This document discusses placental implantation abnormalities (PIAs) such as placenta previa, placenta accreta, vasa previa, and velamentous cord insertion. It covers the incidence, risk factors, ultrasound findings, diagnosis, and complications of these conditions. Key points include:
- PIAs account for 5.6-8.7% of preterm births and are the second leading cause of preterm delivery.
- Risk factors for placenta accreta include previous cesarean sections, placenta previa, and number of prior cesareans.
- Ultrasound criteria can diagnose placenta accreta with 81.1% sensitivity and 98
2. INTRODUCTION
Placental implantation
abnormalities (PIAs) including
placenta previa, placenta accreta, vasa
previa, and velamentous cord
insertion comprise a large group of
disorders that are associated with
significant maternal, fetal, and
neonatal morbidity.
PIAs account for 5.6–8.7% of indicated
preterm deliveries and are the second
3. INTRODUCTION
An increasing emphasis has been placed on
sonographic identification of PIAs, particularly in the
first trimester, as well as the use of MRI as an adjunct
to sonography.
There has been an increase in publications pertaining to cesarean
scar pregnancies as a possible precursor to placenta accreta as
they share a similar pathophysiology
This PRESENTATION will discuss recent advances in the literature
as well as proposed guidelines for the management of PIAs.
4. INCIDENCE
Placenta previa 1:200 pregnancies
Placenta previa accreta
No previous CS 3%
One previous CS 11%
Two previousCS 40%
≥3 previous CS >60%
Vasa previa 1:2000 – 1:6000
When fetal bleeding occurs then the perinatal mortality is >60%
◾ RCOGGreen-topGuideline number 27 January 2011
6. DEFINITION OF PLACENTA PREVIA
Terminology for placenta previa has been confusing. In a recent Fetal
Imaging Workshop sponsored by the National Institutes of
Health , the following classification was recommended:
• Placenta previa—the internal os is covered partially or
completely by placenta. In the past, these were further
classified as either total or partial previa .
•Low-lying placenta—in which the placenta lies
within 2 cm of the cervical os but does not cover it. (Reddy UM
et al 2014)
Vasa praevia describes fetal vessels coursing through the membranes over the internal cervical os and
below
7. ESTABLISHED RISK FACTORS FOR PLACENTA PREVIA
INCLUDE
Intrinsic maternal factors
• Increasing parity
• Advanced maternal age
• Maternal race
Extrinsic maternal factors
• Cigarette smoking
• Cocaine use
• Residence at higher elevation
• Infertility treatments
Fetal factors
• Multiple gestations
• Male fetus
Prior placenta previa
Prior uterine surgery and cesarean deliver
Elevated Prenatal Screening MSAFP Lev
8. A direct relationship exists between number of prior cesarean
deliveries and risk of placenta previa . A linear increase is seen in
placenta previa risk with the number of prior cesarean deliveries
Risk factors for placenta accreta include all of the previous with
the most significant factor being the presence of both a prior
cesarean delivery and placenta previa.
In a large prospective observational cohort in the United States,
women with a placenta previa had a risk of placenta accreta of 3,
11, 40, 61, and 67% for the first, second, third, fourth, and fifth or
more prior cesarean deliveries, respectively [Silver RM, et al
2006]
RISK FACTORS
9. PRIMARY AND SECONDARY UTERINE
PATHOLOGIES ASSOCIATED WITH PLACENTA
ACCRETA
Primary Uterine
Pathology
Major uterine anomalies
Adenomyosis
Submucous uterine
fibroids
Myotonic dystrophy
Secondary Uterine
Pathology
Cesarean delivery
Uterine curettage
Manual removal of the
placenta
Cavity-entering myomectomy
Hysteroscopic surgery
(endometrial resection)
In vitro fertilization
10. Risk factors for vasa previa based on a systematic review include[ Ruiter
et al 2016]
Velamentous cord insertion,
Bilobed or succenturiate placenta,
Second-trimester placenta previa,
Umbilical cord insertion in the lower third of the uterus
at the time of the first-trimester ultrasound,
Assisted reproductive technologies.
