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The steady rise of cesarean delivery has led to a steady increase in this potential obstetric emergency.
Dr Esakoff is Assistant Clinical Professor of Obstetrics and Gynecology, Division of Maternal Fetal Medicine, Cedars Sinai Medical Center, Los Angeles, California.
Morbidly adherent placenta (MAP) includes the continuum of placenta accreta, increta, and percreta. The incidence of placenta accreta has steadily increased in recent decades, from 1 in 2510 pregnancies in the early 1980s to 1 in 533 pregnancies in the period 1982–2002.1-3 Placenta accreta carries a mortality rate of up to 10% and accounts for the majority of cesarean hysterectomies performed.4 Risk factors include prior uterine surgery, placenta previa, advanced maternal age, and parity of 3 or more.3
Interestingly, a recent large maternal-fetal medicine units (MFMU) study found that prior myomectomy does not appear to be associated with higher risk of placenta accreta. The climbing cesarean delivery rate, however, is thought to be directly linked to the increasing incidence of accreta.5 In the 1970s, the overall cesarean rate was 5.5% but by 2012, it had increased to 32.8% of all deliveries.6 The striking link between history of cesarean and placenta accreta was illustrated in a study comparing the number of prior cesareans and the risk of placenta accreta in the current pregnancy7 (Table 1). Even in the absence of a placenta previa in the current pregnancy, the risk of accreta was almost 5% in the setting of 5 prior cesareans. If the patient had a previa in the current pregnancy, the risk rose to 40% with just 2 prior cesareans7 (Table 1).
Placenta accreta has been associated with an increased risk of cystotomy, ureteral injury, pulmonary embolism, need for ventilator use, and an increased risk of intensive care unit (ICU) admission7 as well as greater blood loss at delivery, with a mean of 3000–5000 mL.4 A theoretical study reported that if the cesarean rate were to increase from 29% to 34% there would be an additional 14 to 32 maternal deaths, 5000 to 24,000 surgical complications, 4000 to 6000 post-op infections, 200 to 300 venous thromboses, 33,000 neonatal intensive care unit admissions, and 2200 more readmissions. There would also be 930,000 additional hospital days and over $1 billion in additional health care spending.8
MAP refers to abnormal adherence of the chorionic villi to the myometrium. The type of abnormal placentation present depends on the degree of trophoblastic invasion. If only the Nitabuch’s layer is absent, a placenta accreta is present. Invasion extending into the myometrium is an increta, and if there is invasion beyond the uterine serosa, a placenta percreta is present.9 Diagnosis is typically made by ultrasound. Findings that raise suspicion for the presence of placenta accreta include loss of the hypoechoic boundary between the placenta and bladder,10 ultrasonographic presence of lacunae,11,12 and increased vascularity on color Doppler. Myometrial thickness < 1 mm and loss of visualization of the myometrium have also been used.13-15 The presence of lacunae has the highest sensitivity of almost 100%11,12 (Figure 1). In general, ultrasound is an excellent screening test for accreta, with a sensitivity of 77%–93%16-19 and a specificity of 71%–91%.16-19
The utility of magnetic resonance imaging (MRI) for diagnosis is controversial although it may be useful when there is a concern for percreta, a posterior accreta is suspected, the focus of suspected accreta is at an unusual site, or the ultrasound is negative for accreta but clinically the concern is high. A recent systematic review of MRI features that can be useful in the diagnosis of placental adhesion disorder found that T2 dark intraplacental bands, heterogeneity of the placenta, abnormal uterine bulging, and disruption of the uteroplacental zone were the criteria most commonly used. MRI sensitivity and specificity varied between 75%–100% and 65%–100%, respectively. Antenatal diagnosis by either ultrasound or MRI can be valuable.20 A recent study reported a trend toward decreased estimated blood loss and need for blood products when placenta accreta was suspected prenatally and appropriate delivery preparations were made.21
Data are limited on optimal antepartum management of MAP. In general, antenatal testing with nonstress tests is not felt to be indicated because placenta accreta is not reported to be associated with an increased risk of placental insufficiency. The optimal interval for follow-up ultrasounds is also not known. Delivery should be planned at an institution with appropriate surgical facilities and transfusion capability. Predelivery hemoglobin levels should be maximized with iron supplementation. A recent retrospective cohort study found that a multidisciplinary approach to the delivery resulted in less blood loss (2.1 L vs 3.0 L, P = 0.025) and less likelihood of emergent delivery.22
Timing of delivery remains controversial and depends on specific clinical circumstances and the extent of placental invasion. A decision analysis from 2010 compared 9 different strategies regarding the timing of delivery as they relate to maternal ICU admission, perinatal mortality, infant mortality, respiratory distress syndrome, mental retardation, and cerebral palsy.23 Delivery at 34 weeks was the preferred strategy with the highest quality-of-life years. Strategies for awaiting confirmation of fetal lung maturity did not have better outcomes compared to outright delivery.23 A more recent study reported that scheduled delivery at 34 weeks would avoid 27% of emergent deliveries.24
Proper preparation for surgery is essential. Placing the patient in dorsal lithotomy position and using stirrups allow direct assessment of vaginal bleeding and extra access if the procedure becomes more extensive. Padding and positioning should be used to avoid nerve injury. The choice of excision should be made based on a patient’s body habitus.
The gold standard is planned preterm cesarean hysterectomy in which the placenta is left in situ.25 Attempts at placenta removal are associated with a high risk of hemorrhage,24 so attempts to remove the placenta manually should be avoided. Because it is not clear if there is a benefit to total versus subtotal hysterectomy, this decision is provider-dependent.
