Comparison of natural and artificial cycles in frozen-thawed embryo transfer: A retrospective analysis of 1696 cycles

This study aimed to compare the pregnancy outcomes of natural cycles (NC) and artificial cycles (AC) in patients undergoing endometrial preparation for frozen-thawed embryo transfer (FET). This retrospective cohort study was conducted in a private infertility clinic between September 2016 and January 2021 and reviewed 1696 FET cycles. Among these FET cycles, endometrial preparation protocols that are performed as the NC (group 1) and AC (group 2) were analyzed. Outcome measures were live birth rates (LBR), clinical pregnancy rates (CPR), implantation rates (IR), and miscarriage rates (MR). The mean serum estradiol level before progesterone supplementation was significantly higher in group 2, whereas endometrial thickness before progesterone supplementation was higher in group 1 (p0.05). Additionally, CPR and LBR were similar in groups 1 (39.2% and 32.8%) and 2 (37.3% and 28.5%) (p=0.517, p=0.134, respectively). Multivariate logistic regression analyses revealed that female age at embryo freezing time and the number of transferred embryos were predictable variables of live birth [odds ratio (OR): 0.970, confidence interval (CI): 0.948-0.991, p