Claudio Manna (Italy)
Objective assessment of oocyte quality is actually an important matter of investigation in assisted reproduction technology (ART) because of bioethical reasons, improvement of oocyte freezing-thawing techniques and limited predectivity of embryo score systems (1).
Morphological oocyte evaluations are still the standard for routine work in intracytoplasmic sperm injection (ICSI) (2), though they are highly subjective. It was demonstrated that morphological evaluation before ICSI helps to identify metaphase II (MII) oocytes with higher developmental potential (3).
New methodologies, including polar body diagnosis (PBD) (4), metabolomics (5), polarization light microscopy (6; 7; 8; 9; 10) and pattern recognition of processed images by special algorithms (11), have been proposed as methods to improve the objective selection of good quality oocytes.
In particular, the PolScope was used in a semiquantitative mode to evaluate the birefringence of the zona pellucida (ZP) (12) and the meiotic spindle (SP) of the metaphase II oocytes (7).
High zona pellucida birefringence (HZB) has been associated with a significant higher rate of embryo implantation and development to term in comparison to low zona pellucida birefringence (LZB) (9; 10). Oocytes with high fertilization rate show in general a birefringent SP (7; 10). Therefore there is a broad agreement that the analysis of ZP and SP birefringence represents a reliable objective criterion for good quality oocyte selection.
Also our laboratory observed the same results with polarized light microscopy and for this reason we consider the birefringence an objective way to evaluate the oocyte quality.