Placenta previa occurs when the placenta is implanted where?

Placenta previa is a condition characterized by the implantation of the placenta over or near the cervical os, which is the opening of the cervix that leads to the vagina. This condition can lead to complications during pregnancy, particularly in labor, because as the cervix dilates, the placenta can become detached or cause bleeding.

When the placenta is positioned over the cervical os, it can obstruct the birth canal, necessitating careful monitoring and often a cesarean delivery if the condition persists as the pregnancy progresses. Understanding the placement of the placenta is crucial for managing labor and delivery safely, hence the significance of its location in relation to the cervical os.

The other options describe positions such as the fundus, uterine wall, or an ectopic position in the Fallopian tube, which do not correspond to placenta previa and do not pose the same risks in terms of obstruction during delivery.