Placenta Previa : Why it occurs.

Here's a short discussion post on Placenta Previa Etiology.

So Placenta Previa is a dangerous condition that presents with bleeding after 28 weeks up to the 1st stage of labour. (So it could so happen that the baby needs to tear it open and come out - as it may cover the Os. Hence Previa , where Previa means 'In front of'. Of course the reality being that the placenta gets compressed and results in fetal Hypoxia along with bleeding ).

The main pathology is that the Placental gets abberantly deposited / implanted in the lower uterine segment in stead of the upper.

This could be due to :
1. Decidual area being defective in the upper segment (Due to maternal age , Multiparity, Curretage or Cesearan section in the past).
2. Large placenta - due to which some part may encroach over the lower segment. (Multiple pregnancy, Smoking etc).

Here's a way to remember the risk / etiological factors for this condition.

Risk Factors for Placenta Previa -

Mnemonic : M4 C3

M - Maternal Age - Decidua becomes weaker with age so the placenta ends up encroaching over the lower segment.
M - Multiparity (Similar reason. Especially in a grand multi para)
M - Multifetal pregnancy (Twins etc. There's less space in the fundal area hence gets lodged in the lower segment)
M - Maternal Serum AFP (Indicates high/persistent Chorionic activity - essentially invades into more and more of the Endometrium.)

C - Curretage - in the past if done , damages the uterine layer making the upper segment defective.
C - Caeserean sections in the past / other operations on the Endometrium/myometrium - Makes the uterus defective.
C - Cigarette smoking - causes Hypoxia to the baby leading to Placental Hypertrophy - larger placenta occupies larger area and may encroach downwards.

Hope this helped !
Stay Awesome and
Happy Studying !
~ A.P.Burkholderia