Pronuclear Scoring in Human In Vitro Fertilization

Abstract

Historically, the introduction of pronuclear scoring was observational and from two different perspectives, even if the morphological features score resulted in the same outcome and conclusions. Pronuclear scoring involves descriptions of the nucleolar precursor bodies (NPBs) which are clearly visible spherical structures observed in the nuclei of the fertilized oocyte, or for that matter, in the nuclei of any actively dividing cells. The two scoring systems looked at the same parameters of the NPBs, namely, their alignment, number, and relative size in the newly formed male and female nucleus. These parameters were shown to be predictive of continued development and resultant outcome. In the 1999 model from Tesarik et al., the NPBs and their pattern were used as an indicator of sperm decondensation and function during ICSI cases. The model of Scott et al. described patterns of NPBs in the fertilized oocyte and how these changed, how they were related to a halo seen in the oocyte and the dynamic nature of fertilization, and how the patterns correlated with continued embryo viability. Pronuclear scoring is descriptive and based on NPB and nuclear morphology and accomplished at the time of fertilization check, which should be between 16 and 18 h postinsemination. Although descriptive, the patterns have a biological basis and are predictive of development based on cell cycle and structure and function of the nucleus and nucleolus.