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DOI 10.1515/jpm-2012-0219
J. Perinat. Med. 2012; aop
Jacques Balayla * and Helen Davis Bondarenko
Placenta accreta and the risk of adverse maternal
and neonatal outcomes
1)
Abstract
Objective: Placenta accreta is an increasingly prevalent
and potentially dangerous complication of pregnancy.
Although most studies on the subject have addressed the
risk factors for the development of this condition, evidence
on maternal and neonatal outcomes for these pregnancies
is scarce. The objective of the present study is to compile
current evidence with regard to risk factors as well as
adverse outcomes associated with placenta accreta.
Methods: We conducted a complete literature review
using PubMed, MEDLINE, Cochrane Database Reviews,
UptoDate, DocGuide, as well as Google scholar and text-
book literature for all articles on placenta accreta, and any
one of the following keywords: “ risk factors ” , “ maternal
outcomes ” , “ neonatal outcomes ” , “ morbidity ” , and “ mor-
tality ” . Individual case reports were excluded.
Results: We reviewed 34 studies conducted between
1977 and 2012. A total number of 508,617 deliveries were
studied, with 865 cases of confirmed placenta accreta
(average pooled incidence = 1/588). The development of
placenta accreta appears to be most strongly predicted
by a history of cesarean section, low-lying placenta/
previa, in vitro fertilization pregnancy, as well as elevated
second-trimester levels of α -fetoprotein and β -human
chorionic gonadotropin. The most significant maternal
outcomes include the need for postpartum transfusion
due to hemorrhage and peripartum hysterectomy. Mater-
nal mortality remains rare but significantly higher than
among matched, postpartum controls. Important neo-
natal outcomes include preterm birth, low birth weight,
small for gestational age, and reduced 5-min Apgar
scores. Whether the need for neonatal intensive care
unit admission and steroid administration is iatrogenic
and whether an increased risk of perinatal mortality is a
clinically significant and independent outcome remain
controversial.
Conclusion: Although there is a significant shortage of
studies on the subject, it appears that placenta accreta is
associated with adverse maternal and neonatal outcomes,
some of which may be life threatening. Prenatal diagnosis
and adequate planning, particularly in high-risk popula-
tions, may be indicated for the reduction of these adverse
outcomes.
Keywords: diagnosis ; maternal outcomes ; morbidity
and mortality ; neonatal outcomes ; placenta accreta; risk
factors .
1)
Contribution to authorship: Both authors contributed to study
design, acquired and analyzed the data, wrote and reviewed this
article, and approved its submission for publication in its current
form.
*Corresponding author: Dr. Jacques Balayla , Department of
Obstetrics and Gynecology, University of Montreal, Montreal,
Quebec, Canada H3G 1Y6, Tel.: + 1-514-830-7849,
E-mail: jacques.balayla@umontreal.ca
Jacques Balayla and Helen Davis Bondarenko: Faculty of Medicine ,
University of Montreal, Montreal, QC , Canada
Introduction
Abnormal placental implantation occurs when placental
trophoblasts invade into the superficial uterine endome-
trium (placenta accreta), into the myometrium (placenta
increta), or beyond the uterine serosa (placenta percreta).
The pathogenesis is primarily attributed to the defective
decidualization of the implantation site and the absence
of both the decidua basalis and the Nitabuch ’ s layer,
which results in a direct attachment of the chorionic villi
to the myometrium [7, 12, 32] . Placenta accreta occurs more
frequently than placenta increta and percreta. In a pooled
analysis of results from two series of confirmed, abnor-
mally implanted placentas from hysterectomy specimens,
the type and frequency of abnormal placentation were the
following: placenta accreta, 79 % ; placenta increta, 14 % ;
placenta percreta, 7 % [21, 38] .
