The human Zona-Pellucida shear modulus before and after fertilization and its implications in IVF embryo selection

Previous studies have shown a clear correlation between the value of the human ZP shear modulus and implantation potential. Nevertheless, the mechanical response of the ZP changes following fertilization due to a phenomenon termed Zona hardening were not demonstrated. The current study investigated the Zona hardening phenomenon using a computational approach based on oocyte specific clinical data taken from IVF procedures. By analysis of ZP deformation before and after fertilization the value of the ZP shear modulus was estimated. The results clearly show an increase in ZP shear modulus by an average factor of 1.768 ± 0.83 which is consistent with past studies. There is, however, great variability in the amount of Zona hardening for the different oocytes analyzed. It is shown, that while the value of the ZP shear modulus before fertilization is well correlated with embryo implantation potential, strengthening past observations, the ZP shear modulus estimated at days 2-3 after oocyte retrieval is not correlated with implantation.