EVAN OTO / SCIENCE PHOTO LIBRARY EVAN OTO / SCIENCE PHOTO LIBRARY
An illustration of early embryonic and foetal development during pregnancy. The top row depicts blastocyst implantation in the uterus roughly seven days after conception (left), development of the embryonic disc and formation of the chorion and proliferating syncytiotrophoblast after 12 days (centre), and development of the chorionic villi, umbilical cord, and germ layers after 16 days (right). The middle row depicts an embryo at four weeks old with the developing placenta and umbilical vessels (left), and a developing foetus at ten weeks old (right). The figure at the bottom of the image shows a fully developed foetus and placenta in utero.
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