Placenta praevia

The placenta is the organ that provides oxygen and nutrients to the baby during pregnancy. The placenta is usually attached to one of the inner walls of the uterus. 

Placenta praevia is the complete or partial insertion of the placenta into the lower segment of the uterus, which can block the internal cervical os, which is the exit route for the baby.

Depending on the position of the placenta to the orifice, it is classified into the following types

• Complete placenta praevia: the cervix is completely covered by the placenta.
• Partial placenta praevia: the cervix is partially covered by the placenta.
• Marginal placenta praevia: the placenta reaches the edge of the cervix but does not extend beyond it.
• Low-lying placenta: the edge of the placenta is less than 2 cm from the cervix.

The exact cause is not known, but there are several contributing factors:

• Multiple pregnancy: the placenta takes up more volume and is more likely to obstruct the cervix.
• Anterior uterine scar: the incidence increases with the number of previous caesarean sections.
• Multiparity: parity and age over 35 years old.
• Smoking: doubles the risk.

This location can make it easier for bleeding to occur during pregnancy. These bleeds are usually mild, but can sometimes be serious and life-threatening for the baby.
Placenta praevia can be life-threatening for both the baby and the mother. Placenta praevia is the most common cause of bleeding in the third trimester.

The definitive diagnosis is made by transvaginal ultrasound. Differential diagnosis must be made with vasa praevia, placental abruption and uterine rupture.
Treatment depends on the type of placenta praevia. In a complete placenta praevia: elective caesarean section from 38 weeks. If the placenta is marginal or low-lying and there is no bleeding, it is advisable to allow the birth to proceed spontaneously.