18 weeks pregnant uterus posterior wall, position slightly low suggests that the placenta is located in the posterior wall of the uterus accompanied by the placenta in a low state, should pay attention to good labor and delivery examination. The placenta is located in the posterior wall of the uterus at 18 weeks’ gestation and its position is slightly low is a term commonly used in ultrasound examination, suggesting that the lower edge of the placenta is less than 3 centimeters away from the uterine orifice, and the placenta is in a low lying state, after the diagnosis of low lying state of the placenta, patients should pay attention to rest, regular checkups, and avoid strenuous activities, so as not to lead to hemorrhage, abortion, and other undesirable consequences. Some patients with low lying placenta can return to normal position as the uterus enlarges and the lower part of the uterus is elongated with the increasing of pregnancy months; some patients with placenta position not returned to normal after 28 weeks of pregnancy can be diagnosed with placenta praevia, which has the risk of placenta previa, infection and hemorrhage, and can seriously jeopardize the life of both mother and child. Regular obstetric examination and standardized treatment under the guidance of professional physicians can ensure the safety of mother and child and avoid adverse pregnancy outcomes.