Pregnancy Outcomes of Frozen-Thawed Blastocysts versus Blastocysts Derived from Frozen-Thawed Cleavage Embryos: A...

Limited data exist regarding the outcomes of frozen-thawed cleavage-stage embryos that undergo extended culture to reach the blastocyst stage. This study aimed to compare the pregnancy outcomes between two approaches: transferring blastocysts derived from frozen-thawed cleavage embryos (D3-5 group) and frozen-thawed blastocysts (D5 group).

This retrospective observational cohort analysis was conducted at Hung Vuong Hospital (CS/HV/24/23) from January 2022 to December 2023. The D3-5 group comprised 167 patients who underwent embryo transfer with frozen-thawed cleavage embryos, which were subsequently cultured for 2 days before being transferred as blastocysts. The D5 group included 342 patients who received frozen-thawed blastocysts. Positive human chorionic gonadotropin (hCG) rate, clinical pregnancy rate, ongoing pregnancy rate, live birth rate, pregnancy failure rate and cancellation rate were compared between the two groups.

In the D3-5 group, a significant proportion of cycles (65.3%) were cancelled, primarily due to the absence of developed blastocysts for transfer (85.3%), while the remaining 14.7% of cancellations were attributed to other reasons. Patients in the D3-5 group demonstrated comparable pregnancy outcomes to those in the D5 group: positive hCG rate (52 vs. 53%, P=0.898), clinical pregnancy rate (45 vs. 48%, P=0.785), ongoing pregnancy rate (34 vs. 33%, P=0.873), live birth rate (31 vs. 29%, P=0.839), and pregnancy failure rate (21 vs. 24%, P=0.656).

The strategy of culturing frozen-thawed cleavage embryos for two days and transferring them as blastocysts is not inferior to the transfer of frozen-thawed blastocysts. It increases workload for embryologists and poses a risk of cycle cancellation. We propose that the use of frozen-thawed blastocysts may be a more efficient and patient-friendly option.