Equivalent blastocyst rates after freezing murine embryos in Cryo Bio System high security or standard instruments-medicine-veterinarian straws

Abstract

Objective To validate the Cryo Bio System (CBS) straw in our current cryopreservation system before using it in clinical practice. Design A prospective comparison of blastocyst development rates in 278 murine embryos after refreezing and thawing at the two-cell stage against the standard Instruments-Medicine-Veterinarian (IMV) straw used in our cryopreservation program. Setting Private IVF laboratory. Patient(s) No human subjects or material was used in this study. Intervention(s) Frozen two-cell murine embryos were thawed and randomized into three treatments [1] refreezing in the CBS straws, [2] refreezing in IMV 0.25-mL straws, and [3] control embryos remaining in culture without refreezing. Embryos were refrozen using identical cryoprotectants and identical programmed controlled-rate freezers. After cryopreservation, straws were held in liquid nitrogen for a brief period before thawing and continued culture. Main outcome measure(s) Postthaw murine blastocyst development rate. Result(s) When the manufacturer’s filling and loading protocol was used for the CBS straw there was no significant difference in the blastocyst development rate between CBS (75.0%) and IMV (76.4%) straws. Conclusion(s) The CBS straw may be a viable and potentially safer alternative for cryopreservation of human embryos, particularly for patients with known infections.