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Abstract Background The landscape of assisted reproductive technology (ART) has seen a significant shift towards frozen-thawed embryo transfers (FET) over fresh transfers, driven by technological advancements and clinical considerations. This study aimed to compare live birth outcomes between primary FET and fresh transfers, focusing on cycles without preimplantation genetic testing (PGT), using United States national data from the SART CORS database spanning from 2014 to 2020. Methods We performed a retrospective cohort study of autologous first ART cycles without PGT comparing primary embryo transfer (frozen thaw vs. fresh) success rates from the 2014–2020 SARTCORS database. Live-birth rates (LBR) and cumulative live-birth rates (CLBR) were compared between first FET versus first fresh embryo transfer from an index retrieval. Multivariate logistic regression (MLR) determined association between live birth outcomes and method of transfer. In a subsequent sub-analysis, we compared these two embryo transfer methods among patients with either diminished ovarian reserve (DOR) or male factor infertility. Results 228,171 first ART cycles resulted in primary embryo transfer. 62,100 initial FETs and 166,071 fresh transfers were compared. Initial FETs demonstrated higher LBR and CLBR compared to fresh transfers (LBR 48.3% vs. 39.8%, p 42yo (aOR 2.63, p < 0.0001). Conclusions Overall LBR and CLBR were greater for first FET than fresh transfers with incremental increases in odds of live birth with advancing age, suggesting the presence of a more favorable age-related change in endometrial receptivity present in frozen-thawed cycles. For both DOR and MF cycles, LBR and CLBR after primary transfer were greater for first FET than fresh. However, this was particularly evident in older ages for DOR cycles. This suggests that supraphysiologic stimulation in older DOR cycles may be detrimental to endometrial receptivity, which is in part corrected for in FET cycles.
Wang et al. (Sat,) studied this question.