Case Study
A 35-year-old gravida 3, para 2 woman (two previous cesarean deliveries) was admitted at 35 weeks’ gestation for steroid therapy administered for fetal lung maturation. Placenta accreta was suspected at the 32-week scan due to loss of regularity of the “retroplacental clear zone” and increased vascularity of the uterine serosa–bladder wall interface. The scan also revealed placenta previa. MRI was performed at 33 weeks’ gestation, confirming a complete placenta previa with the placenta thinning the myometrium of the uterine anterior wall, highly suspicious for placenta accreta. The patient was scheduled for cesarean delivery with likely hysterectomy at 36 weeks’ gestation. After the diagnosis, the patient underwent multidisciplinary counseling involving obstetricians, anesthesiologists, radiologists, and urologists. Prior to surgery, uterine artery angiography and catheterization were performed. The patient was transferred to the OR for cesarean delivery. During surgery, a protruding shiny-surface placenta was visualized in the lower uterine segment, cranial to the bladder, and 15 minutes following skin incision, a live-born infant was delivered. Both occlusion balloon catheters were inflated, and hysterectomy was performed with careful dissection of the planes to preserve the bladder. The estimated blood loss was 3,150 ml. The patient received 3 units of packed red blood cells, 3 units of fresh frozen plasma, and 1 unit of cryoprecipitate. She required overnight admission to the ICU and was discharged home 7 days following delivery.
Key Points
Placental attachment disorders (PADs) are life threatening diseases associated with significant morbidity and a maternal mortality rate of 7 percent.
The most common risk factors are placenta previa, previous cesarean delivery (particularly if repeated), and increased maternal age.
Obstetric ultrasound remains the primary tool for diagnosis, and MRI may be additionally helpful, but controversy still exists surrounding the most accurate technique because both modalities have high false-negative and false-positive rates for diagnosis.
The antenatal accuracy in the diagnosis of PAD should be improved to optimize peripartum maternal and neonatal outcomes.
Whenever PAD is suspected, careful planning and close communication are essential among anesthesiologists, obstetricians, interventional radiologists, hematologists, blood bank, and specialized surgical teams.
Discussion
Definitions
Placenta previa exists when the placenta is inserted wholly or partly into the lower segment of the uterus, partially or completely covering the internal cervical os. In cases of placenta previa, there should be a high index of suspicion for placenta accreta. Placental attachment disorders (PADs) encompass a spectrum of conditions characterized by abnormal adherence of the placenta to the uterine wall, with invasion of the placental villi through the decidua. Depending on the depth of invasion, it can be divided into three categories (accreta, increta, and percreta). PAD is commonly associated with placenta previa1, 2 (Figures 21.1 and 21.2).
Epidemiology, Risk Factors, Pathophysiology
Over the last 30 years, the incidence of PAD has increased 10-fold. In developed countries, reported rates range from 1 in 530 to 1 in 2,500 deliveries.3 The most common risk factors for PAD are placenta previa, previous cesarean delivery (particularly if repeated), and increasing maternal age. Less frequent risk factors include: multiparity, previous curettage, Asherman syndrome (acquired intrauterine adhesions/scarring or synechiae), and endometrial ablation. Two possible mechanisms of PAD formation have been proposed: abnormal decidualization or pathologic invasiveness of the trophoblast. The former has been considered in cases of alteration of the uterine wall, such as previous surgery, scars, and pelvic radiation,4, 5 whereas the latter may be explained by changes in the activity of growth and angiogenesis- and invasion-related factors within the trophoblast.6 Clinically, the most significant feature of placenta accreta is the abundant uteroplacental neovascularization, which can lead to life-threatening hemorrhage.7 Patients with PAD are often asymptomatic, but it can present with antepartum hemorrhage. If associated with placenta previa, it is a life-threatening disease and represents the second leading cause of peripartum hemorrhage, with a maternal mortality rate of 7 percent and significant morbidity due to blood loss, local organ damage, requirement for urgent hysterectomy (33–50 percent), and postoperative complications.8
Diagnosis
The Royal College of Obstetricians and Gynaecologists (RCOG) recommend that all pregnant women should be scanned at 20 weeks’ gestation to evaluate placental localization. If PAD is suspected, imaging should be performed at around 32 weeks’ gestation to clarify the diagnosis and allow planning for third-trimester management, including further imaging and delivery.2 Women with a “low-lying placenta” (diagnosed before 28 weeks) or a placenta previa (diagnosed after 28 weeks) that is overlying a uterine scar should be reevaluated in the third trimester, with attention paid to the potential presence of PAD.9
The main diagnostic tools are
Two-dimensional (2D) gray-scale and color Doppler ultrasound
Three-dimensional (3D) power Doppler ultrasound
MRI10
According to Shih et al.,11 in order to achieve the diagnosis of PAD, at least one of a number of criteria using 2D gray-scale or color Doppler ultrasound criteria should be present (Table 21.1). Three-dimensional power Doppler ultrasound can be performed as a complementary technique, as described in Table 21.1.
