Specific gravity device can predict embryo and oocyte quality, survival of embryo cryopreservation and aid in the establishment of pregnancy



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The first documented use of embryo transfer (ET) was performed in rabbits by Walter Heape in 1891. This led to the advancement of assisted reproductive technologies (ARTs) which would eventually lead to successes in ET in other species, in vitro fertilization (IVF) and use of cryogenics in ART. ET and IVF eventually graduated from being experimental procedures to routine methods to treat infertility and maximize superior genetics in animal breeding programs. In order for ET and IVF to become routine procedures, non-invasive methods to predict oocyte and embryo developmental potential had to be discovered to make these procedures successful. Currently, the most reliable and commonly used method to predict oocyte and embryo quality is by a visual morphological assessment through a light microscope. This method requires trained personnel to visually inspect the embryo or oocyte to identify abnormalities and developmental stage. Grading systems have been developed to classify embryo and oocyte qualitative properties but are dependent on the judgement of the one performing the morphological assessment. The morphological assessment is noninvasive and inexpensive, but is highly subjective and provides little information about biochemical properties and survival of cryopreservation.
Fluctuations in temperature, pH and osmotic shock often contribute to the lessened viability of oocytes and embryos. Differences in biochemical constituents from the same maternal cohort can affect oocyte and embryo competency. However, these factors do not always result in inferior quality grades as determined in a morphological analysis. A quantitative method to predict oocyte and embryo quality and differentiate between viable and non-viable oocytes and embryos would greatly increase success rates of ET and IVF. This laboratory designed a new device and method, the specific gravity device (SGD), to enhance oocyte and embryo selection to increase success of IVF and ET and promote single embryo transfer. The SGD allows for a quantitative estimation of oocyte and embryo biochemical properties and viability by measuring oocyte or embryo buoyancy. Studies were performed in mice and sheep to determine of the SGD can predict quality, viability, and establish healthy pregnancies which survive to term. The results of these experiments demonstrate SGD can be used as a non-invasive quality assessment to supplement the current morphological analysis. SGD does not harm the development of early stage embryos and may even contribute a microfluidic effect to enhance development. SGD can help differentiate between viable and non-viable oocytes and embryos and is the first documented non-invasive method to determine blastocyst survival of cryopreservation. Preliminary breeding trials in sheep demonstrated cryopreserved blastocysts can survive exposure to SGD and produce healthy lambs. SGD appears to be a superior technology to assist in the selection of oocytes and embryos to be used in further ART.



Embryo, Oocyte, Selection Technique, Buoyancy, Specific Gravity Device