BEIJING, June 15 (Xinhua) -- Chinese researchers have captured the first high-resolution footage of human embryos during their first five days of development, leading to a major discovery as to why so many embryos fail to grow in the clinic.The study, led by researchers from Tsinghua University, located in Beijing, was published in the journal Cell.For couples undergoing in vitro fertilization (IVF) treatment, the journey in pursuit of a baby is not always successful. More than half of human fertilized eggs stop developing before reaching the blastocyst stage, which is when they are ready to be implanted into the mother's womb. This high rate of failure has puzzled scientists for a long time.To solve this mystery, the research team built a new type of microscope, namely a dual-view light sheet microscope. This advanced tool can capture clear images of living embryos over longer duration and without harming them.By studying more than 2,000 cell divisions in over 150 human and monkey embryos, the team discovered that more than 70 percent of embryos that stopped growing early had problems during their second cell division. Specifically, a structure called the spindle, which looks like a tiny thread machine and helps divide genetic material equally, was abnormal in such cases. This caused errors in chromosome segregation, leading to cell cycle arrest within the next few cell divisions.Additionally, the researchers found that centrosomes, organelles of the cell that help build the spindle, play a key role in these errors. When the number of centrosomes was wrong, the spindle could not function properly.Building on this finding, the team attempted to ameliorate these errors during the second cell division. They applied a low dose of a drug that targets centrosome replication. The result was impressive: the percentage of embryos with normal centrosomes increased from 40 percent to 80 percent. Notably, the drug had no effect on embryos that had normal centrosomes.In the fu...