Extending the culture of cleavage-stage embryos to the blastocyst stage after warming increases the chance of live birth: does it have a regenerative effect?

Purpose: We aimed to evaluate the effect of extending the culture of cleavage-stage embryos to the blastocyst stage in vitrified-warmed cycles on pregnancy outcomes.

Methods: This is a retrospectively designed pilot study of a single center. All patients who applied for freeze-all cycle procedures during in vitro fertilization treatment were included in the study. Patients were classified into three subgroups. The embryos obtained were frozen at the cleavage or blastocyst stage. After a warming process, the cleavage-stage embryos were divided into two subgroups: the first group of embryos was transferred (vitrification day 3-embryo transfer (ET) day 3 (D3T3)) on the warming day; for the second group, the embryo culture was extended to the blastocyst stage (vitrification day 3-ET day 5 (after the extension of the embryo culture to the blastocyst stage), (D3T5)). Frozen blastocyst-stage embryos were transferred after warming (vitrification day 5-ET day 5 (D5T5)). Hormone replacement treatment was the only endometrial preparation regimen given during the embryo transfer cycle. The main outcome of the study was live birth rates. The clinical pregnancy rate and positive pregnancy test rate were determined as the secondary outcomes of the study.

Results: The study included a total of 194 patients. The positive pregnancy test rates (PPR) and clinical pregnancy rates (CPR) of the D3T3, D3T5, and D5T5 groups were 14.0% and 59.2%; 43.8% and 9.3%; and 56.3% and 39.6%, respectively (p < 0.001 and p < 0.001). The live birth rates (LBR) of patients in the D3T3, D3T5, and D5T5 groups were 7.0%, 44.7%, and 27.1%, respectively (p < 0.001). In subgroup analysis of patients with a poor number of 2PN embryos (defined as having <  = 4 2PN embryos), the D3T5 group had significantly higher PPR (10.7%, 60.6%, 42.4%; p < 0.001), CPR (7.1%, 57.6%, 39.4%; p < 0.001), and LBR (3.6%, 39.4%, 21.2%; p: 0.001).

Conclusion: Extending the culture after warming to the blastocyst stage may be a better alternative than a cleavage-stage embryo transfer.