In the event of placenta accreta, the third stage of
labor is often prolonged and may be complicated by severe
uterine hemorrhage, requiring extensive life-saving sur-
gical interventions such as hysterectomy and manipula-
tion of major pelvic vessels [12] . Massive blood and blood
product transfusions are often the norm, and maternal
morbidity is reported to be high [12] . Numerous risk factors,
such as a current placenta previa, prior uterine surgery,
increased parity, thin decidua, and advanced maternal
age, are alleged to be associated with the development of
this condition. Perhaps no greater risk factor exists than a
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Balayla and Davis Bondarenko, Placenta accreta and the risk of adverse maternal and neonatal outcomes
history of cesarean section, which estimates a 2-fold risk
among those with a prior cesarean section and an 8-fold
risk in women with two or more prior cesarean sections
[38] . Having a low-lying placenta/previa is also reported to
be a critical risk factor [5, 38] . Given the rising incidence
of cesarean sections over the last several decades [37, 38] ,
cases of placenta accreta have been on the rise as well and
are now estimated at 1 in every 530 pregnancies [11] .
Although most studies on the subject have addressed
the risk factors for its development, evidence on mater-
nal and neonatal outcomes of pregnancies complicated
by placenta accreta is scarce. Previous studies assessing
the association between placenta accreta and perinatal
outcomes have yielded inconsistent results [11, 21, 38] .
Therefore, through a complete review of the literature, the
objectives of the present study are to review the reported
risk factors for placenta accreta and to elucidate whether
adverse maternal and neonatal outcomes are associated
with this condition.
Methods
To identify the risk factors and outcomes associated with the devel-
opment of malplacentation relating to trophoblastic invasion, we
conducted a literature review using PubMed, MEDLINE, Cochrane
Database Reviews, UptoDate, DocGuide, as well as Google scholar
and textbook literature for all articles on placenta accreta. The search
strategy was developed to comprise searches both for keywords and
medical subject headings under existing database organizational
schemes. The following MeSH terms were primarily emphasized: “ pla-
centa accreta ” , “ placenta increta ” , “ placenta percreta ” , “ risk factors ” ,
“ maternal outcomes ” , “ neonatal outcomes ” , “ morbidity ” , and “ mor-
tality ” . Additional articles were identi ed by reviewing bibliographic
references in the articles identi ed through the initial search ndings.
We searched the reference lists of all other relevant reviews and stud-
ies and retrieved all other articles that complimented our topic. If a
paper reported ndings on di erent degrees of placental invasion, an
emphasis was placed on those ndings relating to placenta accreta. No
language restriction was considered. Given the rarity of this condition,
studies were not limited by design or number of reported patients. In-
dividual case reports were excluded. The total review retrieved 34 stud-
ies, published between 1977 and 2012, that met the inclusion criteria.
The number of studies on maternal risk factors (n = 13) was suf-
cient to select those whose ndings are reached through logistic
regression and reported as odds ratios (ORs) (n = 8) (Table 1 ). Among
these, comparison is easily attainable. In Tables 2 and 3 , the ndings
are reported in their original, heterogeneous form, where trends are
nonetheless evident.
Results
A total number of 508,617 deliveries were studied, with
865 cases of confirmed placenta accreta (average pooled
incidence = 1/588). The development of placenta accreta
appears to be most strongly predicted by a history of
previous cesarean section as well as by a low-lying pla-
centa/placenta previa (Table 1). Less evidently, elevated
second-trimester maternal serum levels of α -fetoprotein
(AFP) and free β -human chorionic gonadotropin ( β -hCG)
beyond 2.5 multiples of the median (MoM), as well as in
vitro fertilization (IVF) pregnancies, appear to be strong
predictors of the presence of placenta accreta as well.
Advanced maternal age and female fetal gender appear to
be less important risk factors than those mentioned above
but statistically significant ones nonetheless. A history of
uterine surgery other than cesarean section, but including
curettage, as well as the presence of uterine leiomyomas
during pregnancy, does not appear to be strongly associ-
ated with malplacentation (Table 1). Whether increased
parity and gravidity are true risk factors remains conten-
tious, likely due to the confounding variable of a history
of cesarean section, which may increase the risk of subse-
quent placenta accreta.
Once a clinical or pathologic diagnosis of malpla-
centation has been made, important maternal outcomes
include significant hemorrhage, the need for emergency
hysterectomy, and a mildly increased risk of mortality
compared with age-matched controls without malplacen-
tation (Table 2). It appears that blood transfusions may be
required in anywhere from 20 % to 70 % of cases. Similar
numbers are reported for postdelivery hysterectomy. One
study reports the need for postpartum uterine curettage to
be as high as 54 % among those who did not have a cesar-
ean hysterectomy [37] .
