Learning Objectives:After participating in this continuing education activity, the provider should be better able to:

1. Describe risk factors for placenta accreta spectrum disease.

2. Initiate intrapartum management strategies for placenta accreta spectrum that will optimize patient outcomes.

3. Counsel patients regarding the risks and benefits of both definitive and uterine-conserving management of placenta accreta spectrum.

Placenta accreta spectrum (PAS) is a highly morbid and potentially fatal complication of pregnancy. The frequency of this condition has increased eightfold since 1970.1 The incidence of placenta accreta is now estimated at 1 in 272 to 533 deliveries in the United States.2-4 There is a 40% risk of needing massive transfusion (>10 units of packed red blood cells) and a 7% mortality rate associated with PAS.5 PAS is also the most common reason to perform both peripartum and cesarean hysterectomy.1,5 As such, obstetrician gynecologists must be able to identify risk factors for PAS, be familiar with its associated morbidities, and implement strategies for PAS recognition, triage, and appropriate management to achieve optimal patient outcomes.

Definition of Placenta Accreta Spectrum

PAS encompasses 3 different subtypes dependent on depth of trophoblast invasion into the myometrial wall. All subtypes involve the absence of placental decidua basalis. Placenta accreta occurs when trophoblastic villi are attached to the myometrial surface. Placenta increta occurs when villi invade into the myometrium. The villi in placenta percreta reach the level of the uterine serosa or penetrate through it.1,6

Incidence and Risk Factors

As noted earlier, current estimates of PAS incidence vary from 1 in 272 to 533 deliveries in the United States.2-4 The frequency of PAS in 1970 was estimated at 1 in 4000 deliveries with increase to 1 in 2500 deliveries in the 1980s and further increase to current levels thereafter.1 The dramatic increase in the incidence of PAS is strongly associated with the increased rates of cesarean delivery, and there is a clear relationship between the number of prior cesarean deliveries undergone by a woman and the subsequent diagnosis of PAS.7 Other risk factors for PAS include uterine instrumentation of any kind (myomectomy, uterine curettage, myomectomy, and endometrial ablation), uterine artery embolization, manual extraction of the placenta, and in vitro fertilization pregnancies.8,9 The presence of placenta previa with a history of prior cesarean delivery is a particularly strong risk factor for PAS and increases with the number of prior cesarean delivery (3%, 11%, 40%, 61%, and 67% for the first through fifth prior cesarean deliveries, respectively).7,10 PAS occurs extremely rarely in women with no known risk factors, although conditions thought to contribute to PAS include submucosal fibroids, adenomyosis, and bicornuate uterus.6

Antenatal Diagnosis

Given the potential for morbidity and mortality associated with PAS, antenatal diagnosis of PAS is key in planning safe deliveries for women with this condition. Antenatal diagnosis of PAS is associated with a higher rate of antenatal corticosteroid administration and a lower volume of intraoperative blood loss.11 Ultrasound is the primary diagnostic imaging modality for PAS. Ultrasonographic features of PAS include placental lakes, loss of the so-called "clear space" between placenta and myometrium, abnormal bladder-uterine interface, reduced myometrial thickness underlying the placenta (<1 mm), and gross invasion of the placenta into the myometrial wall, uterine serosa, or bladder.3 Among these, the presence of placental lakes is the most sensitive ultrasonographic sign of PAS.3,12

Although ultrasound is a useful tool to evaluate for presence of PAS, it is not perfect. Ultrasound sensitivity in detecting PAS ranges from 53% to 74%, with specificity ranging from 70% to 94%.12 Suspected PAS cases can be further evaluated with MRI to assess for extensive invasion and develop a surgical plan. However, MRI is not routinely used for screening patients for abnormal placentation, and is considerably more expensive than obstetric ultrasound.1,3

Delivery Planning

In a joint statement, the American College of Obstetricians and Gynecologists (ACOG), the Society of Gynecologic Oncology, and the Society for Maternal-Fetal Medicine recommend that patients with suspected PAS be evaluated and managed at tertiary care facilities with multidisciplinary accreta teams due to decreased maternal morbidity in the delivery setting.3 Management of PAS by dedicated multidisciplinary teams is associated with lower composite scores of morbidity, lower incidence of massive transfusion, and fewer reoperations for bleeding complications.5,13 Management of obstetric hemorrhage in high-volume tertiary care settings is also associated with lower maternal mortality.14

