A10. Placenta praevia

Page created on December 1, 2021. Last updated on January 20, 2022 at 11:11

Definition and epidemiology

Placenta praevia refers to the situation when the placenta partially or completely covers the internal os of the cervix. This makes vaginal birth impossible and increases the risk for preterm delivery and severe postpartum haemorrhage. Also related are the marginal and low-lying placentas.

Placenta praevia is associated with the placenta accreta spectrum disorders (accreta, increta, percreta).


The cause of placenta praevia is unknown. Some risk factors include:

  • Previously damaged endometrium
  • Previous uterine surgery (C-section, etc.)
  • Advanced maternal age


  • Complete placenta praevia – placenta completely covers the internal os
  • Partial placenta praevia – placenta partially covers the internal os
  • Marginal placenta praevia – placenta reaches the margin of the internal os (but does not cover it)
  • Low-lying placenta – placenta lies within 2 cm of the internal os

Clinical features

Placenta praevia may present as painless vaginal bleeding during the last half of the pregnancy, or routinely during routine ultrasound screening. 90% of women with placenta praevia (which doesn’t resolve by week 20) will have antepartum vaginal bleeding. This bleeding may be severe.

Diagnosis and evaluation

The diagnosis is made based on ultrasound, either transvaginal or transabdominal.

In cases where placenta praevia is suspected or confirmed, digital vaginal examination is forbidden, as it can cause massive haemorrhage.

In many cases low-lying placenta and placenta praevia will migrate away from the internal os as the pregnancy continues and therefore resolve itself, not requiring treatment. Placenta praevia diagnosed early in the pregnancy should be followed up by ultrasound at 28 – 32 weeks of gestation to see whether it has spontaneously resolved or not. If it has not resolved by that time, a repeat ultrasound control can be made in week 36.


Patients with placenta praevia which has not resolved by week 36 require elective C-section at around week 37. Patients presenting acutely with severe active bleeding or foetal distress require emergency C-section.

I had this topic on my exam, and my examiner talked about giving tocolytics to decrease bleeding and the importance of having stored blood which corresponds to the mother’s in the institute in case of severe bleeding.

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