Placenta accreta spectrum is one of the most morbid conditions obstetricians will encounter. The incidence has dramatically increased in the last 20 years. The major contributing factor to this is believed to be the increase in the rate of cesarean delivery. Despite the increased incidence of placenta accreta, most obstetricians have personally managed only a small number of women with placenta accreta. The condition poses dramatic risk for massive hemorrhage and associated complication such as consumption coagulopathy, multisystem organ failure, and death. In addition, there is an increased risk for surgical complications such as injury to bladder, ureters, and bowel and the need for reoperation. Most women require blood transfusion, often in large quantities, and many require admission to an intensive care unit. As a result of indicated, often emergent preterm delivery, many babies require admission to a neonatal care intensive care unit. Outcomes are improved when delivery is accomplished in centers with multidisciplinary expertise and experience in the care of placenta accreta. Such expertise may include maternal-fetal medicine, gynecologic surgery, gynecologic oncology, vascular, trauma and urologic surgery, transfusion medicine, intensivists, neonatologists, interventional radiologists, anesthesiologists, specialized nursing staff, and ancillary personnel. This article highlights the desired features for a center of excellence in placenta accreta, and which patients should be referred for evaluation and/or delivery in such centers.
Placenta accreta occurs when the placenta abnormally adheres to underlying myometrium, often where there is an absence of decidua basalis. Depending upon the depth of villous invasion, abnormal placental attachment is defined as placenta accreta, increta, and percreta. This article, however, will use the term “accreta” to refer to the entire spectrum of an abnormally adherent placenta. The condition can lead to massive hemorrhage and associated morbidity such as multisystem organ failure, acute respiratory distress syndrome, disseminated intravascular coagulation, and death. The frequency of placenta accreta has steadily increased over the past 40 years, increasing in the United States from <1 in 2000 in the 1980s to currently about 1 in 500 pregnancies. Placenta accreta has become the most common reason for cesarean hysterectomy in resource-rich countries. This increase is thought to be due to a concomitant rise in the rate of cesarean delivery. Indeed, prior cesarean delivery is the strongest risk factor for accreta, with an increasing risk noted with increasing numbers of prior cesareans. The risk is especially high in the setting of prior cesarean delivery and placenta previa.
The optimal management of placenta accreta remains uncertain with regard to the timing of delivery and optimal surgical approach. Indicated preterm delivery at 34-35 weeks has been proposed as a means to decrease the risk of having to perform emergency surgery, given the increasing risk of spontaneous bleeding >34 weeks’ gestation. This strategy is supported by a study of 90 cases in Texas, in which the 57 cases managed by a multidisciplinary accreta team and delivered at 34-35 weeks’ gestation had a significantly lower rate of emergency surgery. However, many cases progress to 36 weeks’ gestation without complications and the issue remains controversial.
Considerable data however, indicate decreased morbidity in cases of planned cesarean hysterectomy prior to the onset of labor, rather than emergent delivery, which is often necessitated by contractions or when clinically significant bleeding occurs. Blood loss and morbidity also are decreased if no attempt is made to remove the adherent placenta. Instead, a hysterotomy is made to avoid the placenta (often fundal), the infant is delivered, the hysterotomy is quickly sutured, and then hysterectomy is performed. In rare cases conservative management may be employed and can take 2 forms: (1) resection of that portion of the anterior uterine wall that includes the morbidly adherent placenta, followed by uterine reconstruction ; or (2) cesarean delivery without removal of the placenta, closure of the hysterotomy, and expectant management with the uterus and placenta left in situ.
Outcomes are further improved if the delivery is accomplished in a center of excellence with a multidisciplinary team with expertise and experience in the management of accreta. A study assessing 141 cases of accreta in Utah noted that women managed by a multidisciplinary team in tertiary care centers were less likely to require large volume blood transfusion, undergo a second surgical procedure, or experience composite morbidity than those receiving standard obstetric care. In fact, the same is true for all cases of massive obstetric hemorrhage, whether or not an accreta is present. Wright et al noted a decrease in maternal mortality in women with obstetric hemorrhage managed at a center of excellence compared to those cared for in traditional settings. It also is noteworthy that emergency deliveries still have reasonably good outcomes if performed in a center of excellence with a multidisciplinary team.
Despite the clear benefits of delivery in a center of excellence, referral to specialized units is underutilized. A cross-sectional survey of members of the American Congress of Obstetricians and Gynecologists revealed that only a fourth of general obstetricians referred patients with suspected accreta to centers of excellence. Thus, our purpose was to outline criteria for centers of excellence and suggested indications for referral in cases of suspected placenta accreta.
Center of excellence: placenta accreta
The key to success of an accreta center of excellence is to have coordinated, multidisciplinary teamwork between providers with the high level of skill that comes with experience in treating the condition. These criteria are outlined in Table 1 and are most often (but not exclusively) present in tertiary care centers.
