Trophoblasts (from Greek threphein: to feed, and blastos: germinator) are cells forming the outer layer of a blastocyst, which provide nutrients to the embryo and develop into a large part of the placenta. They are formed during the first stage of pregnancy and are the first cells to differentiate from the fertilized egg. Function Trophoblasts are invasive, eroding, and metastasizing cells of the placenta. Trophoblasts mediate the implantation of the embryo into the endometrium, but they are n… (More on Trophoblast)