RISK FACTORS
11. NEWLY IDENTIFIED RISK FACTORS
A recent study by Downes et al. demonstrated the significance of prior delivery
history on the risk of developing placenta previa. In this retrospective cohort study
of the first two singleton deliveries, a previous prelabor cesarean
delivery was associated with a greater than two-fold increased risk of placenta
previa in the second delivery compared with previous vaginal delivery [adjusted
odds ratio (aOR) 2.62, 95% confidence interval (CI) 1.24–5.56].
However, previous intrapartum cesarean delivery was not associated
with an increased risk of placenta previa (aOR 1.22, 95% CI 0.68–2.19).
This draws attention to the potential importance of presence versus absence of
labor in relation to cesarean delivery for the development of future placenta
previa.
12. In addition, in a large population-based cohort study of AIP in
Nordic countries, Thurn et al[2016] confirmed the major risk
factors of placenta previa and prior cesarean delivery.
Placenta previa was reported in 49% of all cases, conferring an
absolute risk of 2–10%, and was associated with an odds ratio of
170–640.
The risk of AIP was increased seven-fold after one prior cesarean
delivery [odds ratio (OR) 6.6, 95% CI 4.4–9.8] to 56-fold after
three or more cesarean deliveries (OR 55.9, 95% CI 25–110).
Importantly, this study also identified a new risk factor for AIP,
which was previous postpartum hemorrhage (six-fold
increased risk; OR 6.5, 95% CI 3.7–10.9).
NEWLY IDENTIFIED RISK FACTORS
13. MATERNAL, FETAL, AND NEONATAL
COMPLICATIONS
Clinical complications of PIAs are divided into maternal, fetal,
and neonatal.
Maternal complications are largely secondary to hemorrhage
and other surgical morbidities. .
Maternal complications of placenta accreta include
hysterectomy, injury to other organs, blood
transfusion,disseminated intravascular coagulation (DIC),
infection, and death.
Fetal and neonatal complications are related to complications of
preterm birth(PTB) and small for gestational age (SGA) as
well as fetal–neonatal hemorrhage secondary to ruptured fetal
vessels in cases of vasa previa
14. Predictors for emergent delivery in women with placenta
previa include
a history of cesarean delivery,
antepartum bleeding,
and the need for antepartum blood transfusion;
a direct relationship exists between number of episodes
of antepartum bleeding and the risk for emergent
MATERNAL, FETAL, AND NEONATAL
COMPLICATIONS
15. DIAGNOSIS
PIAs are usually identified by ultrasound in the
second-trimester fetal anatomic survey performed
between 18 and 22 weeks, with the exception of
cesarean scar pregnancies which may be identified in
the first trimester.
in a prospective cohort study evaluating the distance between the placental edge and
the internal os, a placenta–cervix distance cutoff of 4.2 cm was 93.3% sensitive and
76.7% specific for the detection of placenta previa with a 99.8% negative predictive
value at a screen-positive rate of 25.0%. A cutoff of 2.8 cm was 86.7% sensitive,
90.5% specific with a 99.6% negative predictive value at a screen-positive rate of
11.4%
[Quant HS, et al 2014].
17. ULTRASOUND CRITERIA FOR DIAGNOSIS OF PLACENTA
ACCRETE WERE AS FOLLOWS:
Greyscale:
● loss of the retroplacental sonolucent zone
● irregular retroplacental sonolucent zone
● thinning or disruption of the hyperechoic serosa–bladder interface
● presence of focal exophytic masses invading the urinary bladder
● abnormal placental lacunae.
Colour Doppler:
● diffuse or focal lacunar flow
● vascular lakes with turbulent flow (peak systolic velocity over 15 cm/s)
● hypervascularity of serosa–bladder interface
● markedly dilated vessels over peripheral subplacental zone.