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Accurate diagnosis is the first step toward this goal. Expertise and experience in pelvic imaging is paramount. Blood loss at delivery has been shown in multiple studies to be significantly reduced when accreta is diagnosed antenatally rather than intraoperatively. The field in which one subspecializes (eg, maternal-fetal medicine or radiology) is likely less important than the individual’s knowledge and experience with the antenatal diagnosis of placenta accreta. As outlined below, the primary modality for diagnosis of accreta is ultrasound. Magnetic resonance imaging (MRI) may be a useful adjunct in some cases but requires specialized equipment for pelvic imaging and experience in the assessment of accreta.
Appropriate surgical expertise is critical for an accreta center. Due to the increased size and vascularity of the uterus, the potential for severe hemorrhage is high. Particularly when the placenta is also a previa, the neovascularization that accompanies accreta is abundant deep in the pelvis, and the operative field may be obscured by the bulk of the placenta. Furthermore, the likelihood of having to remove portions of the bladder and/or ureters during the hysterectomy in placenta accreta cases is considerably higher than in simple hysterectomies in nonpregnant individuals. The specific credentials of the surgeon (eg, gynecologic oncologist, general obstetrician-gynecologist, maternal-fetal medicine specialist) are probably less important than consistent, ongoing experience with cases of placenta accreta. Most authorities believe that outcomes are improved when the surgeon is comfortable with opening and exploring the retroperitoneal space. Although not universally recommended, some data suggest less risk of ureteral injury after the placement of ureteral stents. In addition, some cases of percreta require additional skills such as the ability to reimplant ureters, repair major blood vessels, or resect bowel. Such cases require specialists such as gynecologic oncologists, vascular surgeons, urologists, or general surgeons.
Anesthesiologists experienced in both massive hemorrhage and obstetrics are other key players in the care of women with placenta accreta. The anesthesiologist is often the “quarterback” for the intraoperative medical care of women with massive hemorrhage. They assess vital signs, oxygenation, urine output, serum electrolytes, hematocrit, and coagulation status. They make decisions regarding the use of vasopressors and administration of blood products. The skills needed to perform these tasks optimally are best developed with repetition and experience. The unique physiologic changes in pregnancy require specialized knowledge and training in obstetric anesthesiology to optimize outcomes.
Ideally, preoperative consultation and evaluation should be performed. The patient should have 2 large-bore intravenous catheters placed, pneumatic compression stockings, equipment for rapid infusion of blood products and patient warming, and in most cases, access for hemodynamic monitoring (eg, arterial line and central venous line). Although clear data are lacking, general anesthesia is often preferred due to the potential for severe hemorrhage and prolonged surgery. However, in some cases neuraxial anesthesia or combined neuraxial and general anesthesia may be considered. The ability to rapidly convert to general anesthesia is important if neuraxial anesthesia is used.
One of the most important features of a center of excellence is a state-of-the-art, well-stocked blood bank that functions at full capacity 24 hours a day, 7 days a week. The blood bank should have a well-established massive transfusion protocol, as the median estimated blood loss in 3 well-characterized series of accreta cases was 2.5-3.0 L. There should be abundant fresh frozen plasma, cryoprecipitate, platelets, cell-saver technology, the availability of recombinant activated factor VII, and other alternative blood products. Transfusion medicine specialists are essential team players, who act as captain of the blood bank and can direct preparation of essential blood products, suggest alternatives if type-specific products are in short supply, and assist in monitoring trends in coagulation profiles, whether using standard labs or thromboelastography. In many cases of intraoperative emergency, the transfusion medicine specialist may need to take over the decision-making about blood product transfusion and electrolyte management. In such a situation, the anesthesia team may be too occupied with starting and managing large-bore central vascular access, vasopressor titration, and ventilation needs to monitor and deal with the rapidly changing potassium and calcium levels (sometimes life-threatening) that follow massive transfusion. In addition a variety of coagulation products can be required in huge amounts. The presence of an experienced transfusion medicine expert can distribute the workload and improve the quality of care. The necessity for a well-stocked blood bank cannot be overstated.
The capacity to perform therapeutic interventional radiologic procedures is also highly desirable. Some groups advise preoperative placement of pelvic artery balloon catheters with occlusion after delivery of the infant but prior to hysterectomy. The procedure is controversial since the potential for decreased bleeding may be offset by serious complications such as damage to large arteries including abscess formation, arterial thrombus, and hematomas that may require further intervention. Thus, it is not routinely advised. Nonetheless, postoperative bleeding may be diffuse due to consumptive coagulopathy and may not be amenable to simply identifying and “tying off” a bleeder. In such cases, radiographic embolization of large pelvic vessels may be lifesaving. Thus, qualified and experienced interventional radiologists should be part of the accreta team. The ability to embolize in the operating room, either using a hybrid operating room or a portable fluoroscopy C-arm and equipment, decreases the risk of decompensation during transportation to an interventional radiology suite.
Utilizing surgical technologists and circulating nurses familiar with accreta is extremely helpful, as with any specialized surgical procedure. Planned cesarean hysterectomy for accreta is often best performed in a “main” operating suite with equipment and access that may not be readily available on labor and delivery (eg, self-retaining retractors, cystoscopy, ureteral stents, point-of-care testing such as hematocrit and lactate). In such cases, labor and delivery nursing personnel should also circulate to address issues specific to obstetrics and neonatal resuscitation. If an institution prefers to perform these procedures on the labor and delivery unit, then arrangements should be made to have the appropriate equipment available.
