The lower edge of the placenta reaches the edge of the endocervical os is the position of the lowermost edge of the placenta in relation to the endocervical os, and needs to be analyzed in relation to the week of gestation. If the lower edge of the placenta reaches the edge of the endocervical os before 28 weeks of gestation, the placenta previa can be described as a placenta previa. If the ultrasound indicates that the lower edge of the placenta reaches the endocervical os, after 28 weeks of gestation, the diagnosis of marginal placenta previa can be made. Marginal placenta previa belongs to one kind of placenta previa. It usually has no obvious clinical manifestations and does not require special treatment. If the lower edge of the placenta reaches the edge of the endocervical os, regular monitoring is needed to assess the position of the placenta, do not have sex for the time being, avoid strenuous exercise, and consult a doctor if vaginal bleeding occurs, and choose the mode of delivery at the end of the pregnancy in conjunction with the position of the placenta.