Noninvasive Embryo Assessment Technique to Predict Embryo Cryodamage and Potential Sex Selection.

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]