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STUDY QUESTION: Can a modified specific gravity technique be used to distinguish viable from nonviable embryos? SUMMARY ANSWER: Preliminary data suggests a modified specific gravity technique can be used to determine embryo viability and potential for future development. WHAT IS KNOWN ALREADY: Single embryo transfer (SET) is fast becoming the standard of practice. However, there is currently no reliable method to ensure development of the embryo transferred. STUDY DESIGN, SIZE, DURATION: A preliminary, animal-based in vitro study of specific gravity as a predictor of embryo development using a mouse model. PARTICIPANTS/MATERIALS, SETTING, METHODS: After a brief study to demonstrate embryo recovery, experiments were conducted to assess the ability of the specific gravity system (SGS) to distinguish between viable and nonviable embryos. In the first study, 1-cell mouse embryos were exposed to the SGS with or without previous exposure to an extreme heat source (608C); measurements were repeated daily for 5 days. In the second experiment, larger pools of 1-cell embryos were either placed directly in culture or passed through the SGS and then placed in culture and monitored for 4 days. MAIN RESULTS AND THE ROLE OF CHANCE: In the first experiment, viable embryos demonstrated a predictable pattern of descent time over the first 48 h of development (similar to previous experience with the SGS), while embryos that were heat killed demonstrated significantly altered drop patterns (P<0.001); first descending faster. In the second experiment, average descent times were different for embryos that stalled early versus those that developed to blastocyst (P<0.001). Interestingly, more embryos dropped through the SGS developed to blastocyst than the culture control (P<0.01). LIMITATIONS, REASONS FOR CAUTION: As this is a preliminary report of the SGS technology determining viability, a larger embryo population will be needed. Further, the current in vitro study will need to be followed by fecundity studies prior to application to a human population. wider implications of the findings: If proven, the SGS would provide a noninvasive means of assessing embryos prior to transfer after assisted reproductive technologies procedures, thereby improving fecundity and allowing more reliable SET. STUDY FUNDING/COMPETING INTEREST(S): The authors gratefully acknowledge the funding support of the U.S. Jersey Association, the Laura W. Bush Institute for Women's Health and a Howard Hughes Medical Institute grant through the Undergraduate Science Education Program to Texas Tech University. None of the authors have any conflict of interest regarding this work. TRIAL REGISTRATION NUMBER: none. [ABSTRACT FROM AUTHOR]

OBJECTIVE: Studies have suggested single embryo transfer (SET) could prevent risks from multiple gestations resulting from ART. However, embryos are currently selected by morphological appearance and developmental rate, which have been shown inadequate to ensure success after SET. Because multiple embryos are created during IVF, SET often leads to cryopreservation of super numeral embryos for later transfer attempts. However, cryopreservation has its own inherent risks to embryo viability. The objective of this study was to identify if embryo density can be used to detect cryodamage. DESIGN: Culture based study. MATERIALS AND METHODS: Previous research from this lab suggested embryo weight could detect cryodamage in sheep. To further examine this observation, mice embryos were cultured to blastocysts. Fresh blastocysts were analyzed using a modified specific gravity technique (MSGT). Blastocysts were then frozen using global® Blastocyst Fast Freeze® Kit. Embryos were stored in cryotanks for a minimum of two weeks. Embryos were thawed with global® Blastocyst Fast Freeze® Thawing Kit. Thawed blastocysts were then reevaluated using the MSGT. Blastocysts were cultured for 48 hours. Survival was determined by blastocysts hatching out of zona pellucida. RESULTS: Data from an earlier sheep study suggest a difference in the density of embryos in sheep that conceived verses those who did not (P < 0.046). Embryos with average to slow descent times (low density) blastocysts established more pregnancies that survived to term than faster descending blastocysts, which often did not establish pregnancy at all. Post-thaw mice embryo data supported sheep study with embryos with average to slow descent times hatching at a higher rate than embryos that descended rapidly thru the MSGT (P < 0.029). Mice embryos embryos that showed fewer differences, which had similar weights pre-freeze and post-thaw survived at a greater rate than embryos with large differences in weight (P < 0.016). CONCLUSION: Embryo density could suggest biochemical information that cannot be determined from morphological assessment. Cryodamage can be detected by variability of embryo density, possibly because damaged embryos have lost the ability to osmoregulate themselves due to membrane disruption, making them denser. Current studies are examining if MSGT can determine embryo sex due to weight differences in X and Y chromosomes. This data continues to support the use of MSGT as a noninvasive means of assessing embryo quality. [ABSTRACT FROM AUTHOR]

OBJECTIVE: Studies have suggested single embryo transfer (SET) could prevent risks from multiple gestations resulting from ART. However, embryos are currently selected by morphological appearance and developmental rate, which have been shown inadequate to ensure success after SET. Because multiple embryos are created during IVF, SET often leads to cryopreservation of super numeral embryos for later transfer attempts. However, cryopreservation has its own inherent risks to embryo viability. The objective of this study was to identify if embryo density can be used to detect cryodamage. DESIGN: Culture based study. MATERIALS AND METHODS: Previous research from this lab suggested embryo weight could detect cryodamage in sheep. To further examine this observation, mice embryos were cultured to blastocysts. Fresh blastocysts were analyzed using a modified specific gravity technique (MSGT). Blastocysts were then frozen using global® Blastocyst Fast Freeze® Kit. Embryos were stored in cryotanks for a minimum of two weeks. Embryos were thawed with global® Blastocyst Fast Freeze® Thawing Kit. Thawed blastocysts were then reevaluated using the MSGT. Blastocysts were cultured for 48 hours. Survival was determined by blastocysts hatching out of zona pellucida. RESULTS: Data from an earlier sheep study suggest a difference in the density of embryos in sheep that conceived verses those who did not (P < 0.046). Embryos with average to slow descent times (low density) blastocysts established more pregnancies that survived to term than faster descending blastocysts, which often did not establish pregnancy at all. Post-thaw mice embryo data supported sheep study with embryos with average to slow descent times hatching at a higher rate than embryos that descended rapidly thru the MSGT (P < 0.029). Mice embryos embryos that showed fewer differences, which had similar weights pre-freeze and post-thaw survived at a greater rate than embryos with large differences in weight (P < 0.016). CONCLUSION: Embryo density could suggest biochemical information that cannot be determined from morphological assessment. Cryodamage can be detected by variability of embryo density, possibly because damaged embryos have lost the ability to osmoregulate themselves due to membrane disruption, making them denser. Current studies are examining if MSGT can determine embryo sex due to weight differences in X and Y chromosomes. This data continues to support the use of MSGT as a noninvasive means of assessing embryo quality. [ABSTRACT FROM AUTHOR]