There is a difference between the dark zone and the gestational sac, which is the primitive placental tissue, a small embryo wrapped in amniotic membrane and vascular network, the initial form of pregnancy. The dark zone, on the other hand, can be the predecessor of the gestational sac, a stopped developing gestational sac, or an accumulation of blood in the uterine cavity. In a normal intrauterine pregnancy, the dark zone will first appear in the ultrasound, and the dark zone will grow to a certain size and develop into a gestational sac. At this time, it can be called early pregnancy period, later the dark area in the uterus will continue to grow and develop into a gestational sac, so the dark area in the uterus is the early manifestation of gestational sac. In some cases, the embryo is not of good quality and stops developing at this time, so it may not develop into a gestational sac. After observing for a period of time, review the ultrasound and compare the results before and after. It should be scraped for pathology to further clarify whether it is a gestational sac or not. Therefore, it is recommended to go to the hospital to review the ultrasound after 1-3 weeks after the appearance of the intrauterine dark area, if it shows dark area, or no fetal heart or fetal bud, it is usually not a gestational sac, but may be fetal abortion or accumulation of blood in the uterine cavity.