The reported neonatal outcomes included perinatal
mortality, preterm delivery, birth weight, 5-min Apgar < 7,
neonatal intensive care unit (NICU) admission, steroid
administration, neonatal asphyxia, and hypoxia (Table
3). Placenta accreta is most strongly associated with
preterm birth, low-birth weight, small for gestational age,
and reduced 5-min Apgar scores. The results are mixed on
whether the need for NICU admission and steroid admin-
istration and the increased risk of perinatal mortality are
clinically significant, independent outcomes.
Discussion
Placenta accreta is an increasingly common and poten-
tially dangerous obstetric event that is most often diag-
nosed after the second stage of labor is completed. Unlike
incomplete abortions with subsequent retained prod-
ucts of conception, placenta accreta is characterized by
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Balayla and Davis Bondarenko, Placenta accreta and the risk of adverse maternal and neonatal outcomes
3
Risk factor Study Year Country Sample size (incidence
of placenta accreta)
Results: OR ( % CI) P-value
Previous cesarean Wu etal. [] USA n = , (/) : . (. – .) .
≥ : . (. – .) < .
Gielchinsky etal. [] Israel n = , (/) . (. – .) –
Hung etal. [] Taiwan n = (/) : . (. – .) .
≥ : . (. – .) .
Kennare [] Australia n =
a
. (. – .) –
Advanced maternal age ( > years) Wu etal. [] USA n = , (/) . (. – .) < .
Gielchinsky etal. [] Israel n = , (/) % of all cases –
Hung etal. [] Taiwan n = (/) . (. – .) < .
Dare etal. [] Nigeria n =
a
. (. – .) .
Fitzpatrick etal. [] UK n =
a
. (. – .) –
High parity-gravidity Gielchinsky etal. [] Israel n = , (/) . (. – .) –
Hung etal. [] Taiwan n = (/) Gravidity
: . (. – .) .
≥ : . (. – .) < .
Parity
: . (. – .) .
History of uterine curettage Gielchinsky etal. [] Israel n = , (/) % of all cases –
Hung etal. [] Taiwan n = (/) – : . (. – .) .
≥ : . (. – .) < .
Placenta previa/low-lying placenta Wu etal. [] USA n = , (/) . (. – .) < .
Gielchinsky etal. [] Israel n = , (/) . (. – .) –
Hung etal. [] Taiwan n = (/) . (. – .) < .
Dare etal. [] Nigeria n = . (. – .) < .
Fitzpatrick etal. [] UK n =
a
. (. – .) –
Second-trimester AFP and β -hCG > . MoM Hung etal. [] Taiwan n = (/) AFP: . (. – .) < .
β - hCG: . (. – .)
Dreux etal. [] France n =
a
AFP: . (. – .) < .
β - hCG: . (. – .)
Previous uterine surgery Hung etal. [] Taiwan n = (/) . (. – .) .
Fitzpatrick etal. [] UK n =
a
. (. – .) –
Uterine fibroids Hung etal. [] Taiwan n = (/) . (. – .) .
Fetal male gender Hung etal. [] Taiwan n = (/) . (. – .) .
Khong etal. [] Australia n = , (/) . (. – .) –
IVF pregnancy Fitzpatrick etal. [] UK n =
a
. (. – .) –
Table 1 Indicators and risk factors for the development of placenta accreta.
a
Number of cases where incidence was not available.
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Balayla and Davis Bondarenko, Placenta accreta and the risk of adverse maternal and neonatal outcomes
Outcome Study Year Country Sample size (incidence
of placenta accreta)
Findings P-value
Hemorrhage and transfusion Warshak etal. [] USA n =
a
Average estimated blood loss between ± .
and ± . mL depending on time of diagnosis
.
Wax etal. [] USA – . % required postpartum transfusion < .