| 2D gray-scale or color Doppler criteria | 3D ultrasound |
|---|---|
| Complete loss or an irregular retroplacental sonolucent zone (Figure 21.3) | Intraplacental hypervascularity |
| Thinning or disruption of the hyperechoic uterine serosa–bladder interface | Inseparable cotyledonal, intervillous circulations |
| Focal exophytic masses invading the urinary bladder and abnormal placental lacunae | Tortuous vascularity with “chaotic branching” |
| Diffuse or focal lacunar flow pattern (Figure 21.4) | |
| Sonolucent vascular lakes with turbulent flow | |
| Hypervascularity of the uterine serosa–bladder interface with abnormal blood vessels linking the placenta to the bladder (Figure 21.5) | |
| Markedly dilated vessels over the peripheral subplacental region |
Figure 21.3 Loss and irregularity of retroplacental sonolucent zone
Figure 21.5 Hypervascularity of the uterine serosa–bladder interface with abnormal blood vessels linking the placenta to the bladder
The techniques listed in the table were found to achieve a sensitivity of 92–100 percent, a specificity of 68–85 percent, and a positive predictive value of 76–88 percent.2, 11 MRI is no better than ultrasound, although it may be superior at detecting the depth of trophoblast invasion.12 Dwyer et al.13 showed comparable sensitivity between ultrasound and MRI. The main MRI features of placenta accreta include uterine bulging, heterogeneous signal intensity within the placenta, and dark intraplacental bands on T2-weighted imaging.14 Many authors have recommended MRI for women in whom ultrasound findings are inconclusive.15 The “gold standard” for diagnosis remains pathology examination after hysterectomy characterized by the absence of decidua at the placental attachment site with the chorionic villi invading deeply into the myometrium. Intraoperative diagnosis of PAD can be made when the placenta is adherent to the uterine wall with difficulty at removal and excessive hemorrhage even with minimal placental separation.16
Planning for Delivery
If PAD is suspected, a detailed plan for follow-up, timing for delivery, multidisciplinary discussion, and patient consent is required. The discussion with the patient should include possible maternal complications, neonatal morbidity, and interventions such as interventional radiology, cell salvage during surgery, leaving the placenta in situ, and hysterectomy.2 The recommended gestational age for elective cesarean delivery is usually by 36–37 weeks of gestation, before labor is likely to occur, so as to avoid emergency delivery of a woman in labor who may already be compromised by hemorrhage. Administration of maternal steroids is recommended to mature the fetal lungs and prevent transient tachypnea of the newborn, which is more likely following elective cesarean delivery before 37 weeks. Women should be encouraged to take oral iron to boost their iron stores and optimize their hemoglobin level.
Careful discussion in the case of women who refuse blood products is paramount, including documentation of which products they might consider accepting. A signed and witnessed advance decision document listing the blood products and autologous procedures that are or are not acceptable to them should be filed and a copy retained by the patient during pregnancy. There is usually no objection to intraoperative cell salvage, apheresis, hemodialysis, cardiac bypass, or normovolemic hemodilution, provided that the equipment is primed with nonblood fluids. Recombinant products, such as erythropoiesis-stimulating agents (e.g., RHuEpo) and granulocyte colony-stimulating factors (e.g., G-CSF or GM-CSF) are acceptable, as are pharmacologic agents such as IV iron or tranexamic acid. Guidelines for the use of recombinant factor VII (rFVIIa) in massive obstetric hemorrhage have been developed, although current evidence to date for use of rFVIIa in postpartum hemorrhage is limited to case reports and case series with one nonrandomized study.17
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