Oocyte zona pellucida and meiotic spindle birefringence as a biomarker of pregnancy rate outcome in IVF-ICSI treatment

Objectives: IVF-ICSI procedures are accompanied by a continuous search for predictors of ART outcome. The properties of zona pellucida (ZP) have been believed to reflect the history of oocyte cytoplasmic maturation. The meiotic spindle (MS) is crucial for chromosomal alignment and proper separation of the maternal chromosomes. There is data suggesting that birefringent ZP and MS can clinically predict the oocyte quality and developmental potential of an embryo. The aim of the study was to examine the possible effect of ZP birefringent properties and MS visualization and localization as valuable predictors of IVF-ICSI effectiveness. Material and methods: The prospective study was performed during a 16-month period. A total of 51 patients undergoing in vitro fertilization - embryo transfer (IVF-ET) treatment procedure with intracytoplasmic sperm injection (ICSI) were included. Controlled ovarian hyperstimulation (COH) was done using either a long n=32 (62.75%) or an antagonist protocol n=19. In the group of the 48 examined patients (aged 25-40), 46 ET were performed, resulting in 24 positive pregnancy tests and 19 (39.59%) clinical pregnancies. Oocytes were examined as follows: ZP birefringence autoscoring (OCTAX PolarAIDE), numeral autoscoring, thickness and clinical evaluation; MS visualization, if MS was visualized, localization of MS in relation to the polar body (PB). Results: On day 3, 64.3% of the embryos were of good and 40.3% were of top quality. Visible differences, not statistically significant, were observed in the numeral score of ZP between oocytes selected and non-selected for ET. In cases when embryos were not of good or top quality, ZP score was higher (p=0.005 p=0.001). ZP manual evaluation indicated significantly stronger birefringence when pregnancy was not achieved (p=0.022). The rate of MS positive oocytes was the highest in the group with pregnancy, but it did not reach statistical significance (p=0.471). The MS localization in relation to the PB was in most oocytes very close (<45o) in 70.9% and not different in the studied groups. Conclusions: Unexpected polarization microscopy imaging and rating of ZP and MS cannot be a direct predictor of the IVF outcome.