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ORIGINAL ARTICLE
Year : 2018  |  Volume : 31  |  Issue : 3  |  Page : 1023-1029

Role of ultrasound, Doppler, and MRI in the diagnosis of placenta accreta


Department of Radiodiagnosis, Faculty of Medicine, Menoufia University, Menoufia, Egypt

Date of Submission22-Jan-2017
Date of Acceptance23-Mar-2017
Date of Web Publication31-Dec-2018

Correspondence Address:
Heba M Abdel Rahman
Faculty of Medicine, Menoufia University, Menoufia
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/mmj.mmj_80_17

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  Abstract 


Objectives
The objectives of this study were to compare the accuracy of ultrasonography and MRI for prenatal diagnosis of placenta accreta (PA) and to compare the sensitivity and specificity of individual ultrasonographic and MRI markers in predicting placental invasion in cases of PA.
Background
PA is a significant cause of maternal morbidity and mortality, and at present it is the most common reason for emergent postpartum hysterectomy. Placenta previa and previous cesarean section are the two most important known risk factors for PA. Accurate prenatal identification of affected pregnancies allows optimal obstetric management. Ultrasonography still remains the diagnostic standard. However, in recent years, there has been increased interest in MRI in evaluating PA.
Patients and methods
A combined prospective and retrospective study was carried out on 20 pregnant women with persistent placenta previa (after 28 weeks gestation). All patients were subjected to history taking, complete medical examination, and ultrasound, Doppler, and MRI.
Results
The sensitivity and specificity of ultrasonography were 63.6 and 91.6%, whereas the sensitivity and specificity of MRI were 72.70 and 100%, respectively, in their ability to diagnose PA.
Conclusion
MRI hand-in-hand with ultrasound is important for the accurate diagnosis of placenta previa and the serious coexisting PA. Use of both modalities may provide more diagnostic information.

Keywords: magnetic resonance imaging, placenta accreta, placenta previa, ultrasonography


How to cite this article:
El Wakeel A, Azab S, Abdel Rahman HM. Role of ultrasound, Doppler, and MRI in the diagnosis of placenta accreta. Menoufia Med J 2018;31:1023-9

How to cite this URL:
El Wakeel A, Azab S, Abdel Rahman HM. Role of ultrasound, Doppler, and MRI in the diagnosis of placenta accreta. Menoufia Med J [serial online] 2018 [cited 2019 Mar 20];31:1023-9. Available from: http://www.mmj.eg.net/text.asp?2018/31/3/1023/248765




  Aim Top


This study was conducted to compare the accuracy of ultrasonography (US) and MRI in the prenatal diagnosis of placenta accreta and to compare the sensitivity and specificity of individual ultrasonographic and MRI markers in predicting placental invasion in cases of placenta accreta.


  Introduction Top


Although statistically a rare complication, placenta accreta has now become an important etiology of maternal morbidity and mortality[1]. Owing to the increasing rate of Cesarean delivery, there has been a 10-fold rise in the incidence of placenta accreta since the 1970s[2].

Clinically, the most significant feature of placenta accreta is the abundant uteroplacental neovascularization, which can lead to life-threatening hemorrhage[3]. However, its antenatal diagnosis is usually based on characteristic findings on gray-scale ultrasound imaging, such as the loss of subendometrial echolucent zone or the presence of abnormal placental lacunae[4].

Several reports have suggested that neither color Doppler nor power Doppler can assess uteroplacental vascularization or add any additional information to gray-scale ultrasound imaging in the diagnosis of placenta accreta[5]. However, much of the literature on this subject either describes single cases or lacks adequate controls (i.e., placenta previa without accreta), making it rather difficult to validate existing criteria[6].

Despite the modern advances in imaging techniques, no single diagnostic technique affords complete assurance for the presence or absence of placental accreta[7].


  Patients and Methods Top


Study population and selection of patients

The present study included 20 cases of persistent placenta previa (after 28 weeks gestation) at high risk with coexisting placental invasion (accreta). The study protocol was approved by the Local Ethics Committee of Menoufia University.

Inclusion criteria

  • Pregnant women with persistent placenta previa (after 28 weeks of gestation), with implantation on the lower uterine segment
  • Previous uterine surgery (e.g., cesarean section, myomectomy, or fractional curettage).


