Does MRI Help or Hurt When Making a Diagnosis of Placenta Accreta?
BACKGROUND AND PURPOSE:
Incidence of Placenta Accreta Spectrum Disorder is rising
Estimated at 1/500-1/300 pregnancies
Ultrasound is the standard radiologic modality, while MRI remains controversial
Einerson et al. (AJOG 2018) sought to determine if MRI contributes to the sonographic diagnosis of Placenta Accreta Spectrum Disorder
METHODS:
Retrospective cohort study
Participants
Patients undergoing both ultrasound and MRI during 2nd and 3rd trimesters
Placenta Accreta Spectrum Disorder suspected (ultrasound or risk factors)
Ultrasound risk factors
Numerous echolucent placental lacunae | Loss of a normal retroplacental hypoechoic space | Loss of detectable myometrium | Bladder wall irregularity | Presence of abnormal subplacental vascularity
Other clinical risk factors (if no suggestive US findings) included
History of endometrial ablation or cavity-entering myomectomy | ≥3 cesarean deliveries in the setting of placenta previa | Suboptimal visualization of the placenta by US
MRI decision left to MFM/surgical and radiology providers
Diagnostic accuracy was verified by surgical and histopathologic diagnosis at the time of delivery
Primary outcome
Change in diagnosis from sonographic interpretation that could alter clinical management
Secondary outcomes
Correlation of radiologic diagnoses with surgical and histopathologic diagnosis
RESULTS:
78 patients were included
Diagnosis that could alter clinical management occurred in 36% of cases
MRI correctly
Changed diagnosis in 19%
Confirmed diagnosis in 44%
MRI incorrectly
Changed diagnosis in 17%
Confirmed diagnosis in 21%
MRI was not more likely to change a diagnosis in the 24 cases of posterior and lateral placental location compared to anterior location (33% vs 37%, P = .84)
MRI resulted in overdiagnosis in 23% and in underdiagnosis in 14% of all cases
In 14 severe Placenta Accreta Spectrum Disorder (percreta) cases, MRI altered only 2 diagnoses, both downgraded
One was a correct downgrade to Placenta Accreta Spectrum Disorder (accreta and increta) and the other was an incorrect downgrade
PPV for severe Placenta Accreta Spectrum Disorder
MRI: PPV 61% (95% CI, 0.41–0.78)
Ultrasound: PPV 73% (95% CI, 0.45–0.91)
Proportion of accurate diagnoses with MRI did not improve over time despite increasing volume and increasing numbers of changed diagnoses
CONCLUSION:
The addition of MRI to the assessment of Placenta Accreta Spectrum Disorder can often lead to an incorrect diagnosis
The authors advise that MRI should not be used routinely as an adjunct to ultrasound in the diagnosis of Placenta Accreta Spectrum Disorder
Latest SMFM Guidelines: Third Trimester Bleeding Between 34w0d and 36w6d Gestation
SUMMARY:
SMFM provides guidance on the management of patients who present with bleeding in the late preterm period (34w0d to 36w6d). The following are the key highlights and recommendations:
Placenta Previa
Stable and no other obstetric complications: Deliver between 36w0d to 37w6d (Grade1B)
Mild late preterm bleeding with 1 or more prior bleeding episodes that occurred <34 weeks of gestation: Consider delivery due to risk of recurrent bleeding
Mild bleeding 34 to 35 weeks with resolution by time of evaluation: Management is less clear
Do not perform routine cervical length screening to determine who will bleed in late preterm period as data in limited on appropriate management (Grade 2C)
Placenta Accreta
Definition: Abnormal trophoblast infiltration beyond the fibrinoid Nitabuch layer
Placenta increta: Placenta invades myometrium
Placenta percreta: Placenta invades beyond the myometrium
Incidence: <1% (in absence of placenta previa unless > 5 prior cesareans
Risk factors
Placenta previa and previous cesarean (most common)
Uterine surgery | Advanced maternal age | Smoking | Multiparity
Stable: Deliver between 34 to 37 weeks (Grade 1C)
If patient is stable, it is reasonable to briefly delay delivery to coordinate requisite multidisciplinary team
ACOG/SMFM recommendations (2019)
Delivery for suspected accreta, increta or percreta at 34w0d to 35w6d
Vasa Previa
Definition: Placental implantation that overlies or abuts the internal cervical os
Presentation: Painless bleeding
Incidence
Seen in 1 to 4% of second trimester ultrasound exams
10 to 20% of previas diagnosed at 20 weeks gestation will remain a previa in the late 3rd trimester
Stable: Deliver between 34 to 37 weeks (Grade 1C)
Placental Abruption
Definition: Placental separation, either partial or complete, prior to delivery
No clinical trials regarding ideal timing for delivery
Stable with high clinical index of suspicion: Delivery in late preterm or early term (expert opinion)
Diagnosis unclear, minimal bleeding, both mother and fetus stable: Delivery may be delayed with close surveillance and ongoing fetal testing
