One-step warming of human blastocysts under different thawing solution volumes, processing times and osmotic...

What is the optimal equilibration time and liquid volume of the thawing solution for blastocyst one-step warming, and do different thawing solutions and those with differing osmolarities affect survival and recovery?

Survival, recovery and recovery times of blastocysts were investigated after one-step warming under various conditions. Study 1: blastocysts were randomly allocated to four groups (63 blastocysts/group) based on thawing solution volume and exposure time (group 1: 1000 µl/60 s; group 2: 1000 µl/30 s; group 3: 500 µl/60 s; group 4: 500 µl/30 s); study 2: comparison of thawing solutions from two manufacturers (Irvine Scientific and Kitazato) (115 blastocysts/group); study 3: evaluation of thawing solutions with different osmolarities: Vit Kit-Warm NX Thawing Solution (1641 mOsm), Vit Kit-Warm NX Dilution Solution (896 mOsm), Continuous Single Culture-NX (264 mOsm), and Global Total (266 mOsm) (68 blastocysts/group).

No difference in survival, recovery (95.2-100%) rates and recovery times were observed among groups in study 1. In study 2, no difference in survival rate and recovery time was observed between groups; however, Irvine Scientific (24/24 [100%]) recovered significantly more low-grade blastocysts than Kitazato (9/12 [75.0%]). In study 3, no difference in survival (95.5-100%) and recovery (92.6-100%) rates was observed. Regarding recovery time, dilution solution was significantly faster than Global Total (P < 0.05).

One-step warming was effective under various osmotic pressure conditions and offered a simplified approach to embryo culture. The study was small and limited by the single-centre design. The method should be further investigated under optimal conditions.