To enable improved success rates of IVF, we developed the technology to optimize embryo selection with the highest implantation potential while ensuring no damage to embryos using zona elasticity as the selection criterion. In this communication we outline the biomechanics and safety of zona pellucida (ZP) elasticity measurement using the micro tactile sensor (MTS) system and demonstrate the specific changes in ZP elasticity during oocyte maturation, fertilization, and early embryo development. Zona hardening was demonstrated mechanically following fertilization at the pronuclear (PN) stage, and Young's modulus decreased gradually as the embryo developed. Evaluation of the quality of expanded blastocysts (EPB) showed that the quality of EPBs could also be evaluated from elasticity parameters. Furthermore, the observations indicated that ZPs of embryos generated in vivo were significantly harder than those of embryos generated in vitro at each stage. Preliminary results also indicated that denuded oocytes matured in vitro did not show zona hardening following parthenogenetic activation by strontium chloride, suggesting that sufficient maturation and consequent oocyte activation may be evaluated by increases in ZP elasticity. We conclude that MTS-elective single embryo transfer can be applied to human assisted reproductive technology to enable embryo quality evaluation in both early embryos and EPBs.