Gielchinsky etal. [] Israel n = , (/) . % required postpartum transfusion –
Makhseed and Moussa [] Kuwait n = , (/,) . % required postpartum transfusion –
Breen etal. [] USA n =
a
. % developed postpartum hemorrhage –
Umezurike etal. [] Nigeria n = (/) Median blood loss: mL –
Median transfusion amount: U
Kupferminc etal. [] USA n =
a
Average blood loss: ± mL < .
Blood transfusion: . ± . U < .
Armstrong etal. [] Australia n =
a
Mean intraoperative blood loss of mL –
Hysterectomy Wax etal. [] USA – . % vs. % for matched controls < .
Gielchinsky etal. [] Israel n = , (/) / (. % ) –
Makhseed and Moussa [] Kuwait n = , (/,) . % of cases –
Read etal. [] USA n = , (/) . % of cases –
Breen etal. [] USA n =
a
. % of cases –
Ota etal. [] Japan n = (/) . % of cases –
Umezurike etal. [] Nigeria n = (/) . % of cases –
Sfar etal. [] Tunisia n = , (/) . % of cases –
Armstrong et al [] Australia n =
a
. % of cases –
Belfort [] USA – OR . ( % CI . – .) < .
Mortality Gielchinsky etal. [] Israel n = , (/) / (. % ) –
Makhseed and Moussa [] Kuwait n = , (/,) / (. % ) < .
Read etal. [] USA n = , (/) / (. % ) –
Breen etal. [] USA n =
a
/ (. % ) –
Umezurike etal. [] Nigeria n = (/) / (. % ) –
Sfar etal. [] Tunisia n = , (/) / (. % ) –
Armstrong etal. [] Australia n =
a
/ (. % ) –
Uterine curettage required Wax etal. [] USA – . % vs. % for matched controls < .
Table 2 Maternal outcomes of placenta accreta.
a
Number of cases where incidence was not available.
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Balayla and Davis Bondarenko, Placenta accreta and the risk of adverse maternal and neonatal outcomes
5
Outcome Study Year Country Sample size (incidence
of placenta accreta)
Findings P-value
Perinatal mortality Seet etal. [] USA n = , (/) Superficial invasion: / (. % ) .
Deep invasion: / (. % )
Makhseed and Moussa [] Kuwait n = , (/,) / (. % ) < .
Read etal. [] USA n = , (/) / (. % ) –
Breen etal. [] USA n =
a
/ (. % ) –
Umezurike etal. [] Nigeria n = (/) / (. % ) –
Sfar etal. [] Tunisia n = , (/) / (. % ) –
Preterm delivery Seet etal. [] USA n = , (/) Superficial invasion: / (. % ) .
Deep invasion: / (. % )
Gielchinsky etal. [] Israel n = , (/) OR . ( % CI . – .) < .
Sfar etal. [] Tunisia n = , (/) / (. % ) –
Hung etal. [] Taiwan n = (/) OR . ( % CI . – .) .
Fitzpatrick etal. [] UK n =
a
OR . (. – .) –
Low birth weight/small for gestational age Seet etal. [] USA n = , (/) Low birth weight ( – g) .
Superficial invasion: / (. % )
Deep invasion: / (. % )
Very low birth weight ( – g) .
Superficial invasion: / (. % )
Deep invasion: / (. % )
Gielchinsky etal. [] Israel n = , (/) Small for gestational age < % : OR .
( % CI . – .)
< .
Small for gestational age < % : OR .
( % CI . – .)
Wax etal. [] USA – ± vs. ± g for matched
controls
.
-min Apgar < Seet etal. [] USA n = , (/) Superficial invasion: / (. % ) .
Deep invasion: / (.) %
Wax etal. [] USA – . % vs. . % for matched controls .
NICU Admission Seet etal. [] USA n = , (/) Superficial invasion: / (. % ) .
Deep invasion: / (. % )
Warshak etal. [] USA n =
a
Between % and % admission rate
depending on time of diagnosis
.
Steroid administration Warshak etal. [] USA n =
a
Between % and % depending on time
of diagnosis
≤ .
Neonatal asphyxia Ota etal. [] Japan n = (/) / (. % ) –
Hypoxia secondary to severe hemorrhage Sfar etal. [] Tunisia n = , (/) / (. % ) –
Table 3 Neonatal outcomes associated with placenta accreta.
a
Number of cases where incidence was not available.
