In clinical application,economic factors,patient requirements,medical conditions and other factors should be considered.