摘要Aims:This research aims to explore the factors related to early spontaneous miscarriage after in vitro fertilization and embryo transfer(IVF-ET)pregnancy,and to provide guidance for improving pregnancy outcomes.Methods:We retrospectively analyzed the data for clinical pregnant women(2591 cycles)undergoing IVF-ET at the reproductive center of Peking University People's Hospital from January 2017 to December 2018;This included 544 ET cycles and 2047 frozen embryo transfer cycles.The analysis of factors associated with early miscarriage in the overall population of IVF/intracytoplasmic sperm injection(ICSI)pregnancies(including fresh and thawing cycles)was performed.Results:The risk of early miscarriage in the 35-39 age group was 1.35 times higher than that in the＜35 age group(OR=1.35[1.05,1.73],p=0.02).In addition,the risk of early miscarriage was 3.88 times higher in the group≥40 years old than in the group＜35 years old(OR=3.88[2.68,5.62],p＜0.001).Endometrial thickness also affected the miscarriage rate;the early miscarriage risk with endometrial thickness ≥8.5 mm was 0.78 times than that of the＜8.5 mm group(OR=0.78[0.62,0.98],p=0.03).The early miscarriage rate during frozen embryo transfer was 1.48 times higher than that during fresh embryo transfer(OR=1.48[1.08,2.02],p=0.01),while in the fresh cycle,the risk of early miscarriage with high-quality embryos was 0.5 times lower than that with non-high quality embryos(OR=0.5[0.27,0.9],p=0.02).In the frozen cycle,the risk of early miscarriage in natural cycle transplantation was 0.73 times that in hormone replacement treatment(HRT)cycle transplantation(OR=0.73[0.54,0.97],p=0.03).Conclusions:Advanced age is an independent risk factor for early miscarriage,while endometrial thickness at the date of transplantation is an independent protective factor.The risk of early miscarriage in fresh-cycle trans-planted embryos is significantly lower than that in frozen embryos,and the number of high-quality embryos in the fresh cycle lowers the miscarriage rate significantly.Natural cycle transplantation has a lower rate of early miscarriage than hormone replacement therapy.