Question 27

A 24 yo G3P1 undergoes ultrasound at 20 weeks showing an anterior placenta previa. Her history is notable for a prior uncomplicated SVD and a first trimester loss. Repeat ultrasound at 32 weeks shows that the edge of the placenta is 2.1 cm from the internal cervical os. What is the best next step in management?

Answer Choices:

Routine antenatal care

Repeat ultrasound at 37 weeks

Cesarean delivery at 36 weeks

Cesarean delivery at 39 weeks

Correct Answer:

Routine antenatal care


  • Placenta previa involves the leading edge of the placenta covering or abutting the internal cervical os

  • Historical terminology referred to previas as complete, incomplete or marginal, but these were often difficult to distinguish on ultrasound so the currently accepted diagnosis is placenta previa which incorporates all of these old terms

  • Low-lying placenta is when the edge of the placenta does not touch the internal os, but is located within 2 cm of the os.

  • Due to trophotropism, the cephalad portion of the placenta grows more than the caudal portion due to disproportionate blood supply to the uterine fundus (so many previas resolve in the third trimester)

  • If diagnosed with previa in the 2ndtrimester, a repeat ultrasound is recommended at 32 weeks.

  • If the leading edge is more than 2 cm from the internal os, this is normal and there is no indication for additional management

  • If the placental edge is less than 2 cm from the os or continues to cover the os, a repeat ultrasound sound be performed at 36 weeks

  • Delivery for placenta previa typically occurs between 36-37 weeks