A Prospective Study of Oocyte Zona Pellucida Mechanics as a Predictor of Embryo Implantation: A Novel Tool for Embryo Selection

Introduction
The ZP undergoes extensive mechanical deformation at the time of blastocyst expansion and hatching. No study examined the effect of the ZP mechanics properties on hatching and implantation.

Aim
To examine if ZP deformation during the ICSI procedure can predict embryo implantation.

Methods and Material
One hundred and sixty-four oocytes were aspirated from 28 IVF patients. The oocytes were tested for ZP shear modulus (SM-the ability to resist shape change). Thirty-nine embryos were transferred and the implantation rate (IR) was measured. Images of ICSI procedures were used to construct computational models that were compared to deformation observed in ICSI procedure during oocyte suction. SM was compared between implanted and non-implanted embryos using chi-square test.

Results
A great variance was observed in the SM of oocytes aspirated from the same patient (0.0001-0.00065 Mega Pascale-MPa). A significant correlation was found between the value of the ZP SM and IR when comparing oocytes inside and outside of a specific SM-range (0.0002-0.0004 MPa). Ten out of the 16 (62.5%) implanted embryos, displayed shear modulus values in the specific range, with only 2 implanted embryos out of 23 that were outside the range (8.7%) P=0.037, OR-1.85. No correlation was found between ZP shear modulus and ZP thickness, oocyte diameter, embryo quality or patient’s age.

Conclusions
The ZP shear modulus which is determined early at the time of sperm injection can be used as a novel method for embryo selection, consequently leading to a higher embryo implantation rate. Our methodology can be implemented with no major changes in the current ICSI procedure.