Placenta Accreta


Continuing Education Activity

Placenta accreta spectrum (PAS) disorders are considered to be iatrogenic conditions. They are more common in women with previous cesarean deliveries. The incidence and the prevalence of PAS disorders will continue to rise all over the world due to the increasing rate of cesarean deliveries. PAS disorders are associated with an increased risk of maternal morbidity and maternal mortality. This activity reviews the evaluation and management of women with PAS disorders and highlights the role of the interprofessional team in the care of patients with this condition.

Objectives:

  • Describe the pathophysiology of the placenta accreta spectrum disorders.
  • Review clinical findings associated with placenta accreta spectrum (PAS) disorders.
  • Summarize the treatment options of placenta accreta spectrum disorders.
  • Explain the importance of collaboration and coordination among the interprofessional team members to enhance the care of patients with placenta accreta spectrum disorders.

Introduction

In a normal pregnancy, the placenta anchors to decidualized endometrium.[1] The abnormal invasion of placental trophoblasts into the uterine myometrium is referred to as placenta accreta. It is considered to be a spectrum of disorders, encompassing placenta accreta, placenta increta, and placenta percreta, based on the degree of myometrial invasion. Placenta accreta spectrum (PAS) disorders are associated with increased maternal morbidity and mortality. Therefore, these patients should be cared for by an interprofessional team.[2] 

The FIGO (International Federation of Gynecology and Obstetrics) proposed a nomenclature grading system under the umbrella diagnosis of placenta accreta spectrum disorders (PAS), that replaced the old categorical terminology (placenta accreta, increta, and percreta).[3]

Etiology

Placenta accreta spectrum (PAS) disorders are most commonly associated with a history of a previous cesarean section. This is likely due to the abnormal placentation secondary to the loss of decidua in the cesarean section scar. However, there are other risk factors associated with placenta accreta, including advanced maternal age and multiparity. Placenta previa is present in approximately 80 percent of placenta accreta cases. Placenta accreta has also been linked to other types of uterine surgery, such as myomectomy, uterine curettage, hysteroscopic surgery, prior endometrial ablation, uterine embolization, and pelvic irradiation.[1]

Epidemiology

The incidence of placenta accreta has increased from 1 in 30,000 pregnancies in the 1960s to 1 in 533 pregnancies in the 2000s.[4] One study quotes the current incidence as high as 1 in 272.[5] As previously noted, prior cesarean delivery is a risk factor for placenta accreta, so the rise in placenta accreta incidence over the past decades is reflective of the rise in cesarean deliveries. Furthermore, it has been established that an increased number of prior cesarean sections increases the risk of placenta accreta. Approximately 6.7% of patients with five prior c-sections were noted to have placenta accreta, compared to 0.3% of patients with one prior c-section.[6]

Pathophysiology

In typical placentation, trophoblast invasion stops at the spongiosus layer of the decidua. There are many theories as to why placenta accreta may occur. One leading theory is that in patients with prior uterine surgeries, the spongiosus layer of the decidualized endometrium may not be present. Therefore, the typical stop signal is absent. Furthermore, cytotrophoblasts must also reach the spiral arterioles before differentiation into placenta tissue may occur. However, uterine scars have a relative lack of vasculature. It is important to note that, although rare, placenta accreta can occur in nulliparous women and women without prior uterine surgery.[2]

Histopathology

The histology of PAS disorders reveals placental invasion into the uterine myometrium. In the case of placenta percreta, it may also invade into the serosa or other organs. There is also an increased rate of trophoblastic inclusions compared to normal placentation. These inclusions are characterized by an inner layer of syncytiotrophoblasts contained within an outer layer of cytotrophoblasts. They are most commonly associated with molar pregnancies and chromosomal aneuploidies. However, one group documented their presence in 40 percent of placenta accreta specimens, compared to 2.4 percent of controls.[7]

History and Physical

It is important to identify risk factors for placenta accreta, including parity and prior uterine surgeries, at the initial obstetric visit. Rarely, patients will have urinary and bowel symptoms in cases of placental percreta involving those organs. Typically, diagnosis is reliant on imaging.

