Fetal Development at 3 Weeks: Appearance and Formation

At 3 weeks, the fetus is still in its early stages of development and is only about 2-3 millimeters in length. It looks like a small, white C-shaped structure that is made up of three layers of cells: the ectoderm, mesoderm, and endoderm. The ectoderm will eventually become the skin, hair, and nails; the mesoderm will become the muscles, bones, and connective tissues; and the endoderm will become the digestive and respiratory systems.

At this stage, the fetus is still forming its major organs and body systems. The heart is beginning to beat, and the neural tube is starting to develop. The arms and legs are also starting to form, but they are still very small. The eyes and ears are also beginning to develop, but they are still very primitive.

By 3 weeks, the fetus is also starting to produce human chorionic gonadotropin (hCG), a hormone that is responsible for maintaining the pregnancy. hCG levels will continue to rise throughout the first trimester of pregnancy.