Exclusion criteria

  • Presence of medical disorders (diabetes, hypertension, epilepsy, etc.)
  • Presence of metallic prosthesis (metallic prosthetic valves, pacemakers, cochlear implants, or plates and screws).


Each patient in this study was subjected to the following:

  • Full history taking including their past histories of uterine surgery such as a previous cesarean delivery
  • Informed consent was obtained before scanning
  • Complete imaging using all diagnostic techniques: gray scale, color Doppler by the same operator, and MRI.


Ultrasound examination was carried out using Toshiba Femio 5 (Toshiba Medical Solutions Inc., Tochigi, Japan) equipped with a 4–8-MHz transabdominal transducer.

MRI examination was carried out using Siemens Aera 1.5-T scanner (Siemens Healthineers, Tashkent, Uzbekistan, U.S.). Images were obtained in the supine and left decubitus positions, in the axial, sagittal, and coronal planes, and the balanced, fast-field echo and the single-shot, turboSpin echo sequences were used.

For each patient, the whole placenta was scanned in a systematic manner using both gray-scale ultrasound and color flow mapping followed by MRI.

The placenta was imaged with sufficient bladder volume to clearly visualize the serosa–bladder interface, the angle of insonation was kept as low as possible, and the resistance index of flow within the abnormal lacunae and any newly formed vessels over the serosa–bladder border was measured in at least three different locations to obviate selection bias, with the lowest value being used for analysis.

On gray-scale ultrasound imaging, we considered the presence of at least one of the following characteristics to indicate placenta accreta (including its variants, placenta increta and placenta percreta):

  • Complete loss of the retroplacental sonolucent zone
  • Irregular retroplacental sonolucent zone
  • Thinning or disruption of the hyperechoic uterine serosa–bladder interface
  • Presence of focal exophytic masses invading the urinary bladder
  • Presence of abnormal placental lacunae[8]. They often appear to be parallel, linear, vascular channels extending from the placental parenchyma into the myometrium. These entities differ from vascular lakes in that they appear more indistinct and show turbulent flow, whereas lakes appear more rounded with laminar flow
  • Decreased myometrial thickness (<1 mm).


Likewise, the diagnosis of placenta accreta was regarded as positive when any one of these color Doppler criteria was present:

  • Diffuse or focal lacunar flow pattern
  • Sonolucent vascular lakes with turbulent flow typified by high-velocity (peak systolic velocity>15 cm/s) and low-resistance waveform
  • Hypervascularity of the uterine–bladder interface with abnormal blood vessels linking the placenta to the bladder (areas of increased vascularity and continuum of lacunar flow from the placenta through the myometrial layer without intervening clear space)
  • Markedly dilated vessels over the peripheral subplacental region[9].


In addition, the diagnosis of placenta accreta was regarded as positive when any one of these MRI criteria was present:

  • Uterine bulging
  • Heterogeneous signal intensity within the placenta
  • Focal interruptions in the myometrial wall
  • Dark intraplacental bands on T2-weighted images.


To analyze the angioarchitecture of the lower uterine segment and placenta, we carried out a two-dimensional power Doppler examination targeted to this region, and the views were successively evaluated: the lateral view was used to observe the intraplacental vasculature and serosa–bladder complex along the sagittal axis of the maternal pelvis, and the basal view illustrated the serosa–bladder interface in a 90° rotation of the lateral view (observed from the direction of the bladder).

As the abundant neovascularization of the uteroplacental region is a notable feature of placenta accreta, we further analyzed the patterns of placental vasculature in an attempt to differentiate between placenta previa totalis and placenta accreta.

All pregnant women enrolled in this study delivered by cesarean section at our hospital with full availability of information on delivery.

Definitive diagnosis of placenta accreta was made at delivery when the myometrium was seen to be invaded by the placenta, and the pathological examination of the removed uterus showed the villi attached to the myometrium without intervening decidua (accreta), invading into the myometrium (increta), or reaching the serosa (percreta).

Statistical analysis

Precoded data were entered into the statistical package for the social sciences software program, version 21 to be statistically analyzed (SPSS Inc., Chicago, Illinois, USA).

