Placenta Accreta Spectrum (Accreta, Increta, Percreta)

Summary

Placenta accreta spectrum is abnormal placental invasion into the uterus, most often linked to prior cesarean or placenta previa. It may cause failure of placental separation and severe hemorrhage, with management usually by planned cesarean hysterectomy.

Definition

Placenta accreta spectrum (PAS) refers to abnormal placental adherence and invasion into the uterine wall, representing a spectrum of disorders classified according to the depth of trophoblastic invasion. Normally, placental villi penetrate only the superficial decidua basalis. When this boundary is breached, varying degrees of abnormal invasion occur:

• Placenta accreta: Villi attach abnormally to the myometrium without invasion. This is the most common type, accounting for ~80% of cases.

• Placenta increta: Villi invades into the myometrium but not through it (~15% of cases).

• Placenta percreta: Villi penetrate through the myometrium and serosa, sometimes invading adjacent organs such as the bladder (~5% of cases).
  
  

Risk Factors

Placenta accreta spectrum is strongly associated with uterine scarring and abnormal placental implantation. Major risk factors include:

• Previous cesarean section (risk increases with number of cesareans)

• Placenta previa (particularly over a uterine scar)

• Prior uterine surgery or curettage

• Advanced maternal age (>35 years)

• Multiparity, with risk increasing with each pregnancy
  

Clinical Features

Placenta accreta spectrum is often asymptomatic during pregnancy and typically detected incidentally on antenatal imaging. Key features include:

• Ultrasound findings: Loss of the normal placental–myometrial interface, placental lacunae, and increased vascularity.

• Third-trimester vaginal bleeding (occasionally).

• Failure of placental separation after delivery, often accompanied by massive postpartum hemorrhage.

• Severe hemorrhage at delivery, with an average blood loss of 3,000–5,000 mL.
  
  

Diagnosis

• Ultrasound is the primary diagnostic tool; MRI may be used for further evaluation in complex cases.

• Many cases remain undiagnosed until delivery, when placental separation fails and hemorrhage ensues.

Management

• Planned cesarean hysterectomy is the standard treatment for antenatally diagnosed cases, performed at a tertiary center with multidisciplinary support.

• If undiagnosed until delivery, management involves urgent resuscitation, hemorrhage control, and hysterectomy.

• Conservative management (leaving the placenta in situ) may be considered in select cases, but carries risks of infection and delayed hemorrhage.