Maternity Nursing Q 208
In placenta previa marginalis, the placenta is found at the:
A. Internal cervical os partly covering the opening.
B. External cervical os slightly covering the opening.
C. Lower segment of the uterus with the edges near the internal cervical os.
D. Lower portion of the uterus completely covering the cervix.
Correct Answer: C. Lower segment of the uterus with the edges near the internal cervical os
Placenta marginalis is a type of placenta previa wherein the placenta is implanted at the lower segment of the uterus thus the edges of the placenta are touching the internal cervical opening/os. The normal site of placental implantation is the upper portion of the uterus.
Option A: Marginal placenta previa is where the placental edge is within 2cm of the internal os. Nearly 90% of placentas identified as “low lying” will ultimately resolve by the third trimester due to placental migration. The placenta itself does not move but grows toward the increased blood supply at the fundus, leaving the distal portion of the placenta at the lower uterine segment with relatively poor blood supply to regress and atrophy.
Option B: The trophoblast adheres to the decidua basalis of the endometrium, forming a normal pregnancy. Prior uterine scars provide an environment that is rich in oxygen and collagen. The trophoblast can adhere to the uterine scar leading to the placenta covering the cervical os or the placenta invading the walls of the myometrium.
Option D: Migration can also take place by the growing lower uterine segment thus increasing the distance from the lower margin of the placenta to the cervix.