A placental blood pool is an abnormal structure occurring in the placenta, which is a pool of veins formed due to localized venous dilatation of the placenta in which blood is stagnant. During ultrasonography, round or oval dark areas of fluid of varying sizes can be seen in the substantial structures of the placenta. Placental blood pools are small in size and usually have no significant adverse effects in single cases and require no special treatment. If the placental blood pools are larger or more numerous, they can affect the blood flow exchange between the placenta and the fetus, potentially leading to fetal ischemia and hypoxia and affecting the healthy development of the fetus. A large placental blood pool can also easily lead to the occurrence of placental abruption. When there is a large or more placental blood pool, pregnant women should absolutely prohibit sexual intercourse and avoid physical labor and sports.