Pre-embryo

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Pre-embryo

The organism that starts developing at fertilization when the zygote is formed by the joining of an egg and a sperm. It attaches to the lining of the uterus after about 7 days. It continues to develop until it forms an embryo, 9 to 11 days later. Up to 50 percent of all pre-embryos end up passing out of the uterus without ever becoming an embryo.