Placenta Praevia

Placenta praevia is described as an abnormally located placenta in the lower uterine segment, either completely or partially covering the uterine os. Incidence of 4-5 in 1,000 pregnancies. Bleeding is painless and presents as a fresh loss.

Placenta praevia is divided into four types:

• Type 1: The placenta encroaches into the lower uterine segment and lies within 5cm of the internal cervical os. Blood loss is minimal and vaginal delivery is achievable.
• Type 2: The placenta reaches the cervical os but does not cover it. Blood loss is moderate and fetal hypoxia is more likely to be present than maternal shock. Vaginal delivery is possible if the placenta is on the anterior uterine wall.
• Type 3: The placenta covers the cervical os but the placental site site is assymetrical, with most of the placenta being on one side of the cervical os. Bleeding is likely to be severe, particularly in late pregnancy, when the cervix begins to efface and dilate. Vaginal delivery is not possible, as the placenta precedes the fetus.
• Type 4: The placenta is centrally located over the cervical os. The risk of torrential haemorrhage is increased and makes caesarean section essential to save both mother and fetus.

http://www.patient.co.uk/showdoc/40000210/
Medforth, J., Battersby, S., Evans, M., Marsh, B. and Walker, A. (2006) Oxford Handbook of Midwifery. Oxford: Oxford University Press.