Postoperatively, up to one-half of women with placenta accreta are admitted to an intensive care unit, which underscores the need for critical care services. Often a period of ventilator support is required postoperatively as women recover from extensive fluid resuscitation. This may be prolonged in cases of transfusion-related acute lung injury or pulmonary edema from fluid shifts. Rarely, patients require delay in abdominal closure due to packing used to tamponade residual venous bleeding, and may require prolonged sedation and ventilation. Some women require vasopressor support and invasive hemodynamic monitoring, which requires close surveillance, expert nursing care, or other specialized care that can only be provided in an intensive care setting. The intensivist caring for the accreta patient should have experience in postsurgical care, or the surgical team should have open access to the unit, as some women will have complications that require reoperation. Early detection of these complications is vital to avoid acute, irreversible decompensation.
The need for teamwork cannot be overstated. Effective communication among the surgeons, anesthesiologists, nurses, and blood bank are essential to good outcomes. This occurs only through practice, experience, as well as honest debriefing of each case with efforts made to constantly improve. Each case should undergo review with feedback regarding team interactions and performance. In addition, simulation exercises can help prepare team members for managing placenta accreta. Such exercises enhance teamwork and can reduce complications in emergent conditions on labor and delivery such as postpartum hemorrhage and shoulder dystocia. They can be low-fidelity and do not require sophisticated or expensive equipment. A key feature is videotaping the teams’ interactions with subsequent debrief and review, consequently enhancing subsequent teamwork.
Many centers also present each known or suspected accreta case at a multidisciplinary conference. This allows for optimal planning, preparation, and timing of delivery as well as consideration of any unique medical or social issues for each patient. Examples include but are not limited to prior pelvic or abdominal surgeries, known bladder invasion, positive antibody screens, objection to blood transfusion, comorbid medical conditions, and desire to preserve fertility. Such planning allows for optimization of the woman’s health. Consideration should be given to treatment with iron supplementation or erythropoiesis-stimulating agents to optimize the hematocrit, antenatal corticosteroids to enhance fetal pulmonary maturity, and use of a cell saver. The placental location can be identified antenatally or with the use of intraoperative ultrasound to allow mapping of the placental edge to avoid transecting the placenta at hysterotomy. A preoperative checklist is useful to insure that each patient receives optimal care and to reduce errors. Furthermore, consideration for an antenatal “suspected accreta” clinic can help in the streamlining and coordination of all these activities. One poorly studied and infrequently addressed aspect of placenta accreta and its attendant surgery is the psychosocial impact of the diagnosis, the loss of fertility, the persistent fear of death or bad outcome during the pregnancy, and the fear associated with the surgery. The addition of a social worker or psychiatrist to the team is an area for future research.
A final consideration for centers of excellence is the ability to adequately train future experts in the care of placenta accreta. The accreta epidemic is unlikely to abate any time soon. However, many recently graduated obstetrician gynecologists, maternal-fetal medicine fellows, and gynecologic oncology fellows have inadequate experience with placenta accreta to effectively manage these women. The high volume of cases cared for by such centers will ensure that future generations of women receive optimal care.
Risk factors for placenta accreta
Most placenta accretas occur in women with risk factors and can be antenatally diagnosed. By far, the strongest risk factor is placenta previa, especially when associated with multiple prior cesarean deliveries. In 1 large, multicenter prospective study, the risk of placenta accreta was 3% in women with placenta previa but no prior cesareans. However, women with placenta previa had an 11% risk for accreta with 1 prior cesarean, 40% risk with 2 prior cesareans, and >60% with ≥3 prior cesareans. It is noteworthy that multiple prior cesareans increase the risk for accreta, even in the absence of previa. The risk of accreta in women with no previa but ≥3 prior cesareans was about 1%. The risk is particularly high in the setting of cesarean scar ectopic pregnancies.
Another important risk factor is prior uterine surgery other than cesarean delivery, such as myomectomy, uterine curettage, and endometrial ablation. Asherman syndrome, fibroids, uterine abnormalities, and pelvic radiation also have been associated with accreta. However, it is difficult to calculate precise risks due to the rarity of these conditions. Additional minor epidemiologic risk factors include increasing maternal age and multiparity, perhaps due to an increased risk of previa and abnormal placentation, and in vitro fertilization.
It is critical to consider the diagnosis of placenta accreta in anyone with meaningful risk factors. This should include all women with: (1) any prior cesarean deliveries, (2) placenta previa or “low lying placenta,” (3) prior uterine surgery, and (4) Asherman syndrome, prior endometrial ablation, or pelvic irradiation. Patients with these risk factors should undergo a targeted sonogram to assess for possible placenta accreta in the mid second trimester ( Table 2 ). The sonogram should be accomplished by individuals with expertise and experience in the diagnosis of placenta accreta and the report should comment on the placental location in relation to the cesarean scar and whether or not sonographic features of accreta are present. Cases with continued suspicion for accreta after sonographic evaluation should be referred to an accreta center for delivery ( Table 3 ).