Data were summarized using means and SDs for quantitative variables and using frequencies and percentages for qualitative ones.

Comparison between groups was performed using Kruskal–Wallis and Mann–Whitney U tests for quantitative variables and the χ2-test for qualitative ones.

P values less than 0.05 were considered statistically significant.

Graphs were used to illustrate some information.


  Results Top


The present study included 20 cases of placenta previa at high risk with coexisting placental invasion (accreta).

A total of 20 gravid women with placenta previa were statistically evaluated in the present study, with a mean age of 30.96 years. Their gestational age ranged from 28 to 37 weeks.

Eleven of these 20 patients had a diagnosis of placenta accreta clinically at delivery, by pathological examination, or both. Their ages ranged from 20 to 37 years with a mean age of 29.64 years, and all of them had undergone previous uterine surgeries. Patient details are provided in [Table 1].
Table 1: Characteristics of patients with placenta accreta

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Among the 11 cases proved to have placenta accreta, three had placenta percreta, six had placenta accreta, and two had placenta increta.

Nine women had only placenta previa with no accreta. History of previous uterine surgeries was elicited in eight out of nine cases.

Ultrasound and MRI examinations were performed for all 20 patients between 28 and 37 weeks of gestation.

Out of the 20 cases, US suggested diagnosis of placenta previa/accreta in eight patients and placenta previa without accreta in 12 cases.

According to the operative findings and/or pathological studies, seven out of the eight (87.5%) patients were proved to be true positive and one (12.5%) was found out to be false positive.

Among the 12 patients, eight (66.7%) were found out to be true negative and four (33.3%) were found to be false negative.

Findings that were suspicious of placenta accreta were observed in seven out of 11 (45.5%) patients. The results of these scans are shown in [Table 2].
Table 2: Sonographic findings in true-positive cases of placenta accreta

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Multiple findings were more common than a single isolated finding. In our study, obliteration of the retroplacental clear space was found in seven out of 11 (63.6%) cases, the interruption of the posterior bladder wall–uterine interface in six out of 11 (54.5%) cases, decreased myometrial thickness in six out of 11 (54.5%) cases, presence of placental vascular spaces in two out of 11 (18.2%) cases, and presence of hypervascularity of the interface between the uterine serosa and the bladder wall on color Doppler in five out of 11 (45.4%) cases.

All our patients underwent MRI at the same gestational age when they underwent US, for inconclusive or to confirm positive US findings. The MRI studies were performed at gestational ages of 28–37 weeks.

Of all 20 patients with placenta previa, MRI suggested diagnosis of placenta previa/accreta in eight out of 20 patients and placenta previa with no accreta in 12 out of 20 patients.

According to the operative findings and/or pathology, MRI was found to provide true-positive results in eight out eight (100%) patients proved to be accreta cases.

Out of the 12 patients found to have no accreta, MRI provided true-negative results in nine (75.0%) patients and false-negative results in three (25.0%) patients.

In our study, the MRI features of patients showed that they had accreta: heterogeneous placental signal intensity was found in seven out of 11 (63.64%), dark intraplacental bands in five out of 11 (45.5%), focal interruption in the myometrial wall in eight out 11 (72.73%), uterine bulging in three out of 11 (27.3%) cases, and direct visualization of invasion of pelvic structures in one (9%) case.

In our study, focal interruption in the myometrial wall was found to have the highest sensitivity (73.7%) followed by heterogeneous signal intensity within the placenta (63.6%) and then dark intraplacental bands (45.5%) [Table 3],[Table 4],[Table 5],[Table 6] and [Figure 1],[Figure 2],[Figure 3],[Figure 4].
Table 3: Sensitivity, specificity, positive predictive value, and negative predictive value of ultrasonography diagnostic criteria for placenta accreta

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Table 4: MRI findings in true-positive cases of placenta accreta

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Table 5: Sensitivity, specificity, positive predictive value, and negative predictive value of MRI diagnostic criteria for placenta accreta

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Table 6: Sensitivity, specificity, positive predictive value, and negative predictive value of ultrasound and MRI in this study

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Figure 1: Case 1: (a-c) transabdominal ultrasonography gray-scale and (d) color Doppler showing a thinned-out myometrium with loss of retroplacental clear space, suggesting placenta accreta.

