Placental blood sinus is usually dangerous only when it is more than 5cm and there are still symptoms, so it is necessary to strengthen the management of pregnancy. Placental blood sinuses, also called placental blood pools, are mostly formed when placental blood vessels fuse with each other, or when the placenta peels away from the uterine wall due to external forces. If there are no symptoms and only an ultrasound is indicated, it is important to strictly follow the doctor’s instructions to have regular labor and delivery checkups. However, when the diameter of the placenta is >5cm and there is abdominal pain and vaginal bleeding, it is dangerous and needs to be fully evaluated by a doctor before terminating the pregnancy. The placenta is an important organ to maintain fetal growth and development, and is an important intermediary for material exchange between the fetus and the mother. When ultrasound clinical examination suggests abnormalities of the placenta, such as placenta praevia and placenta previa, it is necessary to dynamically observe the changes of the placenta, strengthen the management of the pregnancy and terminate the pregnancy according to the specific conditions of the pregnant woman, in order to ensure the safety of mothers and infants.