There is a relationship between fetal buds and fetal heart and HCG levels. HCG is a substance secreted by gestational trophoblast cells, which is a system of active embryonic development in the body. When the egg meets the sperm and fertilization is successful it begins to differentiate the embryo, forming gestational trophoblast cells that begin to secrete HCG. HCG levels in early pregnancy began to double the growth trend, only when the HCG doubled to a certain level can promote the embryo buds fetal heart emergence, in ultrasound examination can be found in the fetal gestational sac of the development of fetal buds and whether there is a fetal heart. Generally speaking, if the HCG doubles normally, the fetal heart can be seen around 6 to 8 weeks of pregnancy through vaginal or abdominal ultrasound examination.