Comparison of mechanical artificial shrinkage methods in mouse blastocyst vitrification.

PURPOSE OF INVESTIGATION: This study was designed to determine which mechanical artificial shrinkage (AS) method, conducted by puncture, pipetting, or aspiration, was effective in increasing the re-expansion rate of mouse blastocysts. MATERIALS AND METHODS: In each group, 30 mouse blastocysts were used. Before vitrification, the blastocoelic cavity was collapsed by puncture with a micro-needle, pipetting with a micro-glass pipette, and direct aspiration with an ICSI pipette. After thawing, the re-expansion rate of blastocysts was examined for each AS method. Re-expansion rate was checked at three, five, and seven hours after thawing. RESULTS: The number of re-expanded mouse blastocysts at five hours after thawing was 12 in the puncture with a micro-needle group, 11 in the pipetting with a micro-glass pipette group, and 24 in the direct aspiration with an ICSI pipette group. The cumulative number of re-expanded mouse blastocysts at seven hours after thawing was 20 in the puncture with a micro-needle group, 20 in the pipetting with a micro-glass pipette group, and 28 in the direct aspiration with an ICSI pipette group. There were statistically significant differences in the cumulative number of re-expanded mouse blastocysts between five and seven hours after thawing (p = 0.001 and 0.021, respectively). CONCLUSIONS: Direct aspiration with an ICSI pipette resulted in a higher re-expansion rate than the puncture and pipetting methods. It can be considered that the direct aspiration method is more convenient and simpler than the other two methods.