Placenta praevia (placenta previa AE) is a obstetric complication that can occur in the second or third trimester of pregnancy. It is a leading cause of antepartum haemorrhage (Censored pagel bleeding) and is characterised by the implantation of the placenta over or near the top of the cervix. It affects approximately 0.5% of all labours.

There are four types of placenta praevia:

• Type I - Placenta encroaches the lower segment of the uterus
• Type II - Placenta reaches, but does not cover, the top of the cervix
• Type III - Placenta covers the top of the cervix when it is closed but not when it is dilated
• Type IV - Placenta completely covers the top of the cervix

The cause of placenta praevia is unknown though the likelihood is thought to be increased by multiple pregnancy (twins or more), repeated pregnancy or a previous of Caesarean section.