Placenta accreta

• Placenta accreta refers to when the placenta implants deeper, through and past the endometrium, making it difficult to separate the placenta after delivery of the baby. It is referred to as placenta accreta spectrum, as there is a spectrum of severity in how deep and broad the abnormal implantation extends.
• There are three layers to the uterine wall:

  • Endometrium, the inner layer that contains connective tissue (stroma), epithelial cells and blood vessels
  • Myometrium, the middle layer that contains smooth muscle
  • Perimetrium, the outer layer, which is a serous membrane similar to the peritoneum (also known as serosa)
• Pathophysiology:

  • Usually the placenta attaches to the endometrium - allows to separate cleanly during 3rd stage of labour
  • With placenta accreta, the placenta embeds past the endometrium, into the myometrium and beyond
  • May happen due to a defect in the endometrium
  • Deep implantation makes it very difficult for the placenta to separate during delivery, leading to an extensive postpartum haemorrhage
• There are three further definitions, depending on the depth of the insertion:

  • Superficial placenta accreta is where the placenta implants in the surface of the myometrium, but not beyond
  • Placenta increta is where the placenta attaches deeply into the myometrium
  • Placenta percreta is where the placenta invades past the myometrium and perimetrium, potentially reaching other organs such as the bladder
• Risk factors:

  • Previous placenta accreta
  • Previous endometrial curettage procedures
  • Previous caesarean section
  • Multigravida
  • Increased maternal age
  • Low-lying placenta or placenta praevia
• Presentation:

  • Does not typically cause any symptoms during pregnancy - can present with bleeding in the third trimester
  • May be diagnosed on antenatal ultrasound scan
  • May be diagnosed at birth when it becomes difficult to deliver the placenta
  • Cause of significant post partum haemorrhage
• Investigations:

  • Ideally, placenta accreta is diagnosed antenatally by ultrasound - allows planning for birth
  • MRI scan may be used to assess the depth and width of the invasion
• Management:

  • Managed by specialist MDT
  • Delivery is planned between 35 to 36+6 weeks gestation to reduce risk of spontaneous labour and delivery. Antenatal steroids are given to mature the fetal lungs
  • Options during caesarean:
  • Hysterectomy with the placenta remaining in the uterus (recommended)
  • Uterus preserving surgery - resection of part of the myometrium along with the placenta
  • Expectant management - leaving the placenta in place to be reabsorbed over time (very high risk of bleeding and infection)