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Balayla and Davis Bondarenko, Placenta accreta and the risk of adverse maternal and neonatal outcomes
an incomplete or total retention of the placenta, which
remains embedded within the uterine musculature. This
phenomenon results in a lack of placental expulsion and a
prolonged third stage of labor that often requires medical,
surgical, and pharmacologic interventions to resolve.
Despite its relatively low incidence and often-complex
diagnosis, epidemiologic data have been consistent in
establishing the risk factors associated with this condi-
tion [21, 25] . However, previous studies assessing the asso-
ciation between placenta accreta and perinatal outcomes
have yielded inconsistent results [11, 21, 38] . As such, this
study compiles the current evidence in the literature with
regard to the aforementioned risk factors and outcomes of
placenta accreta, which are well described in Tables 1 – 3.
Risk factors
The goal of elucidating risk factors for placenta accreta
serves multiple purposes. It allows obstetric care provid-
ers to have a better understanding of the pathophysiology
of this condition, it aids in diagnosis, and it allows for
patients to be counseled during pregnancy, especially if
the need for predelivery planning exists. This is an impor-
tant step, as most cases of placenta accreta have no pre-
ceding symptoms, thus a higher degree of suspicion for
its early diagnosis should rely on known risk factors [12] .
With regard to the risk factors, a history of cesarean
section is reported as an important predictor of the future
development of placenta accreta (Table 1). A report from
the National Institutes of Health [22] states that 0.3 % , 0.6 % ,
and 2.4 % of those having had one, two, and three previous
cesarean births, respectively, will develop placenta accreta
in subsequent pregnancies. It is theorized that the hyster-
otomy scar subsequent to the operation may damage the
decidual interface at the implantation site, thus allowing
for direct insertion of the placenta into the myometrium in
subsequent gestations [32] . Similarly, a low-lying placenta/
previa may be predictive of placenta accreta. This may
stem from a similar notion of a “ defective ” endo-myome-
trial interface over the internal os, which does not allow
for normal placental implantation to occur. This effect is
magnified when both risk factors are combined, that is,
when placenta previa follows a history of cesarean section
[5, 21, 31] . Although the cause remains unknown, several
concepts have been proposed to explain the cause of
abnormal implantation in placenta accreta. These include
a primary defect of the trophoblast function, a secondary
basalis defect due to a failure of normal decidualization,
and more recently, an abnormal vascularization and tissue
oxygenation of the scar area [15] .
Other important risk factors may only be elucidated
during pregnancy and may be independent of obstetric
history. Indeed, second-trimester maternal serum levels
of β -hCG and AFP may help to improve the prenatal detec-
tion of placenta accreta [7] . Several series and case reports
have reported an association between placenta accreta
and otherwise unexplained elevations in second-trimes-
ter concentration of maternal serum AFP ( > 2 or 2.5 MoM)
[14, 18, 40] . However, this is an inconsistent finding and
is not useful by itself in establishing a definitive diag-
nosis. Additionally, a normal maternal serum AFP level
does not exclude a diagnosis of malplacentation. In one
report, only 9 (45 % ) of 20 women with placenta accreta/
percreta/increta had second-trimester maternal serum
AFP values ≥ 2.5 MoM [18] . In another report, 5 (45 % ) of
11 women with placenta accreta/percreta/increta had
second-trimester maternal serum AFP values > 2 MoMs
[40] . A third study of feasibility of Down syndrome serum
screening in an Asian population noted that women with
second-trimester maternal serum AFP ≥ 2.5 and β -hCG
MoMs were at increased risk of having placenta accreta
[OR 8.3, 95 % confidence interval (CI) 1.8 – 39.3; OR 3.9, 95 %
CI 1.5 – 9.9, respectively] [14] . Therefore, although an ele-
vated maternal serum AFP level may indicate the presence
of placenta accreta, it should not be considered as a diag-
nostic finding. Elevated AFP levels should, however, raise
suspicion and support an ultrasound-based diagnosis,
the gold standard for the prenatal detection of placenta
accreta. An important caveat about this particular risk
factor is that AFP and β -hCG levels may not be routinely
drawn in the second trimester, unless prenatal screening
is available and desired by the patient.