Recently some data have emerged on conservative management of placenta accreta. In these instances either a part of the placenta or the entire placenta is left in situ and the patient may be managed expectantly, have uterine artery embolization (UAE), or have adjuvant medical treatment with such medications as methotrexate, mifepristone, and misoprostol. A review of 60 cases in the literature found that the rate of treatment failure (inability to preserve the uterus) was 15% for conservative therapy alone, 23% for conservative therapy and methotrexate, and 25% for conservative therapy and UAD.26 Overall, however, treatment was successful (ie, the uterus was preserved) in 80% of cases but the risk of recurrence of accreta in a subsequent pregnancy was 60%. Complications included fever, endometritis, and disseminated intravascular coagulation (DIC).26
Similarly, in a retrospective study of 50 cases of abnormal placentation, half of the patients underwent hysterectomy while the other half were managed conservatively. Of those managed conservatively, 92% required additional therapy (medical, surgical, or UAD) and 19% failed conservative treatment. Complications included fever and DIC.27
The largest study to date evaluating outcomes in the setting of conservative management was performed in France between 1993 and 2007 and included 40 university hospitals. A total of 167 women underwent conservative treatment and the success rate was 78.4%.28 Half of the patients in whom conservative therapy failed underwent primary hysterectomy, while the other half had delayed hysterectomy. Severe maternal morbidity occurred in 6% and included sepsis, peritonitis, vesicouterine fistula, and uterine necrosis. Spontaneous placental resorption occurred in 75%, but the remaining patients needed hysteroscopic resection or curettage. The median resorption time from delivery was 13.5 weeks with a range of 4 to 60 weeks.28
The position of the American College of Obstetricians and Gynecologists (ACOG) is that conservative management is appropriate only when blood loss is minimal, the patient has a strong desire for fertility preservation, she understands that the outcome is unpredictable and there is no guarantee of a subsequent pregnancy, adequate technical support is available, and rigorous surveillance is provided.25
Balloon-assisted occlusion of the internal iliac arteries has been used in an attempt to decrease the morbidity associated with placenta accreta. Balloon-tipped catheters are placed in a retrograde fashion through the femoral arteries immediately before surgery and are inflated after delivery and during the dissection. Another option is preoperative placement of femoral access by interventional radiology with selective embolization of the uterine vessels at the time of delivery.
The literature is inconsistent as to the benefits of these procedures. Though there have been reports of significantly less blood loss and fewer blood transfusions as well as shorter duration of surgery, other studies have not demonstrated a difference.29-33 In addition, some studies have reported an increased risk of vessel thrombosis/dissection, insertion site hematoma, abscess, necrosis, and pseudoaneurysms.29,33
UAE has also been used postoperatively to manage persistent hemorrhage associated with placenta accreta. The success rate (ability to preserve the uterus) appears to be 62%–77% with a failure rate of 23% and a complication rate of 11%.34-39 Complications include fever, allergic reaction, pelvic infection, and ischemic phenomena.34-39 In women who underwent UAE for abnormal placentation, 83% had return of menses and 15% were able to become pregnant. The risk of recurrence of abnormal placentation was 18%.34
ACOG’s position is that “current evidence is insufficient to make a firm recommendation on the use of balloon catheter occlusion or embolization to reduce blood loss and improve surgical outcome, but individual situations may warrant their use.”25
Ureteral stent placement has recently been proposed as an adjunct procedure to help decrease the risk of ureteral injury. The potential benefit is that stents may help identify a ureteral injury during the procedure and may help decrease the amount of bleeding by reducing the amount of time needed to identify the ureter.40,41 The potential risks include the increased risk of injury due to decreased pliability, the 1% risk of iatrogenic injury, and the possibility that the stents may situate the ureter in an ectopic location, thereby increasing the risk of injury.42-45 Use of stents is controversial and available data on it are limited.46
Both general and regional anesthesia are considered to be safe for delivery of a patient with abnormal placentation. Each patient’s care should be individualized.25,47-49 Massive transfusion protocol should be initiated early if a patient has significant bleeding. That involves early administration of fresh frozen plasma (FFP), platelets, and packed red blood cells (PRBCs) in a 1:1:1 ratio. The goal is to rapidly correct coagulopathy and to decrease the need for transfusion postoperatively. Preoperative autologous blood donation can be considered in patients with rare blood types or alloimmunization to rare antibodies.
Until recently, the use of a cell saver system in obstetrics was limited by concerns regarding amniotic fluid embolism (AFE) and Rhesus isoimmunization. Current filtering technology eliminates theoretical concern for AFE but the risk of alloimmunization from fetal RBCs remains.50-53 A recent review of the literature on cell saver use in obstetrics revealed no significant problems,54 but it is not available emergently and is expensive.
Debate continues regarding the best overall management strategy for MAP. A recent study of 76 patients found that a scheduled cesarean delivery with no attempt at placental removal and use of ureteral stents decreased mean blood loss and early morbidity.24 Nevertheless, practice patterns of physicians across the United States are variable. A survey of US maternal-fetal medicine specialists registered with the Society for Maternal-Fetal Medicine reported that most providers believe that hysterectomy is the only management strategy for abnormal placentation but 32% had attempted conservative management at some point. Approximately 35% of providers use ureteral stents and 36% use internal femoral artery balloons, with significant variation by region.55
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