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

Abstract

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.

An oocyte score for use in assisted reproduction

“…The oocyte plasma membrane response to penetration with an ICSI pipette has also been suggested to be a useful determinant of oocyte quality [46]. Many other parameters have also been analysed in oocytes such as zona pellucida thickness, spindle birefringence and extracellular dysmorphisms [36,47,48]. Results vary as to whether distinct oocyte dysmorphisms have any relation to fertilisation and development rates, probably due to a discordance in the scoring of these dysmorphisms [50], although an effect on pregnancies is often noted [21,36,47,50].…”

Effects of maternal ageing on ICSI outcomes and embryo development in relation to oocytes morphological characteristics of birefringent structures

“…Battaglia et al (1996) have shown that age-related disturbances of meiotic spindles predispose oocytes to disorganization of chromosomal segregation and successful aneuploidy, maturation arrest and the corresponding lower fertilization rates. Shen et al (2006) compared the mean retardance and length of the meiotic spindle and maternal age in groups who were either ࣘ30 years, 31-35 years or ࣙ36 years in age. There was an age-related reduction in mean retardance value of the transfer oocytes from older patients.…”

Polarized light microscopy-detectable structures of human oocytes and embryos are related to the likelihood of conception in IVF

“…Some studies suggested that PLM analysis of the MS in fresh and frozen oocytes could be useful in identifying eggs with a high potential of originate embryos leading to pregnancy [5][6][7][8]. On the other side, however, the value of MS assessment by PLM was questioned by a study performed by confocal microscopy, that showed that PLM gives only an approximate idea of the real shape and structure of the spindle, as its results do not match with those obtained using fixation, staining and confocal microscopy [14].…”

“…A similar procedure was followed to acquire data of embryos. The manual measurement of MS major axis length was performed drawing a line scan as previously described [6,8] (Fig. 1).…”

“…Several studies on human oocytes reported that some birefringent characteristics of the meiotic spindle (MS) [5][6][7][8] and of the zona pellucida (ZP) [8][9][10][11][12][13] were associated with a high level of structural organization of the oocyte and could be positively related to the developmental potential of the embryo derived from it. These reports, however, were not fully convincing; especially those dealing with the MS were thoroughly criticized because the comparative analysis of the MS by confocal microscopy showed important discrepancies with PLM data [14].…”