Placenta previa (Implantation of placenta in lower uterus)

When the placenta is implanted partially or completely over the lower uterine segment,
it is called placenta previa. When the inelastic placenta sheared off by the dilation of
lower uterine segment for expulsion of fetus, leads to bleeding.

Incidence - 1 in 200 deliveries in the hospital.

Cause -
The exact cause of implantation of the placenta in the lower segment is not known.
It is more common in women who have:
- Abnormally shaped uterus 
- Many previous pregnancies
- Multiple pregnancy (twins, triplets, etc.)
- Due to history of surgery, c-section, previous pregnancy, or abortion.

Women who smoke or have their children at an older age may also have an increased risk.

Types or degrees -
There are 4 types of placenta previa depending upon the degree of extension of placenta
to the lower segment.

1. Type I (low lying) - The major part of the placenta is attached to the upper segment
   and only the lower margin encroaches to the lower segment but not upto the cervical
   os (opening).

2. Type II (marginal) - The placenta reaches the marginal of the internal os but not cover it.

3. Type III (incomplete or partial central) - The placenta cover the internal os partially.

4. Type IV (central or total) - The placenta completely covers the internal os even after
    it is fully dilated.

Symptoms -
The only symptoms of placenta previa is vaginal bleeding. The classical features of bleeding
are sudden onset, painless, apparently causeless and recurrent.

Diagnosis -
This condition is diagnosed by ultrasonography.

Complication - 
Maternal -
- Antepartum haemorrhage with varying degree of shock
- Malpresentation
- Premature labour
- Early rupture of membranes
- Cord prolapse
- Retained placenta
- Subinvolution

Fetal -
- Low birth weight (LBW)
- Asphyxia
- Intrauterine death
- Birth injuries

Management -
Prevention : To minimize the risks, the following guidelines are useful.
- Adequate antenatal care to improve the health status of woman.
- Antenatal diagnosis of low lying placenta at 20 weeks with routine USG.
- Significance of ''warning haemorrhage'' should not be ignored.
- Family planning and limitation of births reduce the incidence of placenta previa.