creation date: 2026-01-10 21:20
tags: Pathologies
Placenta Accreta Spectrum
Background
Definitions
Placenta accreta spectrum (PAS) refers to a pregnancy condition in which the placenta attaches too deeply into the uterine wall and fails to detach after childbirth.
Placenta accreta: anchoring placental villi attach to the myometrium
Placenta increta: anchoring placental villi penetrate into the myometrium
Placenta percreta: anchoring placental villi pentrate through the myometrium to the serosa or adjacent organs
Pathogenesis
Normal placentation involves extravillous trophoblast invasion into the decidua which initiates spiral artery remodeling, immune modulation, and other parts of the process.
In cases of uterine scarring, the decidua is replaced with scar tissue which allows for tophoblasts to migrate closer/within the myometrium and thus “invading” the myometrium or serosa.
Risk factors
- Prior c-section (increases with number of c-sections)
- Placenta previa (most significant when in combination with prior c-sections)
- History of uterine surgery with endometrial disruption
- Maternal age >35
- Multiparity
- History of pelvic irradiation
- Manual removal of placenta
- Postpartum endometritis
- Infertility/infertility procedures
Clinical Presentation
Signs & Symptoms
Most cases are asymptomatic and discovered during obstetric ultrasound.
The first clinical finding is typically profuse hemorrhage at time of attempted manual placental separation.
History & Physical Exam
Prenatal history should capture risk factors and PAS often found incidentally on ultrasound.
Diagnosis
Criteria
Prenatal diagnosis
Can be made in patients with placental previa/low anterior placenta and risk factors. Characteristic ultrasound findings include:
- Lower uterine segment placental position
- Multiple placental lacunae
- Disruption of bladder line (normally continuous white line where bladder wall and uterine serosa interfaces)
- Loss of clear zone (normally hypoechoic area behind the placenta)
- Myometrial thinning
- Abnormal vascularity
- Abnormal uterine contour
- Exophytic mass
Work-up
Additional imaging
Role of MRI has not been clearly determined. It may allow for better visualization and preoperative planning.
Differential
Red Flags / Complications
The consequence of PAS is major hemorrhage when the placenta is removed due to the lack of a normal plane of clevage. Outcomes can include:
- Hysterectomy (common indication to control hemorrhage)
- Maternal morbidity
- Neonatal morbidity (preterm and SGA infants)
- Mortality
Management
Prenatal Care & Delivery Preparation
Prenatal care
Patients with suspected PAS should be counselled and advised to give birth at a centre capable of treatment.
Management follows those of placenta previa, which includes:
- Correction of iron deficiency anemia
- Administration of course of betamethasone between 23-34 weeks for pregnancies at risk of delivery within 7 days
- Administration of anti-D immune globulin if vaginal bleeding occurs in D-negative patient (unless fetus also D-negative)
- Avoid pelvic examination or rigorous physical activity
Preparation for delivery
The goal during and after delivery is to reduce risk of massive postpartum hemorrhage. This involves a multidisciplinary care team depending on involved organs.
- Scheduled delivery (to ensure optimal availability of personnel/facilities)
- At least 2 large-bore IV access
- Monitoring including cardiac output if needed
- Thromboembolism prophylaxis (often with pneumatic compression devices)
- Blood products
Delivery
Timing
Many patients will develop complications such as PPROM, preterm labour, or antepartum bleeding leading to an earlier delivery than planned.
There is no optimal gestational age for scheduled delivery but guidelines generally advise:
- 34+0 to 35+6 for stable patients
- Before 34+0 if patient at high risk of emergency delivery
Delivery beyond 36 weeks is not advised.
Cesarean hysterectomy
The standard of care is a c-section delivery followed by hysterectomy with the placenta left in situ.
Conservative management
In very select patients who want to preserve fertility, uterine conservation may be possible.
- Expectant management with placenta left in situ
- Placental resection
Unexpected placenta accreta
In cases where PAS is discovered following delivery (eg. signs seen following c-section or hemorrhage after manual removal of retained placenta after vaginal birth):
- Blood products
- Hysterectomy