Placenta accreta

Overview: We sought to review the risks of placenta accreta, increta, and percreta, and provide guidance regarding interventions to improve maternal outcomes when abnormal placental implantation occurs.

Diagnosis/definition: Placenta accreta occurs when all or part of the placenta attaches abnormally to the myometrium. Three grades of abnormal placental attachment are defined according to the depth of invasion:

• Accreta: Chorionic villi attach to the myometrium, rather than being restricted within the decidua basalis.
• Increta: Chorionic villi invade into the myometrium.
• Percreta: Chorionic villi invade through the myometrium.

In this document, the general term “placenta accreta” will refer to all 3 grades of abnormal placental attachment (placenta accreta, increta, and percreta) unless otherwise specified.

Epidemiology/Incidence: The reported incidence of placenta accreta has increased from approximately 0.8 per 1000 deliveries in the 1980s to 3 per 1000 deliveries in the past decade. 
Risk factors/associations: An important risk factor for placenta accreta is placenta previa in the presence of a uterine scar. Placenta previa is an independent risk factor for placenta accreta. The frequency of placenta accreta according to number of cesarean deliveries and presence or absence of placenta previa is shown in (Table 1). Additional reported risk factors for placenta accreta include maternal age and multiparity, other prior uterine surgery, prior uterine curettage, uterine irradiation,endometrial ablation, Asherman syndrome, uterine leiomyomata, uterine anomalies, hypertensive disorders of pregnancy, and smoking.

Complications: Examples include: (i) damage to local organs (eg, bowel, bladder, ureters) andneurovascular structures in the retroperitoneum and lateral pelvic sidewalls from placental implantation and its removal; (ii) postoperative bleeding requiringrepeated surgery; (iii) amniotic fluid embolism; (iv) complications (eg, dilutional coagulopathy, consumptive coagulopathy, acute transfusion reactions, transfusion-associated lung injury, acute respiratory distress syndrome, and electrolyte abnormalities) from transfusion of large volumes of blood products, crystalloid, and other volume expanders; and (v) postoperative thromboembolism, infection, multisystem organ failure, and maternal death. The exact incidence of maternal mortality related to placenta accreta and its complications is unknown, but has been reported to be as high as 6-7% in case series and surveys.

Management:
Screening/Work-up: When the antepartum diagnosis of placenta accreta is made, it is usually based on ultrasound findings in the second or third trimester. Sonographic findings that may be suggestive of placenta accreta are summarized in Table 2 and some common features are demonstrated in Figure 1. At present, no analyte is considered a necessary component in the workup in women with suspected accreta. Women with a placenta previa overlying a uterine scar should be evaluated for the potential diagnosis of placenta accreta. Women with a placenta previa or “low-lying placenta” overlying a uterine scar early in pregnancy should undergo follow-up imaging in the third trimester with attention to the potential presence of placenta accreta. While obstetric ultrasound is the primary tool for the diagnosis of placenta accreta, magnetic resonance imaging can be helpful if ultrasound is inconclusive or if placenta percreta is suspected.
Delivery: A pre-operative checklist is suggested in Table 3. When the diagnosis of placenta accreta is suspected antenatally, delivery should be scheduled in an institution with appropriate expertise and facilities including the ability to manage severe hemorrhage. Because the availability of adequate facilities and resources to manage severe hemorrhage at delivery is important, scheduled late preterm delivery (34 0/7 – 35 6/7weeks) is acceptable when placenta accreta is suspected antenatally. The potential need for hysterectomy should be anticipated when the diagnosis of placenta accreta is made. Hysterectomy with the placenta left in situ after delivery of the fetus should be considered.o Intraoperatively, attention should be paid to abdominal and vaginal blood loss. Early blood product replacement, with consideration of volume expansion, increasing oxygen-carrying capacity, and normalization of coagulation factors, can reduce perioperative complications.o When surgery for placenta accreta is planned, the potential need for postoperative intensive care unit admission should be considered. Arterial embolization is appropriate for the hemodynamically stable patient with persistent intrapelvic bleeding despite surgical measures. However, transport from the operating room to accomplish this intervention is not generally suitable for the hemodynamically unstable patient.

Last Reaffirmed: Feb 1, 2013