Light retardance by human oocyte spindle is positively related to pronuclear score after ICSI

Disturbed spindle assembly increases risks of chromosome mal-segregation. Non-invasive polarization microscopy (PolScope) was employed in two centres to assess spindle integrity for the first time quantitatively in human oocytes from consenting patients undergoing intracytoplasmic sperm injection (ICSI) with respect to pronuclear (PN) score after fertilization. In one centre oocytes were selected before ICSI, in another selection was after ICSI according to PN score. In both centres, mean retardance of light by birefringent spindles in oocytes forming a pre-embryo with good PN score after ICSI was significantly higher compared with spindles in oocytes developing into a lower PN score pre-embryo with limited developmental potential (P < 0.001). Transfers involving oocytes with high retardance and at least one good PN score embryo resulted more frequently in a conception than transfers from oocytes with spindles of lower mean retardance and lower PN score embryos. There was a trend for an inverse relationship between age and magnitude of retardance in a small oocyte cohort. The study suggests that quantitative evaluation of mean retardance of light by the oocyte spindle predicts oocyte health, is related to PN score of the embryo and may be especially useful to assess oocyte quality in countries with legal restrictions to select after fertilization.