Active bleeding: Delivery as with any other active hemorrhage case
KEY POINTS:
Delivery Considerations
If patient actively bleeding, delivery is indicated if the following are present
Significant vaginal bleeding
Abnormal laboratory results including such as acute anemia or coagulopathy
Abnormal fetal heart tracing
Maternal status unstable
If actively hemorrhaging, do not delay delivery for purpose of administering antenatal corticosteroids (Grade 1B)
Do not perform fetal lung maturity testing in late preterm period to guide management if there is an indication for delivery (Grade 1B)
Administer antenatal corticosteroids if (Grade 1A)
Delivery expected within 7 days
Gestational age is between 34w0d to 36w6d
Antenatal corticosteroids have not previously been administered
Cesarean section for placenta previa, vasa previa or accreta
For other clinical scenarios, vaginal delivery may be appropriate if
No contraindication for vaginal delivery
Fetal status is stable
Small amount of late preterm bleeding that has resolved by the time the patient presents may be treated expectantly if the following conditions met (no evidence-based recommendations currently available)
Both mother and fetus stable
Absence of active bleeding or contractions
Patient lives close to the hospital
Ultrasound Evaluation
Perform ultrasound exam to evaluate placental location prior to digital vaginal exam
Placental previa: Use transvaginal ultrasound
Vasa previa: Pulsed-wave Doppler may help identify a fetal arterial vessel (with FH rate) or fetal vessels with venous flow
Placenta accreta: Ultrasound can be used, but sensitivity (89 to 92%) and specificity (92 to 97%) less than that of placenta previa and vasa previa
Placental abruption: Use clinical suspicion/judgement to determine management as ultrasound can miss this diagnosis in 20 to 50% of the cases
MRI in women who are actively bleeding is not recommended
Laboratory Evaluation
Depends on clinical status and may include
CBC and platelets
Type and cross
Coag studies: PT/PPT/INR/fibrinogen
If transfusion likely: BUN, Cr and lytes
Wall clot test
Place blood in plain (red top) tube
Normal expectation is clot within 6 min
Rh negative patient
Assess maternal-fetal hemorrhage
Quantitative rosette test
Qualitative Kleihauer-Betke stain
Flow cytometry
Administer standard Rh immunoglobulin dose of 300 μg
Increase as needed based on quantitative testing
Initial Stabilization for Delivery
2 large-bore intravenous lines
Obtain results from lab testing above, especially blood type
O-neg blood may need to be identified and prepared in the interim
Crossmatch for an initial 2 to 4 U of blood
Utilize hemorrhage protocol in units where available
Placenta Accreta Spectrum Disorder: Definitions and Management
In normal circumstances, the trophoblast stops invading the uterus when Nitabuch’s layer is reached in the decidua. In cases of accreta, the trophoblast invades the myometrium due to a deficient or damaged Nitabuch’s layer. Placenta accreta occurs within a spectrum of disorders now referred to as ‘Placenta Accreta Spectrum’ (formerly ‘Morbidly Adherent Placenta’)
Placenta Accreta: trophoblasts attach to the myometrium without intervening decidua
Placenta Increta: trophoblasts invade through the myometrium
Placenta Percreta: trophoblasts move through the myometrium and invade beyond the serosa and into surrounding tissues
Clinical Actions:
It is advisable to refer women with clinical or ultrasound risk factors for placenta accreta to a center of excellence for evaluation, confirmation and delivery (Grade 1B – Strong recommendation – Moderate quality evidence)
Arrange for delivery at a level III or IV center with experience if possible
Optimal timing of delivery
Without bleeding or contractions can have a planned cesarean delivery at 34w0d – 35w6d (Grade 1A – Strong recommendation – High quality evidence)
Consider delivery around 34w0d for women with the following (International Society for Abnormally – Invasive Placenta; Grade D recommendation)
History of previous preterm birth | Multiple episodes of small amounts of vaginal bleeding | A single episode of a significant amount of vaginal bleeding | PPROM
Corticosteroids
Administer corticosteroids to all women with suspected accreta if (SMFM recommendation Grade 1A)
Delivery expected within 7 days and meets gestational age criteria
Antenatal corticosteroids have not previously been administered
Do not delay delivery in the setting of active hemorrhage for the purpose of administering antenatal corticosteroids (SMFM recommendation Grade 1B)
Hospitalization vs outpatient care
Outpatient: In the absence of bleeding and any other symptoms or complications, there is limited evidence that hospitalization is of benefit
