One-step warming technique for vitrified human blastocysts using commercially available thawing solutions

What are the re-expansion rates and clinical outcomes obtained when employing a one-step warming technique using three commercially available thawing solutions on vitrified blastocysts, and how do they compare with the standard multi-step warming technique?

This retrospective cohort study involved 1173 frozen embryo transfers (FET) in women aged <42 years between December 2022 and December 2024. The blastocysts were warmed following multi-step warming guidelines (with Reprolife solutions) or using one-step warming with 1 min of immersion in a thawing solution. Warmed blastocysts were cultured in a recovery medium for 2-3 h, and then transferred to the embryo transfer medium. Embryo transfer was performed after another 2 h. Survival, re-expansion and clinical outcomes were compared between 573 FET using one-step warming and 600 FET using multi-step warming, as well as between one-step warming using three different brands of thawing solution: Irvine (319 FET), Kitazato (128 FET) and Reprolife (126 FET).

The re-expansion rate of blastocysts after 4-5 h was significantly higher with one-step warming (92.4%) compared with multi-step warming (86.8%) (P = 0.0009). The clinical pregnancy rate was also significantly higher with one-step warming (69.3%) compared with multi-step warming (61.2%) (P = 0.0042), but the ongoing pregnancy rate did not differ significantly between one-step warming (53.9%) and multi-step warming (49.2%). No significant differences in re-expansion or clinical outcomes were detected between the three different brands of thawing solution used for one-step warming.

One-step warming results in better re-expansion and clinical outcomes than multi-step warming, and one-step warming is equally effective with the three commercially available brands of thawing solution tested.