Placenta previa is an obstetric complication in which the placenta is inserted partially or wholly in the lower uterine segment. It is a leading cause of antepartum haemorrhage. It affects approximately 0.4-0.5% of all labours. In the last trimester of pregnancy the isthmus of the uterus unfolds and forms the lower segment. In a normal pregnancy the placenta does not overlie. If the placenta does overlie the lower segment, as is the case with placenta previa, it may shear off and a small section may bleed. The exact cause of implantation of the placenta in the lower segment is not known. The abdominal examination and ultrasonography helps to reveal the placenta previa. Immediate delivery of the foetus may be indicated if the foetus is mature or if the foetus or mother is in distress. Blood volume replacement, to maintain blood pressure and blood plasma replacement, to maintain fibrinogen levels, may be necessary.