PLACENTA PRAEVIA

PLACENTA PRAEVIA

DEFINITION:

It is defined as bleeding from or into the genital tract after the 28^th weeks of pregnancy but before the birth of the baby.

PLACENTA PRAEVIA

Definition:

When the placenta is implanted partially or completely over the lower uterine segment it is called “Placenta Praevia”.

ETIOLOGY

The exact cause of implantation of the placenta is the lower segment is not known. The following theories are postulated.

Ø Dropping Down theory: The fertilized ovum drop down and is implanted in the lower segment. Poor decidual reaction in the upper uterine segment may be the cause.

Ø Persistence of chorionic activity: In the decidua capsulairs and its subsequent development in to capsular placenta which come in contact with decidua vera of the lower segment can explain the formation of lesser degree of placenta praevia.

Ø Defective decidua

Ø Big surface area of the placenta is in twins may encroach on to the lower segment.

The predisposing factors for placenta praevia are —

a) Multiparity

b) Increased maternal age (> 35 years)

c) History of previous caesarean section or any other scar in the uterus (myomectomy or hysterotomy).

d) Placental size (mentioned before) and abnormality (succenturiate lobes).

PATHOLOGICAL ANATOMY:

Ø Placenta: The placenta may be large and thin.

Ø Umbilcal Cord: The cord may be attached to the margin (battledore) or into the membrane (velamentous).

Ø Lower Uterine Segment: Due to increased vascularity, the lower uterine segment & the cervix becomes soft and more friable.

Ø Type — I (Law-lying): The major part of the placenta is attached to the upper segment and only the lower margin encroaches onto the lower segment but not upto the os.

Ø Type — II (Marginal): The placenta reaches the margin of the internal os but does not cover it.

Ø Type — III (Incomplete or partial central): The placenta covers the internal os partially (covers the internal os when closed but does not entirely do so when fully dilated)

Ø Type — IV (Central or total): The placenta completely covers the internal os even after it is fully dilated.

For clinical purpose the types are graded into mild degree (Type-I and II anterior) and major degree (Type-II posterior, III and IV).

Dangerous placenta praevia:

It is the name give to the type II posterior placenta praevia.

Causes of Bleeding:

As the placental growth slows down in later month and the lower segment progressively dilates. This leads to opening up of utero-placental vessels and leads to any episode of bleeding. As it is a physiological phenomenon which leads to the separation of placenta the bleeding is said to be inevitable.

The Mechanism of Spontaneous control of bleeding are:

1) Thrombosis of the open sinuses.

2) Mechanical pressure by the presenting part.

3) Placental infraction.

Placental Migration:

Ultrasonography at 17 weeks of gestation reveals placenta covering the internal os in about 10% of cases. Repeat ultra sonography at 37 week showed no placenta in the lower uterine segment in more than 90% of cases.