Evaluation

Antenatal diagnosis of placenta accreta is typically made by ultrasound. Ultrasound will reveal placenta previa. Furthermore, it is possible to visualize other abnormalities, including loss of hypoechoic division between the placenta and myometrium, increased vasculature, myometrial thinning, and extension of the placenta into serosa or bladder.[2] 

Color Doppler may reveal lacunae with turbulent blood flow. Notably, the sensitivity and specificity of ultrasonography appear to be highly variable. Individual studies of ultrasound diagnosis of accreta report a large range of sensitivities and specificities.[8][9][10] However, a systemic review and meta-analysis of ultrasound demonstrated a sensitivity of 90.8% and a specificity of 96.9%. Important factors in the diagnosis are the presence of lacunae and the loss of hypoechoic retroplacental space.[11] Additionally, the presence of previa increases the rate of diagnosis from 6.9% to 72.3%.[12] The experience of the ultrasonographer and clinician must also be taken into account.[2]

Magnetic resonance imaging (MRI) has also been investigated for the diagnosis of placenta accreta. A systemic review of the MRI-based diagnosis of placenta accreta demonstrated a specificity of 84.0% and a sensitivity of 94.4%.[13] While at first glance, this may interest some providers, it is worth noting that selection bias is difficult to avoid in these studies. Patients are typically chosen for MRI when their ultrasound findings are inconclusive. Furthermore, it is important to consider the cost and the lack of availability of MRI. At this time, ultrasound remains the modality of choice for diagnosis.[2]

Treatment / Management

Placenta accreta spectrum is best managed when it has been diagnosed antenatally. Many steps can be undertaken to minimize risks. The American College of Obstetricians and Gynecologists (ACOG) has recommended delivery between 34 0/7 – 35 6/7 weeks of gestation via cesarean hysterectomy to optimize neonatal maturity and minimize the risk of maternal bleeding.[2] Before delivery, there should be a consideration for transfer to a (PACE) Placenta Accreta Center of Excellence or a level three or four center for delivery. Outcomes have been improved by delivery at these facilities due to the availability of a large, interprofessional team. These teams should include perinatologists, pelvic surgeons, intensivists, general surgeons, urologists, and neonatologists. In patients with bleeding, consideration should be made for an early transfer to be near an appropriate facility. Furthermore, the patient’s hemoglobin level should be optimized before delivery, and there should be coordination with the blood bank to ensure supplies if a massive transfusion should be needed.[2]

Cesarean sections are typically performed in a manner that allows for easy conversion to hysterectomy. This includes dorsal lithotomy positioning and a vertical skin incision. The uterine incision should be made in a manner that would avoid the placenta. After the delivery of the neonate, if the placenta does not deliver spontaneously, the current recommendation is to leave the placenta, close the hysterotomy, and perform a hysterectomy. This approach minimizes the risk of hemorrhage. Often, supracervical hysterectomies are not possible due to bleeding. The surgeon may also need to consider cystotomy to separate the placental tissue.

Close monitoring of hemodynamic status and blood loss should be performed. ACOG recommends monitoring blood loss, hemoglobin, electrolytes, blood gas, and coagulation factors to determine the need for transfusion objectively. Most often, massive transfusion protocols involve a 1 to 1 to 1 ratio of packed red blood cells, fresh frozen plasma, and platelets. However, patients may also consider autologous donation ahead of the procedure.[2] 1g IV tranexamic acid, an antifibrinolytic therapy, can be considered within the first three hours of delivery. It has been shown to reduce maternal death due to hemorrhage without an increase in adverse effects.[14] 

After the procedure, ACOG recommends admission to the intensive care unit to closely monitor for signs of bleeding, hypoperfusion, and fluid overload from resuscitation.[2] Of note, some providers also offer delayed hysterectomy. In this practice, the placenta is left in situ, and the hysterectomy is performed at a later time. In the limited number of reported cases, it has been shown to decrease blood loss and decrease the need for transfusion. However, this is still considered to be investigational.[15]

In patients with unknown placenta accreta, there are typically two routes of management. First, if the accreta is discovered before hysterotomy, the procedure should be paused until the appropriate help has arrived, blood products have been ordered, and the anesthesia team has been made aware. In the second route, the accreta is discovered when the placenta does not deliver with typical maneuvers. In this scenario, the surgeon should proceed with hysterectomy, as outlined previously. If a hysterectomy is not possible at that facility, then a transfer should be considered. The surgeon will need to pack the abdomen and consider transfusion and tranexamic acid.[2]

For those wishing to preserve future fertility, conservative management or expectant management can also be considered. In conservative management, the placenta or uteroplacental tissue is removed without the removal of the uterus. This route is more successful in patients with small defects, which can easily be surgically removed or over-sewn.[2] There are also reports involving the successful use of Bakri balloons.[16] 

Expectant management is an area of investigation for women wishing to preserve fertility, but have an extensive accreta. This route involves leaving the placenta in situ, with or without adjunctive methotrexate use. In one study, 78 percent of patients were able to avoid hysterectomy.[17] In some cases, the placenta has been removed using hysteroscopic resection. Regardless of the route of fertility conservation, it is important to counsel the patient extensively on potential risks, including the risk of hemorrhage, hysterectomy, and accreta recurrence (15-30 percent) in future pregnancies.[2]

