First Use of a Modified Specific Gravity Device to Determine the Viability and Development Potential of Human Cryopreserved Embryos

Objective: Embryo cryopreservation is currently the only effective means for long-term storage, transport, and genetic testing of human and animal embryos. It also allows significant flexibility in scheduling ART procedures in fertility clinics. However, cryopreservation can also lead to embryo damage, affecting embryo viability and health. Previous research from this lab has demonstrated that a Modified Specific Gravity Device (MSGD) can be used to determine viability status and to predict the future development of embryos in various animal species. The current study describes the first use of the MSGD to determine post-thaw viability and development potential of donated cryopreserved human blastocyst stage embryos. Materials and Methods: A series of 192 vitrified blastocyst stage embryos (both non-biopsied and biopsied) from 44 patients were donated for research. After some initial testing, it was determined that only non-biopsied embryos should be passed through the MSGD to determine their buoyancy and drop time. Therefore, only 21 straws containing 27 non-biopsied embryos were used in this study. Embryos were first thawed using standard clinical laboratory techniques. Once thawed, the diameter of the zona pellucida of each embryo was estimated by using a microscope lens micrometer, the re-expansion status of the embryos was noted, the embryo was then dropped through the MSGD and placed in culture for 3 hrs at 37？C. After 3 hrs, each step was repeated and then embryos were returned to culture for 24 hrs to determine hatching. Statistical analyses were made comparing embryos that expanded by 3 hrs and hatched by 24 hrs to their descent time through the MSGD. Results: To date, we have completed data collection for 27 embryos. It was observed that most embryos at the initial time point did not demonstrate any expansion, and no differences were seen in their initial drop times (P = 0.754). However, at 3 hrs in culture, re-expanded embryos dropped more slowly through MSGD than those that did not expand (P < 0.04). Embryos that hatched had faster drop rates at both the initial and 3 hr measurement (P < 0.001 and P < 0.05), most likely due to concentration differences between cellular constituents and the media environment. Conclusion: Differences seen continue to suggest that a simple test of buoyancy may allow the determination of embryo viability and development potential. Further study is needed with a much larger embryo population to confirm these observations.