In normal circumstances, the trophoblast stops invading the uterus when Nitabuch’s layer is reached in the decidua. In cases of accreta, the trophoblast invades the myometrium due to a deficient or damaged Nitabuch’s layer. Placenta accreta occurs within a spectrum of disorders now referred to as ‘Placenta Accreta Spectrum’ (formerly ‘Morbidly Adherent Placenta’)

• Placenta Accreta: trophoblasts attach to the myometrium without intervening decidua
• Placenta Increta: trophoblasts invade through the myometrium
• Placenta Percreta: trophoblasts move through the myometrium and invade beyond the serosa and into surrounding tissues

Clinical Actions:

• It is advisable to refer women with clinical or ultrasound risk factors for placenta accreta to a center of excellence for evaluation, confirmation and delivery (Grade 1B – Strong recommendation – Moderate quality evidence)
  • Arrange for delivery at a level III or IV center with experience if possible
• Optimal timing of delivery
  • Without bleeding or contractions can have a planned cesarean delivery at 34w0d – 35w6d (Grade 1A – Strong recommendation – High quality evidence)
• Corticosteroids
  • Administer corticosteroids to all women with suspected accreta if (SMFM recommendation Grade 1A)
    • Delivery expected within 7 days and meets gestational age criteria
    • Antenatal corticosteroids have not previously been administered
  • Do not delay delivery in the setting of active hemorrhage for the purpose of administering antenatal corticosteroids (SMFM recommendation Grade 1B)
• Hospitalization of women with preterm accreta and labor or bleeding is reasonable

Management

• In the setting of hemorrhage, the following blood product ratio range is recommended based on data from other surgical specialties (Grade 1A)
  • Packed RBC:FFP:Platelet = 1:1:1 to 1:2:4
• High Risk management can be found in the ‘SMFM Guidelines’ and ‘Obstetric Care Consensus’  (see ‘Learn More – Primary Sources’ below)
• Uterine preservation
  • Conservative management: Removal of placenta or uteroplacental tissue and no hysterectomy
    • Focal placental adherence
    • Followed by repair of uterine defect
    • Data limited
  • Expectant management: Placenta left in situ
    • More extensive adherence
    • Data limited
  • ACOG/SMFM obstetric care consensus (2018) states

Conservative management or expectant management should be considered only for carefully selected cases of Placenta Accreta Spectrum after detailed counseling about the risks, uncertain benefits, and efficacy and should be considered investigational (Grade 2C – Weak recommendation – Low quality evidence)

Synopsis:

The incidence of placenta accreta has been increasing from 0.8/1000 in the 1980’s to 3/1000 deliveries. The risk increases with the increasing number of cesarean deliveries. This is especially true for women with placenta previa and prior cesarean sections. Mortality may be as high as 6 to 7%. Maternal complications are primarily the result of massive hemorrhage which can lead to DIC, multi-organ failure, hysterectomy, thromboembolism and death. Neonatal complications are the result of prematurity. The average gestational age at delivery of a pregnancy with Accreta is 34-36 weeks.

Key Points:

If previa is present

• 3% risk of accreta with the 1st cesarean section
• 11% risk of accreta at the 2nd cesarean section
• 40% risk of accreta at the 3rd cesarean section
• 61% risk of accreta at the 4th cesarean section
• 67% risk of accreta at the 5th cesarean section

Risk factors

• Prior cesarean section
• Uterine curettage
• Prior myomectomy
• Placenta previa
• Short inter-pregnancy interval
• IVF
• Multiparity
• Prior pelvic radiation
• Endometrial ablation
• Maternal smoking

The mainstay of antenatal diagnosis is ultrasound

Note: Absence of ultrasound findings does not mean the patient does not have accreta | Clinical risk factors should be weighted equally compared to sonographic findings (Grade 1A)

• First trimester findings include
  • Cesarean scar pregnancy (risk may approach 100% if pregnancy allowed to continue)
  • Gestational sac implanted in the lower uterine segment
  • Irregular vascular spaces in the placental bed
  • Loss of retroplacental-myometrial zone

• Second and third trimester findings include
  • placenta previa (present in 80% of accreta)
  • loss of retroplacental-myometrial hypoechoic zone
  • multiple vascular lacunae
  • placental villi extension into the myometrium and beyond
  • interruption of the uterine serosal/ bladder interface
  • decreased retroplacental myometrial thickness (<1mm)

Role of MRI

• MRI has sensitivities (75%-100%) and specificities (65%-100%) approaching that of ultrasound, but has not been shown to improve the diagnostic accuracy of accreta compared to ultrasound (Grade 1B)

Learn More – Primary Sources:

ACOG/SMFM Obstetric Care Consensus: Placenta Accreta Spectrum

Society for Maternal-Fetal Medicine (SMFM) Consult Series #44: management of bleeding in the late preterm period

SMFM Publications & Guidelines: Placenta Accreta

Abnormal Placentation: Placenta Previa, Vasa Previa, and Placenta Accreta

Related ObG Topics:

Placenta previa – nomenclature, diagnosis and clinical management

Vasa Previa: Diagnosis and Management

Does MRI Help or Hurt When Making a Diagnosis of Placenta Accreta?

Antepartum Corticosteroids – When to Administer?

Ultrasound for Previa Accreta in Women with Prior C-Section

Does Intra-Aortic Balloon Improve Outcomes during Surgery for Adherent Placenta