Three-dimensional power Doppler:
● numerous coherent vessels involving the whole uterine serosa–bladder junction (basal view)
● hypervascularity (lateral view)
●inseparable cotyledonal and intervillous circulations, chaotic branching, detour vessels (lateral
view)
18. PLACENTA ACCRETA
The accuracy of ultrasound in antenatal diagnosis of placenta
accreta was described in a prospective trial of 314 women with
placenta previa in which 37 were confirmed to have a placental
attachment disorder at delivery .
(Pilloni E et al 2016)
The following ultrasound criteria were evaluated: loss or irregularity
of the retroplacental clear zone, thinning or interruption of the
uterine serosa–bladder interface, loss of the vascular arch parallel to
the basal plate and/or irregular intraplacental vascularization,
myometrial thickness less than 1 mm, and turbulent placental
lacunae. The presence of at least two criteria provided a sensitivity
of 81.1% and specificity of 98.9% for the diagnosis of placenta
accreta.
19. PLACENTA ACCRETA INDEX
a Placenta Accreta Index was formulated by Rac et
al.(2015)assessing the ultrasound parameters of
loss of retroplacental clear zone,
irregularity and width of uterine–bladder interface,
smallest myometrial thickness,
presence of lacunar spaces,
and bridging vessels.
All parameters were associated with placental invasion
and each parameter was weighted to create a nine-point
scale (Placenta Accreta Index) corresponding to the
prediction of individual patient risk for MAP.
20. Loss of retro placental
clear space
Echolucent line that
sonographically represents
vascular decidua basalis and
extends entire length of
placenta. The middle arrow
points to area of obliteration
from invading placenta and
smaller 2 arrows show normal
Placenta Accreta Index. Am J O
rb
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l clear space.
21. Irregularity of
uterine-bladder
interface
Arrows point to dot-and-dash
appearance of echogenic uterine-
bladder interface.
This irregularity is caused by
abnormal bridging vasculature that
is easily seen with Doppler
velocimetry.
Placenta Accreta Index. Am J Obstet Gynecol 2015.
22. Thinning of uterine-bladder
interface
Normally thick and echogenic
interface is replaced by
ingrowth of morbidly adherent
placenta (arrows).
Placenta Accreta Index. Am J Obstet Gynecol 2015.
23. Smallest myometrial
thickness
Retro placental myometrium is thin as result of
abnormal ingrowth of placenta. Smallest
myometrial thickness in sagittal plane is
measured. Measurement of smallest thickness
is <1 mm.
24. Placenta lacunar
spaces
Sonolucent areas throughout placenta that
vary in size and shape and give placenta
“Swiss cheese” appearance. This patient
had >6 lacuna (arrows). They were large
and very bizarre-appearing throughout,
consistent with grade-3+ lacunae.
Additionally, no myometrium is present
between placenta and uterine-bladder
interface
Placenta Accreta Index. Am J Obstet Gynecol 2015
25. Bridging vessels
Doppler color mapping demonstrates
abnormal vasculature that bridges from
placental mass to uterine-bladder
interface and sometimes beyond (arrows).
Placenta Accreta Index. Am J Obstet Gynecol 2015
26. Parameter
a
Value
≥2 cesarean deliveries 3
Lacunae
Grade 3 3.5
Grade 2 1
Sagittal smallest myometrial thicknessb
≤1 mm 1
<1 but ≥3 mm 0.5
>3 but ≤5 mm 0.25
Anterior placenta previa
c
1
Bridging vessels 0.5
Value of each parameter is added together to generate Placenta Accreta Index score
Rac. Placenta Accreta Index. Am J Obstet Gynecol 2015.
A If parameter is not present, then value is 0
bMeasured in sagittal plane
C If any portion of placenta is anterior.
28. FIRST-TRIMESTER FINDINGS
In a retrospective study evaluating first-trimester sonographic findings of MAP, 39 patients
were identified with a history of prior cesarean delivery who had placenta previa or low-lying
placenta diagnosed on third-trimester sonography and who had first-trimester sonographic
images available for review. The only sonographic finding that was
predictive of MAP was the smallest anterior myometrial thickness
measured in the sagittal plane, which was significantly smaller in
pregnancies complicated by MAP at delivery compared with those
without MAP (4.1 versus 7.4 mm, P = 0.01).
