P-190 Osmolarity-dependent effects of one-step thawing of human blastocysts

Abstract Study question We investigated the effects of different thawing solution (TS) volumes, treatment times, and osmotic pressures on survival and recovery rates after thawing of blastocysts. Summary answer In one-step thawing, differences in TS volume, treatment time, and osmotic pressure had no effect on the survival and recovery rates after thawing of blastocysts. What is known already The usefulness of this one-step method has been reported previously. Here, we investigated the effects of TS volume, processing time, and osmotic pressure on one-step thawing and determined the optimal thawing conditions. Study design, size, duration This study included blastocysts that were discarded at our hospital. Cryopreservation and thawing of the blastocysts was performed by established methods using a CryoTip® (closed-system vitrification method). The blastocysts were considered to have survived if most of the cells had not degenerated and were alive. Blastocyst recovery was defined as the number of viable cells after thawing and the confirmation of a blastocoel after recovery culture (maximum of 10 h). Participants/materials, setting, methods In study I, one-step thawing was performed using Irvine Scientific Thawing solution (TS; 1,641 mOsm/kg H2O) in four groups. Survival and recovery rates (freezing day; Day 5 or 6), and blastocyst grade (good blastocysts or other blastocysts) were investigated. In study II (conditions; 1,000µL-60s), the survival and recovery rates and blastocyst grade after one-step thawing in TS and CSC-NX (264 mOsm/kg H2O) were investigated. Main results and the role of chance In Study I, blastocyst survival was confirmed in the 1,000µL-60s, 1,000µ-30s, 500µL-60s, and 500µL-30s groups (100% survival). There were several blastocysts that did not recover in the 500µL-30s group (recovery rate 94.4%); however, recovery of all blastocysts was confirmed in the other groups. In Study II, all the blastocysts were viable. The recovery rate was high (94.4–96.4%), although several blastocysts did not recover. Limitations, reasons for caution This was a single-facility study. Wider implications of the findings One-step thawing is considered effective because it shortens embryo manipulation time and reduces laboratory workload. The survival and recovery rates were good, although the volume of TS and treatment time were halved. One-step thawing was effective for CSC-NX, which has an osmolality six times lower than that of TS. Trial registration number No