Germinal Stage
This stage runs from conception till the second week of pregnancy. Blastocyst happens where cells grow rapidly to for a cyst. The cyst has three layers: ectoderm, mesoderm, and endoderm. The ectoderm layer is the nervous system and the skin. The mesoderm is the skeletal system and the muscles. Endoderm is the layer that develops into the respiratory and digestive systems.
Embryonic Stage
This stage lasts from three weeks to the ninth week. It is the most crucial part of the prenatal development. The blastocyst is now an embryo. Differentiation happens in this stage. It is the rapid growth of over 230 different cell types. The heart begins to pulse in this stage and the limbs start to form as numbs. This is the stage when defects form in the embryo.
Fetal stage
This is the stage most associated with pregnancy. It lasts from nine weeks till birth. The embryo is now called a fetus. It is categorized by 3 trimesters.