The number of prior cesarean deliveries was also significantly
associated with placental invasion.
Combining these two variables yielded an area under the receiver
operating characteristic curve of 0.94 (95% CI 0.87–1.00),
suggesting that in women with persistent placenta previa or low-
lying placenta and prior cesarean delivery, the smallest anterior
myometrial thickness on first-trimester ultrasound improved
29. Gestational sac
implantation in the
lower segment in a
patient with prior
cesarean section.
Note the presence of
multiple irregular
vascular spaces within
the placental bed
(arrows).
This pregnancy ended
placenta percreta. GS,
E.M. Berkley, A.Z. AbuhamadThe prenatal diagnosis of placen
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Ultrasound Med, 32 (2013), pp. 1345–1350
30. CESAREAN SCAR PREGNANCY
a cesarean scar pregnancy is thought to be a precursor to
placenta accreta [Timor-Tritch et al 2016] and can be
identified sonographically by the presence of a gestational
sac implanted into the uterine window of a prior
hysterotomy. Other criteria include an ‘empty’ uterine
fundus and cervical canal with clearly demonstrated
endometrium.
In differentiating between a cesarean scar pregnancy and a
normal intrauterine pregnancy, Timor-Tritsch et al. found that the
location of the center of the gestational sac relative to the midpoint
axis of the uterus can be used, with a low gestational sac relative to
the midpoint of the uterus at 5–10 weeks identifying most cases of
cesarean scar pregnancies.
31.
32. Cesarean section scar
implantation of a
gestational sac.
Note the location of
the gestational sac
imbedded into the
cesarean section scar
at the level of the
cervical internal os
(arrow) at the base of
the bladder (B).
33. MRI DIAGNOSIS
In a retrospective study of women at high risk for MAP who underwent MRI evaluation, MRI
features associated with pathologically confirmed placenta accreta included increased
vascularity, dark T2 bands, uterine bulging, thin (< 2 mm) or indistinct
myometrium, and loss of the dark T2 interface. When seen in isolation,
each of these features was sensitive but not specific; however, the
presence of two or more criteria added specificity to the diagnosis of
placental invasion on MRI.
D’Antonio et al[2014] performed a systematic review and meta-analysis evaluating the
predictive accuracy of MRI for the diagnosis of invasive placental disorders, the depth and
topography of placental invasion, and comparing the use of MRI to ultrasound. Of 18 studies
identified, the use of MRI conferred 94.4% sensitivity and 84.0% specificity in detecting invasive
placental disorders, 92.9% sensitivity and 97.6% specificity in assessing depth of placental
invasion, and 99.6% sensitivity and 95.0% specificity in assessing topography of placental
invasion. Individual MRI signs – uterine bulging, heterogeneous signal intensity, dark
intraplacental bands on T2 weighted sequences, focal interruption of the myometrium,
and tenting of the bladder – showed good predictive accuracy in the diagnosis of
invasive placental disorders. This suggests that MRI offers high accuracy in diagnosing
invasive placental disorders and comparable predictive accuracy compared with
34. A, SAGITTAL MAGNETIC RESONANCE IMAGE (MRI)
WITH THE FETUS (F) IN VERTEX POSITION AT 25
WEEKS' GESTATION. THE PLACENTA (P) IS ANTERIOR
AND LOW LYING WITH LOSS OF THE NORMAL
MYOMETRIAL DARK SIGNAL.. PROMINENT VESSELS
( ARROW ) BETWEEN THE UTERUS AND THE
BLADDER (B) ARE CONCERNING FOR INVOLVEMENT
OF THE BLADDER WALL BY PLACENTA PERCRETA
B, Axial MRI demonstrates placental tissue (P)
abutting the left posterior aspect of the urinary
bladder (B) with loss of the dark myometrial signal,
preserved on the right side of the placenta ( arrow ).
