Spindle shape and volume differ in high- and low-quality metaphase II oocytes.

The proper development of embryos strongly depends on the quality of oocytes, so the evaluation of oocytes may be a useful initial step in in vitro fertilization procedures. Additionally, it enables embryologists to make more informed decisions regarding the treatments chosen for the patients and better manage patients' expectations. Optical coherence microscopy (OCM) allows for non-invasive 3D visualization of intracellular structures, such as spindles or nuclei, which have been linked to the success of embryonic development. Here, we applied a mouse model to examine whether OCM imaging could be used in the quality assessment of metaphase II (MII) oocytes. We showed that quantitative parameters describing the shape and volume of the MII spindle were associated with the quality of the resulting embryos, including the likelihood of blastocyst formation and the embryos' ability to differentiate the trophectoderm and primitive endoderm, but not the epiblast. We also created a multivariate linear regression model, combining OCM-based quantification of MII spindles with morphokinetic analysis of the embryos, that allowed for improved evaluation of the embryo quality. Finally, we proved that OCM does not interfere with the viability of the scanned cells, at least during the preimplantation development. Therefore, we believe that OCM-based quantitative assessment of MII spindles can improve the oocyte and embryo selection in IVF procedures.