Emergent delivery and cesarean hysterectomy for patients with PAS are associated with increased blood loss and need for transfusion, higher volume of blood transfusion, and need for intensive care admission.11,15,16 To minimize the maternal morbidity of emergent delivery and balance the neonatal morbidity of prematurity, the recommended gestational age for delivery is 34 to 35 weeks in pregnancy affected by PAS.3,17 In light of this, antenatal corticosteroids should be administered in anticipation of preterm delivery to promote fetal lung maturation.3 Amniocentesis to confirm fetal lung maturity is not indicated at this gestational age, given the indication for delivery is for maternal concerns.1,3

Preoperative Planning

As mentioned earlier, multidisciplinary teams dedicated to the care of patients with PAS have been shown to reduce maternal morbidity. ACOG recommends that these teams include maternal-fetal medicine physicians, pelvic surgeons with appropriate expertise, neonatologists, and anesthesiologists.3 Other consultants should be included as the clinical scenario dictates (eg, urologists). Close coordination with the blood bank is also strongly recommended, as the risk of transfusion is high.3 The evidence for preoperative placement of ureteral stents is mixed; ACOG recommends an individualized approach for patients with suspected bladder involvement.3 Similarly, the value of preoperative intravascular catheterization or balloon placement is unclear; ACOG recommends against routine use of these measures.3

Intraoperative Management

Given the risk of hemorrhage, adequate vascular access should be obtained preoperatively (large-bore venous access, possible central venous access).1 Blood products sufficient to support a patient through a massive hemorrhage should be available at the time of surgical start.1 Having autologous red cell salvage equipment in the operating room should be considered.1,3,18 Capabilities for rapid laboratory assessment of the patient's blood counts and clotting status should be available.1 Perioperative antibiotics should be administered and appropriately redosed based on standard guidelines based on blood loss and length of procedure.19 Lower extremity sequential compression devices should be used as prophylaxis against venous thromboembolism.1 Dorsal lithotomy positioning with a left lateral tilt should be considered in case access to the vagina or bladder is required.3 Equipment needed to warm the patient to prevent temperature-associated coagulopathy should be available.1 There is no standard anesthetic approach for surgical management of PAS, and the decision to use regional or general anesthesia should be determined by the anesthesiology team.

In general, the recommended surgical management of PAS is planned cesarean hysterectomy.1,3 In patients who strongly desire uterine conservation, alternate approaches can be undertaken after appropriate preoperative counseling. These approaches will be discussed separately.

Adequate surgical exposure is paramount; vertical midline, Maylard, and Cherney incisions should be considered.1,3,18 The hysterotomy incision should be made in a manner that avoids disrupting the placenta to extent possible.1,3 Following delivery and after ensuring that the placenta will not deliver spontaneously, most clinicians then quickly close the hysterotomy incision and proceed with hysterectomy.3 Total hysterectomy is preferred to supracervical hysterectomy but may not always be surgically feasible.18 Forcible attempts at removal of the placenta should be avoided, as they are associated with greater risk of hemorrhage and higher overall morbidity.3,11,15 Cystoscopy can be considered on a case-by-case basis, with the knowledge that peripartum hysterectomy carries a risk of bladder injury 9 times higher and a risk of ureteral injury 5 times higher than nonobstetric hysterectomy.20 Surgical techniques for refractory hemorrhage include hypogastric artery ligation, arterial embolization performed by interventional radiology if patient stability allows, manual aortic compression or balloon tamponade, and pelvic packing.3

In the event of hemorrhage, blood products should be given in a fixed ratio (typically 1:1:1 for packed red blood cells, fresh frozen plasma, and platelets, respectively) consistent with a massive transfusion protocol.3 Tranexamic acid administration to combat fibrinolysis can be considered either on an as-needed or a prophylactic basis.3,18 Hypofibrinogenemia with fibrinogen levels less than 200 mg/dL is a significant risk factor for postpartum hemorrhage and can be corrected with administration of cryoprecipitate or fibrinogen concentrates.3

Given that many patients with PAS are undiagnosed before their delivery, it is not always possible to mobilize a multidisciplinary team or plan for care of the patient in a tertiary setting. Thus, it is critical that all obstetricians be knowledgeable regarding the management of PAS.

