The diagnosis of placenta previa has shifted from clinical examination of the dilated cervix to sonographic assessment of the closed internal os, resulting in terminology confusion. If the cervix is closed, the distinction between a placental edge at the cervical margin and one partially covering the os is neither reliable nor clinically important. Cesarean delivery is recommended if the placenta reaches the cervical margin at time of delivery, and this entity may be grouped with placenta previa. Partial previa should probably be restricted to those with cervical dilatation. The terms marginal previa and low-lying placenta have been used interchangeably. However, if the placenta implants in the lower uterine segment but does not reach the cervix, low-lying placenta is preferred, and vaginal delivery may be achieved, depending on placental-os distance and presence of bleeding. Limited data suggest that if the placenta is within 2 cm of the os-low-lying placenta, cesarean delivery is performed for bleeding in one-third of cases.
Keywords: Low-lying placenta; Marginal previa; Placenta previa; Placenta-os distance.
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