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.
Pathophysiology
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)
Usually the placenta attaches to the endometrium. This allows the placenta to separate cleanly during the third stage of labour, after delivery of the baby.
With placenta accreta, the placenta embeds past the endometrium, into the myometrium and beyond. This may happen due to a defect in the endometrium. Imperfections may occur due to previous uterine surgery, such as a caesarean section or curettage procedure. The deep implantation makes it very difficult for the placenta to separate during delivery, leading to extensive bleeding (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 (e.g. for miscarriage or abortion)
- Previous caesarean section
- Multigravida
- Increased maternal age
- Low-lying placenta or placenta praevia
Presentation
Placenta accreta does not typically cause any symptoms during pregnancy. It can present with bleeding (antepartum haemorrhage) in the third trimester.
It may be diagnosed on antenatal ultrasound scans, and particular attention is given to women with a previous placenta accreta or caesarean during scanning.
It may be diagnosed at birth, when it becomes difficult to deliver the placenta. It is a cause of significant postpartum haemorrhage.
Management
Ideally, placenta accreta is diagnosed antenatally by ultrasound. This allows planning for birth.
MRI scans may be used to assess the depth and width of the invasion.
A specialist MDT should manage women with placenta accreta. Patients may require additional management at birth due to the risk of bleeding and difficulty separating the placenta. This may include:
- Complex uterine surgery
- Blood transfusions
- Intensive care for the mother
- Neonatal intensive care
Delivery is planned between 35 to 36 + 6 weeks gestation to reduce the risk of spontaneous labour and delivery. Antenatal steroids are given to mature the fetal lungs before delivery.
The options during caesarean are:
- Hysterectomy with the placenta remaining in the uterus (recommended)
- Uterus preserving surgery, with resection of part of the myometrium along with the placenta
- Expectant management, leaving the placenta in place to be reabsorbed over time
Expectant management comes with significant risks, particularly bleeding and infection.
The RCOG guideline (2018) suggests that if placenta accreta is seen when opening the abdomen for an elective caesarean section, the abdomen can be closed and delivery delayed whilst specialist services are put in place. If placenta accreta is discovered after delivery of the baby, a hysterectomy is recommended.
Last updated September 2020