Alternate Management Approaches

Alternate management strategies for PAS can be broadly divided into categories of expectant management, uterine preservation, and delayed planned hysterectomy.3,18 Expectant management entails leaving the placenta in situ.3,21 In expectant management, the umbilical cord is ligated proximally near the cord insert, and the placenta is left undisturbed. Case series of this approach show need for eventual hysterectomy in 22% to 42% of expectantly managed patients.3,21 In the largest case series of expectant management to date, placental resorption occurred in 75% of cases at a median of 13.5 weeks from delivery.22 Hysteroscopic resection of placental tissue or uterine curettage was required in 29% of cases in this series.22 The most common causes for hysterectomy in this series after attempted expectant management were hemorrhage (early or delayed) and maternal sepsis.22

Six percent of patients in this series experienced significant morbidity, such as sepsis, septic shock, venous thromboembolism, uterine necrosis, and fistula formation.22 Due to the length of time needed for placental resorption, this approach requires extensive follow-up and should not be offered to patients unable to comply with these requirements.

Uterine preservation is a conservative management strategy in which the placenta is removed and uterus is left in situ.3,21 As stated earlier, the risk of attempted placental removal in PAS is massive hemorrhage, and the forcible removal of the placenta should always be avoided.21 However, manual removal, curettage, or surgical excision of the placenta is possible in patients with limited or focal areas of placental adherence. Hemorrhage management strategies in those patients include placement of an intrauterine balloon for tamponade and resection of the adherent area with subsequent closure.3 Evidence describing the effectiveness of these approaches is limited.3

Delayed planned hysterectomy is a nonconservative management option for patients with highly invasive PAS.18 After cesarean delivery, the umbilical cord is ligated proximally, and the placenta is left in situ, just as in expectant management of PAS. The goal of delay is to allow time for some placental resorption, hopefully decreasing the morbidity of eventual hysterectomy. After close monitoring, interval hysterectomy is performed 3 to 12 weeks after delivery.18 Once again, data for this approach are limited.

Methotrexate is currently not recommended as a conservative management strategy for PAS. There are no data demonstrating efficacy of this approach in producing placental resorption, and methotrexate has known renal and hematologic risks. Furthermore, methotrexate is contraindicated in breastfeeding.3,21

Once again, the standard of care for patients with PAS is peripartum hysterectomy. Alternate approaches should only be offered to selected patients after extensive counseling about the risks of conservative management, including possible need for eventual and perhaps emergent hysterectomy, delayed hemorrhage, need for additional surgical procedures (including uterine curettage and hysteroscopic resection of placenta), and possibility of significant morbidity related to conservative measures (eg, infection in expectant management).3 All women who undergo conservative management should be informed that likelihood of recurrent PAS in a future pregnancy is high.21

Conclusion

PAS is an increasingly frequent disorder of pregnancy with the potential for severe morbidity and also maternal mortality, largely related to the risk of massive obstetric hemorrhage. The primary risk factor for PAS is a history of cesarean delivery. Patients with risk factors should be carefully screened for PAS during their prenatal care with obstetric ultrasound; MRI can be used as necessary as an adjunctive imaging modality. Whenever possible, women with known PAS should undergo planned cesarean hysterectomy at a tertiary care center where an experienced PAS team is available. Alternative management strategies should only be undertaken in select patients after extensive counseling on the pertinent risks.

Practice Pearls

* Patients with major risk factors for PAS should be carefully screened by obstetric ultrasound.

* Patients with suspicion for PAS on ultrasound may undergo MRI if necessary to make or confirm the diagnosis.

* Patients with PAS should be referred to tertiary care centers with PAS expertise for delivery whenever possible.

* Delivery for patients with PAS should be planned for 34 to 35 weeks' gestational age.

* Antenatal corticosteroids should be given to patients with PAS in anticipation of preterm delivery.

* PAS care teams should include maternal-fetal medicine, an expert pelvic surgeon, anesthesiology, neonatology, and any other services needed based on clinical situation.

* Forcible attempts to remove the placenta in known PAS cases should be avoided.

* The standard approach for PAS management is peripartum hysterectomy.

* Appropriate blood products should be available for every PAS surgical case.

* Alternative PAS management strategies should only be offered to select candidates after thorough preoperative counseling.

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