Placenta praevia

Disease class: Obstetric labor complications

Disease class: Placenta diseases

Placenta praevia describes a placenta lying wholly or partly in the lower uterine segment

Epidemiology

• 5% will have low-lying placenta when scanned at 16-20 weeks gestation
• incidence at delivery is only 0.5%, therefore most placentas rise away from cervix

Associated factors

• Multiparity
• Multiple pregnancy
• Embryos are more likely to implant on a lower segment scar from previous caesarean section

Clinical features

• Shock, consistent with visible loss
• No pain
• Uterus not tender
• Lie and presentation may be abnormal
• Foetal heart usually normal
• Coagulation problems rare
• Small bleeds before large

Investigations

• Placenta praevia is often picked up on the routine 20 week abdominal ultrasound.
• The RCOG recommend the use of transvaginal ultrasound as it improves the accuracy of placental localisation and is considered safe.

Classical grading

• I - placenta reaches lower segment but not the internal os
• II - placenta reaches internal os but doesn't cover it
• III - placenta covers the internal os before dilation but not when dilated
• IV - placenta completely covers the internal os