If outpatient management is elected, there must be a system in place for the patient to rapidly return to the hospital in case of bleeding, contractions or complications
Inpatient: women with preterm labor, PPROM or bleeding are “most likely to benefit” from hospitalization
Hgb levels (FIGO, RCOG and International Society for Abnormally – Invasive Placenta)
If <110 g/L (11 g/dL) before 28 weeks or <105 g/L (10.5 g/dL) after 28 weeks
Work up for anemia and if indicated, begin iron supplementation (oral or intravenous) to optimize levels
Management
In the setting of hemorrhage, the following blood product ratio range is recommended based on data from other surgical specialties (Grade 1A)
Packed RBC:FFP:Platelet = 1:1:1 to 1:2:4
High Risk management can be found in the ‘SMFM Guidelines’ and ‘Obstetric Care Consensus’ and International Society for Abnormally – Invasive Placenta ‘Evidence Based Guidelines’ (see ‘Learn More – Primary Sources’ below)
The International Society for Abnormally – Invasive Placenta does make the following recommendations (Grade D evidence)
Ureteral stents may be used, but insufficient evidence to recommend for routine use with primary benefit likely in the case of percreta
No evidence that routine vertical skin incision is superior to transverse and therefore base decision on
Placental location | Degree of possible invasion suspected | Complication risk | Maternal body habitus | Gestational age | Preference of the surgeon
Avoid placental transection upon uterine incision even if this entails an upper segment or fundal incision
Ultrasound mapping (sterile) “of the exposed uterus should be used, where possible, to locate the placental edge and assist decision making regarding the uterine incision site”
Uterine preservation
Conservative management: Removal of placenta or uteroplacental tissue and no hysterectomy
Focal placental adherence
Followed by repair of uterine defect
Data limited
Expectant management: Placenta left in situ
More extensive adherence
Data limited
ACOG/SMFM obstetric care consensus (2018) states
Conservative management or expectant management should be considered only for carefully selected cases of Placenta Accreta Spectrum after detailed counseling about the risks, uncertain benefits, and efficacy and should be considered investigational (Grade 2C – Weak recommendation – Low quality evidence)
Synopsis:
The incidence of placenta accreta has been increasing from 0.8/1000 in the 1980’s to 3/1000 deliveries. The risk increases with the increasing number of cesarean deliveries. This is especially true for women with placenta previa and prior cesarean sections. Mortality may be as high as 6 to 7%. Maternal complications are primarily the result of massive hemorrhage which can lead to DIC, multi-organ failure, hysterectomy, thromboembolism and death. Neonatal complications are the result of prematurity. The average gestational age at delivery of a pregnancy with Accreta is 34-36 weeks.
Key Points:
If previa is present
3% risk of accreta with the 1st cesarean section
11% risk of accreta at the 2nd cesarean section
40% risk of accreta at the 3rd cesarean section
61% risk of accreta at the 4th cesarean section
67% risk of accreta at the 5th cesarean section
Risk factors
Prior cesarean section
Uterine curettage
Prior myomectomy
Placenta previa
Short inter-pregnancy interval
IVF
Multiparity
Prior pelvic radiation
Endometrial ablation
Maternal smoking
The mainstay of antenatal diagnosis is ultrasound
Note: Absence of ultrasound findings does not mean the patient does not have accreta | Clinical risk factors should be weighted equally compared to sonographic findings (Grade 1A)
First trimester findings include
Cesarean scar pregnancy (risk may approach 100% if pregnancy allowed to continue)
Gestational sac implanted in the lower uterine segment
Irregular vascular spaces in the placental bed
Loss of retroplacental-myometrial zone
Second and third trimester findings include
placenta previa (present in 80% of accreta)
loss of retroplacental-myometrial hypoechoic zone
multiple vascular lacunae
placental villi extension into the myometrium and beyond
interruption of the uterine serosal/ bladder interface
MRI has sensitivities (75%-100%) and specificities (65%-100%) approaching that of ultrasound, but has not been shown to improve the diagnostic accuracy of accreta compared to ultrasound (Grade 1B)
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This educational activity may contain discussion of published and/or investigational uses of agents that are not indicated by the FDA. The planners of this activity do not recommend the use of any agent outside of the labeled indications.
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