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Figure 2: Case 1: placenta previa complete centralis. (a and b) MRI sagittal, coronal T2 and (c) sagittal T1-weighted fast-spin-echo showing uterine bulging of the lower uterine segment altering the normal pear shape of the gravid uterus and thickened inhomogeneous placenta infiltrating the inner layer of the myometrium at the lower uterine segment (arrow). Note the dark intraplacental band. Intact interface between the uterine serosa and the urinary bladder (site of previous cesarean section can be seen with fat anteriorly, arrowhead). A, anterior; P, Posterior.

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Figure 3: Case 2: placenta previa complete centralis with inconclusive ultrasonographic (US) findings. (a and b) Color Doppler US suspecting interruption in the retroplacental clear space.

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Figure 4: Case 2: (a-d) MRI sagittal and coronal T2-weighted fast-spin-echo and (e) coronal T1-weighted images: placenta previa complete centralis, thickened with placental infiltration, and interruption of the anterior and posterior parts of the lower uterine segment (arrow) with infiltration of the cervix (arrowhead). Note placental lacunae.

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  Discussion Top


The present study included 20 cases of placenta previa at high risk with coexisting placental invasion (accreta).

The present study was a prospective study to determine the need for MRI in the radiological diagnosis of candidate cases for placenta accreta. Sensitivity and specificity of US were 63.6 and 91.6%, whereas for MRI sensitivity and specificity were 72.70 and 100%, respectively, in their ability to diagnosis placenta accreta. This is in disagreement with a study performed in 2008, which stated that US had a sensitivity of 93% and specificity of 71% compared with MRI, which had a sensitivity of 80% and specificity of 65%[10].

Another comparable study confirmed that pelvic US using color Doppler is highly reliable to diagnose or exclude the presence of placental adhesive disorders (PAD), and found MRI to be an excellent tool for the staging and topographic evaluation of PAD. They stated that MRI and Doppler US show no statistical difference in identifying patients with PAD, whereas MRI was statistically better than Doppler US in characterizing the topography of invasion. MRI showed accuracy of 100% in assessing the depth of placental infiltration versus 75% by US[11].

A study by Dwyer et al.[10] showed an ascertainment bias as it was a retrospective study and criteria for MRI referral were not uniform.

Another study stated that the sensitivity and specificity of US were 86.6 and 80%, whereas MRI showed sensitivity and specificity of 93.3 and 85%, respectively, in their ability to diagnosis placenta accreta.

A recent study by McLean et al.[12] including a large cohort of gravid patients at risk for placenta accreta failed to demonstrate the incremental use of MRI for placenta accreta changes delivery mode in a stratified analysis. Such a study had performed MRI in a small proportion of the cohort that was only 28.7% (n = 40/139), also being a retrospective study handles a percentage of US bias regarding analytical data[12].

Warshak et al.[13] compared US and postcontrast MRI performance in the diagnosis and evaluation of placenta accreta. They reported on 39 cases of confirmed placenta accreta with an unpaired study design. Ultrasound had a sensitivity of 77% and specificity of 96%, and MRI with gadolinium enhancement had a sensitivity of 88% and specificity of 100%. The high statistical values in the aforementioned study may be because they had performed routine transvaginal ultrasound in addition to the transabdominal approach in evaluating their studied cases as well as gadolinium enhancement in their MRI examination, as according to them it had more clearly delineated the outer placental surface relative to the myometrium[14].

Masselli et al.[11] stated that the presence of lacunae in the placenta was the most predictive sonographic sign of PAD with sensitivity of 79% and a positive predictive value (PPV) of 92% compared with our study with a sensitivity of 18.8% and PPV of 100%.

The difference in the specificity of sonography between studies could be due to the fact that transvaginal sonography was used in their studies but was not routinely used in our study.

Lax et al.[14] described three new secondary signs of abnormal placentation on MRI: irregular thick intraplacental T2 dark bands, marked placental heterogeneity, and bulging of the lower uterine segment. Homogeneous placentas were overwhelmingly benign, and markedly heterogeneous placentas with T2 dark bands were associated with invasive placentation[14], postulating that the abnormal T2 dark bands were the result of fibrin deposition.

