Non-invasive and highly sensitive measurement of the respiratory activity of individual human embryos by scanning electrochemical microscopy

Abstract

OBJECTIVE: Oxygen consumption is an ideal indicator of embryo quality. Recently we developed a novel cell respiration measuring system, scanning electrochemical microscopy (SECM). This technique is a useful method for evaluating embryo quality that correlates metabolic respiration with morphological quality, developmental potential, and pregnancy rate following embryo transfer in bovine. DESIGN: In this study, we employed SECM to accurately determine the oxygen consumption of single, identical human embryos at different developmental stages. MATERIALS AND METHODS: Surplus human embryos which remained unused upon completion of fertility treatment were used in this study. Their use in academic research was consented to by the patient. The embryos were cultured in Sydney IVF Cleavage Medium until Day 3, after which they were cultured in Sydney IVF Blastocyst Medium. Oxygen consumption by individual human embryos was quantified by a modified SECM measuring system. The microelectrode was scanned along the sample and the oxygen consumption rate was calculated with custom software based on spherical diffusion theory. Some embryo were examined using a transmission electron microscope. RESULTS: The oxygen consumption rates (×1014 mol s-1) of single embryos were low at 2-8-cell stages (0.51±0.05) but increased by the morula (0.61±0.11) and early blastocyst (0.72±0.06) stages. Later blastocysts exhibited even higher oxygen consumption rates (1.00±0.19). Ultrastructural studies revealed that most mitochondria in embryos up to the 8-cell stage were immature and had a spherical or ovoid shape. However, by the morula stage, mitochondria have elongated. This morphology is even more pronounced in mitochondria present in blastocysts with high oxygen consumption rates. CONCLUSIONS: SECM can be applied to measure the oxygen consumption of single human embryos at various developmental stages. The maturation of mitochondria correlated with the increase of oxygen consumption rate during the development of embryos. The development of mitochondria may be an important factor in embryo quality. The SECM technique may be a valuable tool for accurately assessing the quality of embryos as this approach provides objective criteria for evaluating embryos that complements morphological evaluation.