Comparative Outcomes of Day 3 and Day 5 Frozen-Thawed Embryo Transfers: A Retrospective Clinical Study.

Aim: This study aimed to compare the clinical pregnancy outcomes of Day 3 (cleavage-stage) and Day 5 (blastocyst) frozen-thawed embryo transfers in assisted reproductive technology (ART) cycles. Methods: A retrospective analysis was conducted on 6455 patients who underwent frozen-thawed embryo transfer (FET) between 1 April 2010 and 1 April 2023, at SBÜ Etlik Zübeyde Hanım Women's Health Training and Research Hospital. Patients were categorized based on embryo transfer type, and clinical outcomes were compared using statistical analyses. Results: Pregnancy rates were significantly higher in the blastocyst transfer group (p = 0.031). The cleavage-stage group had a higher number of embryo transfers (p < 0.001), likely due to lower implantation potential per embryo. Patients with diminished ovarian reserve had lower embryo freezing rates (p < 0.001). Blastocyst-stage transfers showed better synchronization with endometrial receptivity but carried a risk of embryo attrition. Conclusions: Blastocyst transfer is associated with higher pregnancy rates and should be preferred when viable embryos are available. However, cleavage-stage transfer remains an alternative for patients with poor embryo development. An individualized approach is essential for optimizing ART outcomes.