Our study agrees with the findings of Lax et al.[14]. We also found that the focal interruption in the myometrium was seen in 72.7%, abnormal heterogeneous signal intensity of the placenta was seen is 63.6%, dark intraplacental bands on T2 sequences was seen in 45.5% of the surgically/pathologically proved cases of placenta accreta, and were absent in most normal placentas.

Recently, Yang et al.[15] in a small retrospective study proposed the analysis of the intensity of the inner, middle, and outer layers of this interface and suggested that the obliteration of the inner layer without other abnormalities can depict the condition of PAD.

In our series, the most effective ultrasound criteria for detecting placenta accreta were abnormal clear space and loss of uterine serosa–bladder wall interface with negative predictive value (NPV) of 75.0 and 70.59%, respectively. Comstock's review[16] according to Finberg and Williams[17] underlined that loss of the echolucent area between the placenta and the uterus accounts for the majority of false positives, and this criterion should not be used by itself to make a diagnosis.

Moreover, our data suggest that the lack of loss/irregularity of clear space may help exclude the diagnosis of placenta accreta. If the echolucent area between the placenta and the uterus is preserved, especially in cases of low anterior placenta, placenta accreta is unlikely to occur. We therefore confirm the findings of Comstock[16] and Finberg and Williams[17] that the clear space should not be used as a single diagnostic criterion, but should be combined with other criteria with greater PPV.

We looked for intraplacental lacunae using gray-scale and color Doppler imaging. Our investigative hypothesis was to determine a relationship between intralacunar turbulent flow and grade of placenta accreta[8],[18]. All cases with placenta percreta had more than six lacunae with turbulent flow inside. In our series, placenta lacunae had a relatively high PPV and low NPV of 100 and 57.14%, respectively, whereas a strong relationship between multiple placental lacunae with irregular shape and placenta accreta has been suspected by other authors[15],[17]. We found that bladder line thinning and/or interruption had high specificity and PPV, as stressed by Finberg and Williams[17].

The strengths of our study are as follows:

  • It evaluated the individual ability of MRI and ultrasound to predict placenta accreta in the same group of cases
  • Sensitivity and specificity of MRI were estimated without the use of gadolinium, which is the approach most suitable for gravid patients, as the European Medicines Agency warns against the use of gadolinium before the first year of life.


In this study, we relied upon spin echo sequences in assessing placental invasion to the myometrium or beyond as follows:

  • T2-weighted images helped in distinguishing the intermediate signal intensity placental bulk from the inner and outer myometrial dark layers as well as from the myometrium itself, which is of more intermediate signal intensity
  • T1-weighted images showed distended tortuous placental/myometrial vessels as clustered bright signal intensities (probably due to blood stagnation, especially in the pelvic and lower limb vessels accompanying pregnancy). The interface between the urinary bladder and the myometrium was also more clarified at that sequence. T2-weighted images may display overestimation of percreta. In such cases, we had to check for disruption of the fat plane overlying the uterine serosa in T1-weighted sequence.



  Conclusion Top


US remains the diagnostic standard, and routine US examination at 18–20 weeks of gestation allows an ideal opportunity to screen for the disorder. This modality has enjoyed great popularity because it is widely available, patient friendly, and relatively inexpensive.

MRI has higher specificity, sensitivity, PPV, NPV, and accuracy over US. However, MRI is an expensive investigation, and therefore it can be reserved for patients with inconclusive ultrasound criteria

Owing to the high costs of MRI, it could be reserved for cases with inconclusive US findings and cases with posterior placenta previa to improve diagnostic accuracy.

Our study limitations include patients with metallic prosthesis (metallic prosthetic valves, pacemakers, cochlear implants, plates, and screws) who are not candidates for MRI.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Dildy GAIII. Postpartum hemorrhage: new management options. Clin Obstet Gynecol 2002; 45:330–344.  Back to cited text no. 1
    
2.
Wu S, Kocherginsky M, Hibbard JU. Abnormal placentation: twenty-year analysis. Am J Obstet Gynecol 2005; 192:1458–1461.  Back to cited text no. 2
    