Findings are suggestive of invasion of the bladder by
placenta percreta. Abnormal placentation was
confirmed on pathologic examination.
35. MANAGEMENT
Referral of all women diagnosed antenatally with PA
to a tertiary care center with experience in the
management of PA and use of a multidisciplinary care
team is therefore recommended by professional
organizations, including the
American College of Obstetricians and Gynecologists
(ACOG), the American Society of Anesthesiologists
(ASA),
the Royal College of Anesthetists (RCA),
36. PREPARATION FOR SURGICAL MANAGEMENT OF PLACENTA ACCRET
INTERVENTION COMMENT
center
Treatment at a referral Availability of multidisciplinary team that includes pelvic surgeons,
anesthesiologist, vascular/trauma surgeons, interventional radiologist,
neonatologist
Preoperative imaging Ultrasound evaluation of placenta
Timing of delivery Approximately 34 weeks (with placenta previa)
Delivery location Consider main OR or have all available equipment on labor and delivery. OR
staff must be trained in advanced pelvic surgical procedures.
Anesthesia Consider general anesthesia.
Vascular access Central line, arterial line
Ureteral stents Consider retrograde ureteral stent placement prior to laparotomy.
Cell salvage Cell salvage availability
Rapid infusion Availability of rapid infusion device
Interventional
radiology
Consider catheter placement for uterine artery embolization and/or balloon
occlusion catheter placement.
Blood bank Packed red cells (10-20 U), fresh frozen plasma (10-20 U), platelets (12 U)
37. MANAGEMENT
Guidelines for the delivery of PIAs are universally
preterm in order to avoid catastrophic complications of
labor.
As such, delivery recommendations set out by
professional societies for prenatally diagnosed placenta
previa, placenta accreta, and vasa previa are 36–37 weeks
, 34–35 weeks , and 34–36 weeks gestation , respectively.
However, more recent clinical opinions and expert reviews
are suggesting to individualize care in order to delay
delivery patients who are deemed clinically stable in order
to decrease the risks associated with prematurity.( D
Antinio et al 2014)
38. PATIENT INFORMATION
Risk of major haemorrhage 1:5
Risk of hysterectomy 1:10
Return to theatre rate 75:1000
Bladder injury 23:1000
Depends on the clinical scenario
For major placenta previa…
▪
▪
▪
▪
For previa and previousCS…
▪ Risk of hysterectomy is 1:3
For placenta previa accreta…
▪ Hysterectomy “very likely”
◾ RCOGGreen-topGuideline number 27 January 2011
39. In a review by Vintzileos et al proposed management
strategies are
.
outlined for PIAs depending on cervical
length, distance between internal cervical os and placenta,
and placental edge thickness.
Proposed algorithms are provided in Figs 1, 2, 3, and 4,
with the goal to identify patients who may be safely
expectantly managed to term and those who may be at
greater risk and require inpatient monitoring or earlier
delivery
( Vintzileos et al 2015)
44. ◾ Surgical tips
▪ Use all available techniques for
continuing bleeding after removal of a
placenta previa e.g. Oxytocics, direct
suture, B-Lynch suture, ut. artery
embolisation hysterectomy etc.
▪ Try to avoid section through a placenta
accreta
▪ Do not attempt to remove a morbidly
adherent placenta
▪ Hysterectomy with placenta intact or
▪ Leave the placenta behind when uterine
conservation desired
45. CONCLUSION
Established risk factors such as the coexistence of placenta previa with a history
of prior cesarean delivery increasing the risk for placenta accreta, and novel risk
factors for placenta previa such as previous postpartum hemorrhage or prelabor
cesarean
Various imaging modalities were discussed as well including ultrasound
and MRI with different parameters based on trimester raising the suspicion
for placental invasion
Established recommendations for delivery are universally
preterm in order to avoid potentially catastrophic complications
of labor.
Current directions are focusing on individualizing care based
on ultrasound markers such as cervical length, distance
between the internal cervical os and placenta, and placental
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Shriver National Institute of Child Health and Human Development, Society of Maternal-
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