Differential Diagnosis

While they are all on the placenta accreta spectrum, it is essential to distinguish between placenta accreta, increta, and percreta. The involvement of other organs is especially important to ascertain ahead of the planned surgery. Additionally, differentiating between placenta previa and placenta previa with accreta allows for the correct preparation and counseling. As previously mentioned, ultrasound is the currently recommended imaging modality of choice. However, magnetic resonance imaging (MRI) may be considered to determine the degree of invasion.[2]

Prognosis

Prognosis is better for patients who have placenta accreta without placenta previa. Placenta accreta with previa has a higher risk of hemorrhage and is more likely to undergo a hysterectomy, both of which contribute to morbidity.[12] Patients who have placenta percreta are at an increased risk of complications compared to placenta accreta and increta. These patients have a statistically significant higher rate of renal tract injuries, intensive care unit (ICU) admissions and the need for additional blood products.[18]

Complications

The most common maternal complication associated with the placenta accreta spectrum is postpartum hemorrhage. This can be associated with intraoperative hypoperfusion, transfusion, post-resuscitation fluid overload, and disseminated intravascular coagulopathy (DIC). Transfusion was required in 80 percent of cases, and DIC occurred in 28 percent of cases in one study.[19] Hemorrhage is best reduced if the placenta is left in situ after fetal delivery, as noted previously; however, it is often not avoidable. As mentioned, patients should be monitored in the intensive care unit (ICU) following surgery to observe for hemorrhage-related complications carefully.

Another major complication is damage to nearby structures. Inadvertent or intentional cystotomy can occur during the procedure. Most commonly, the placenta is anterior and, therefore, may invade the bladder. In this case, cystotomy may be necessary to separate the placental tissue. Ureteral injury may also occur due to the technical difficulty of a cesarean hysterectomy. Patients should be adequately counseled on these complications.

As with most obstetrical pathologies, the neonate is also affected. Neonatal morbidity and mortality result from preterm birth. Furthermore, maternal hemorrhage can result in decreased fetal oxygenation.[1]

Deterrence and Patient Education

As mentioned previously, increasing the number of previous cesarean sections will also increase the risk of placenta accreta. Patients should be counseled on this risk when discussing repeat cesarean sections and birth control options. If a placenta accreta spectrum disorder is diagnosed antenatally, then the many possible complications should be reviewed. Patients should be consented for transfusion and informed of possible admission to the intensive care unit. Furthermore, future fertility must be discussed. If a patient desires fertility-sparing options, they should be counseled on failure rate and possible re-operation.[2]

Pearls and Other Issues

Placenta accreta spectrum disorders encompass various degrees of placental invasion into the uterine myometrium. A history of cesarean section or other uterine surgery is the most common risk factor for placenta accreta. Antepartum diagnosis of placenta accreta is preferable so that the patient can deliver at the appropriate time and the proper location. The current recommendation is for delivery between 34 0/7 to 35 6/7 weeks via cesarean hysterectomy. There are fertility-sparing options, but patients must be counseled thoroughly before selecting this option. This procedure should occur at a facility with an adequate blood bank, and that would allow for an interprofessional team approach.

Enhancing Healthcare Team Outcomes

Placenta accreta spectrum (PAS) disorders are considered to be a very challenging obstetric condition that mandates the coordination and collaboration among the members of the interprofessional team. These teams should include perinatologists to assist with diagnosis, intensivists for postpartum and post-surgical care in the intensive care unit, and neonatologists to care for the preterm infant. Additionally, the provider performing the surgery should be comfortable performing cesarean hysterectomies and have access to surgeons who can assist in the case of percreta or damage to surrounding organs. This may include gynecologic oncologists, general surgeons, or urologists. A well-equipped blood bank should be available for the possibility of a massive transfusion.

The presence of an interprofessional approach has been shown to decrease reoperation rates, intensive care admissions, and large-volume blood transfusion rates. The nurse plays a paramount role in the evaluation and management of women with PAS disorders. The nurse should monitor and update the clinician regarding vital signs and fetal cardiotocographs. The nurse should assist the obstetric provider in educating women with PAS disorders and their families about the nature of their condition and any anticipated challenges during their antenatal, natal, and postnatal periods. Patient education is key to the successful management of women with PAS disorders, and women should be provided with patient information leaflets that are easy to understand.

Women should be given adequate time to discuss decisions with their families and friends. Fertility preservation options should be carefully discussed with women with PAS disorders. Women should be encouraged to express their wishes about preserving fertility with a thorough discussion of risks and benefits. Throughout these discussions and the patient's antenatal and postpartum course, members of the interprofessional team should coordinate to optimize maternal and fetal outcomes. [Level 5]


Article Details

Article Author

Alexa Shepherd

Article Editor:

Heba Mahdy

Updated:

2/25/2021 5:46:07 PM

PubMed Link:

Placenta Accreta

References

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