3.
Tseng JJ, Chou MM, Hsieh YT, Wen MC, Ho ES, Hsu SL.. Differential expression of vascular endothelial growth factor, placenta growth factor and their receptors in placentae from pregnancies complicated by placenta accreta. Placenta 2006; 27:70–78.  Back to cited text no. 3
    
4.
Comstock CH, Love Jr JJ, Bronsteen RA, Lee W, Vettraino IM, Huang RR, et al. Sonographic detection of placenta accreta in the second and third trimesters of pregnancy. Am J Obstet Gynecol 2004; 190:1135–1140.  Back to cited text no. 4
    
5.
Thia EW, Lee SL, Tan HK, et al. Ultrasonographical features of morbidly-adherent placentas. Singapore Med J 2007; 48:799–803.  Back to cited text no. 5
    
6.
Okada M, Mitsui T, Morita T, Nomura M, Ohta T, Itakura A. Acase of placenta accreta complicated by severe IUGR and maternal coagulopathy. Acta Obstet Gynecol Scand 2007; 86:760–762.  Back to cited text no. 6
    
7.
American College of Obstetricians and Gynecologists. ACOG Practice Bulletin: Clinical Management Guidelines for Obstetrician–Gynecologists Number 76, postpartum hemorrhage. Obstet Gynecol 2006; 108:1039–10472.  Back to cited text no. 7
    
8.
Lerner JP, Deane S, Timor-Tritsch IE. Characterization of placenta accreta using transvaginal sonography and color Doppler imaging. Ultrasound Obstet Gynecol 1995; 5:198–201.  Back to cited text no. 8
    
9.
Comstock CH, Love Jr JJ, Bronsteen RA, Lee W, Vettraino IM, Huang RR, et al. Sonographic detection of placenta accreta in the second and third trimesters of pregnancy. Am J Obstet Gynecol 2005; 190:1135–1140.  Back to cited text no. 9
    
10.
Dwyer BK, Belogolovkin V, Tran L, Rao A, Carroll I, Barth R, et al. Prenatal diagnosis of placenta accreta: sonography or magnetic resonance imaging? Ultrasound Med. 2008; 27:1275–1281.  Back to cited text no. 10
    
11.
Masselli G, Brunelli R, Casciani E, Polettini E, Piccioni MG, Anceschi M, et al. Magnetic resonance imaging in the evaluation of placental adhesive disorders: correlation with color Doppler ultrasound. Eur Radiol 2008; 18:1292–1299.  Back to cited text no. 11
    
12.
McLean LA, Heilbrun ME, Eller AG, Kennedy AM, Woodward PJ. Assessing the role of magnetic resonance imaging in the management of gravid patients at risk for placenta accreta. Acad Radiol. 2011; 18:1175–1180.  Back to cited text no. 12
    
13.
Warshak CR, Eskander R, Hull AD, Scioscia AL, Mattrey RF, Benirschke K, et al. Accuracy of ultrasonography and magnetic resonance imaging in the diagnosis of placenta accreta. Obstet Gynecol 2006; 108:573–581.  Back to cited text no. 13
    
14.
Lax A, Prince MR, Mennitt KW, Schwebach JR, Budorick NE. The value of specific MRI features in the evaluation of suspected placental invasion. Magn Reson Imaging 2007; 25:87–93.  Back to cited text no. 14
    
15.
Yang JI, Lim YK, Kim HS, Chang KH, Lee JP, Ryu HS. Sonographic findings of placental lacunae and the prediction of adherent placenta in women with placenta previa totalis and prior cesarean section. Ultrasound Obstet Gynecol 2006; 28:178–182.  Back to cited text no. 15
    
16.
Comstock CH. The antenatal diagnosis of placenta accreta. Curr Opin Obstet Gynecol 2011; 23:117–122.  Back to cited text no. 16
    
17.
Finberg HJ, Williams JW. Placenta accreta: prospective sonographic diagnosis in patients with placenta previa and prior cesarean section. J Ultrasound Med 1992; 11:333–343.  Back to cited text no. 17
    
18.
Guy GP, Peisner DB, Timor-Tritsch IE. Ultrasonographic evaluation of uteroplacental blood flow patterns of abnormally located and adherent placentas. Am J Obstet Gynecol 1990; 163:723–727.  Back to cited text no. 18
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]



 

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