Is there fetal heart rate or fetal bud at 5 weeks pregnant? Early fetal development Development of the fetus at 5 weeks of pregnancy 5 weeks of pregnancy is the early stage of the fetus. At this time, the fetus is mainly a germ composed of three layers. The first layer is the ectoderm, which will form the placenta and amnion. The second layer is the mesoderm, which will become many of the organs and tissues of the fetus. The third layer is the endoderm, which will form the digestive system of the embryo.