Slow freezing and vitrification of mouse morula and early blastocysts

Area of Science:

• Reproductive biology
• Embryology
• Cryobiology

Background:

• Embryo cryopreservation is crucial in assisted reproductive technologies.
• Expanded blastocyst stage freezing is common, but earlier stage freezing offers potential benefits.
• Optimizing cryopreservation protocols for earlier embryo stages is essential for clinical application.

Purpose of the Study:

• To compare the efficacy of slow freezing versus vitrification for mouse morula and early blastocysts.
• To evaluate survival, blastocyst development, and implantation rates using clinically applicable protocols.
• To assess the potential of vitrification as an alternative to expanded blastocyst freezing.

Main Methods:

• Mouse morula and early blastocysts underwent slow freezing/thawing or vitrification/warming.
• Assessed were survival, blastocyst development, cell number, and cell allocation.
• Implantation and fetal development were determined after transfer to pseudopregnant recipients.

Main Results:

• Vitrification yielded significantly higher survival and blastocyst development rates than slow freezing for both morula and early blastocysts.
• Slow-frozen early blastocysts showed reduced cell numbers; however, vitrified embryos and slow-frozen morulae had comparable cell numbers to controls.
• Implantation rates were similar across cryopreservation methods, but placentas from slow-frozen early blastocysts were lighter.

Conclusions:

• Vitrification significantly enhances morula and early blastocyst survival and development compared to slow freezing.
• A closed, DMSO-free vitrification protocol was validated, showing promise for clinical use.
• This protocol could serve as a viable alternative to expanded blastocyst stage freezing in clinical settings.