The different stages of human development. The fetal stage of human development begins around 8 weeks after fertilization — when the embryo has developed its basic form — and lasts until birth. It’s a transformation unlike any other: from a 1-inch-long, bean-shaped body to a fully formed newborn, 20 inches (50 cm) long and weighing around 7.5 pounds (3.4 kg). By the end of the first trimester, most major organs are in place. The heart has been beating since about week 6, but now it’s pumping blo

This is the exact moment life takes hold. In a world-first experiment, scientists have filmed the exact moment a human embryo implants into tissue, revealing a surprisingly aggressive and forceful process. The footage offers new insight into one of the most mysterious and fragile stages of life — one that determines whether a pregnancy will begin at all. Embryo implantation happens five to six days after fertilization, when the embryo is just 100–200 cells. At this stage, it’s far too small to d