The appearance of the yolk sac represents an intrauterine pregnancy because the embryo starts to develop after the appearance of the yolk sac, which is the precursor of the fetal bud. However, this does not mean that the pregnancy is “stable”, and a repeat ultrasound is needed to confirm that the embryo is alive when the fetal heart appears. The wall of the yolk sac is formed by the extra-embryonic mesoderm and the extra-embryonic endoderm, and is an important “bridge” between the mother and the fetus, responsible for transporting oxygen and nutrients to the fetus. As the fetus grows and develops, the yolk inside the yolk sac will be consumed and the yolk sac will gradually become smaller, which is a necessary process in fetal growth and development. Therefore, the appearance of the yolk sac means that the pregnancy is successful, but subsequent testing of the fetal buds and heartbeats is needed to determine the extent of fetal growth and development. After the pregnancy is confirmed to be intrauterine, the pregnant woman should maintain emotional stability, relax, pay attention to rest, avoid fatigue and strenuous exercise, and eat a balanced and nutritious diet. The fetus will be relatively stable after the 12th week of pregnancy and the middle stage of pregnancy.