Although traditional ultrasound has been the most
widely used tool for diagnosis, other diagnostic modalities
exist that may aid in diagnosis in certain specific cases.
The sensitivity and specificity of ultrasound for detection
of placenta accreta are reported to be between 77 % and
90 % and between 71 % and 98 % , respectively [35] . The use
of three-dimensional (3D) ultrasound in the presence of
one 3D power Doppler criterion has been associated with
a sensitivity and specificity of 100 % and 85 % , respectively
[30] . Finally, although its use is limited by the contrain-
dication to gadolinium in pregnancy, MR imaging can be
useful in cases where there is suspicion of a posterior pla-
centa accreta, as well as in cases where the depth of inva-
sion is equivocal [20] .
Nevertheless, it is important to keep in mind that the
misdiagnosis of placenta accreta exists – only approxi-
mately 65 % of cases diagnosed as accreta with ultrasound
are actually confirmed at the time of surgery and patho-
logic examination [26] . Although no single diagnostic
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Balayla and Davis Bondarenko, Placenta accreta and the risk of adverse maternal and neonatal outcomes
7
modality determines the prenatal diagnosis of placenta
accreta with absolute accuracy, a diagnosis can be reason-
ably excluded when imaging studies suggest normal pla-
cental implantation, even in the presence of risk factors.
Additional reported risk factors for placenta accreta
include advanced maternal age and multiparity, previous
accreta, other previous uterine surgery, previous uterine
curettage, uterine irradiation, endometrial ablation, Ash-
erman syndrome, uterine leiomyomas, hypertensive disor-
ders of pregnancy, and smoking [3] . Their effect appears to
be small, and their actual contribution to the frequency of
placenta accreta remains unknown [3] . Further studies are
warranted to establish the strength of these associations.
Maternal outcomes
When antenatal detection is missed, the most imminent
and evident hint at diagnosis is profuse postpartum hem-
orrhage and placental retention after the second stage
of labor is completed. The bleeding stems from exposed
placental tissue, which remains in direct contact with the
maternal circulation. Bleeding is profuse in part due to
uterine artery blood flow, which increases substantially
by as much as 50-fold during pregnancy, to provide suf-
ficient nutrient and oxygen supply for the growth and
healthy function of the developing placenta and fetus
[24] . Poorly controlled hemorrhage is the indication for
one to two thirds of peripartum hysterectomies [13, 39] .
Antenatal diagnosis is critical as well, as preoperative
identification with scheduled cesarean hysterectomy
without placental removal is associated with significantly
reduced morbidity – 36 % vs. 67 % – compared with those
of attempted manual placental removal [9] . Maternal mor-
tality in placenta accreta remains rare. This is a reflection
of increasing antenatal detection and planned delivery.
We theorize that further elucidating the risk factors may
help increase prenatal detection and further decrease
maternal morbidity and mortality. Indeed, prenatal diag-
nosis appears to improve outcomes. In two retrospective
series, women with predelivery diagnosis of placenta
accreta had significantly lower blood loss and transfu-
sion requirements than women in whom the accreta was
diagnosed during delivery [33, 36] . What is more, mater-
nal outcomes are said to differ between surgical and con-
servative management of placenta accreta. Our review
suggests that surgical management via cesarean hyster-
ectomy should be considered as the gold standard, as is
recommended by the American College of Obstetricians
and Gynecologists [1] . Conservative/expectant manage-
ment should only be considered in centers with adequate
equipment and resources in very specific cases where fer-
tility preservation is desired [28] . Still, recommendations
for the management of placenta accreta are based on case
series and reports, personal experience, and good clini-
cal judgment. Recommendations from different societies
describe similar surgical approaches in cases of placenta
accreta. First, it is critical to develop a preoperative plan
for managing women with a high likelihood of placenta
accreta. The goal is to provide informed consent and plan
interventions that will reduce the risk of massive hemor-
rhage, as well as its substantial morbidity and potential
mortality. As mentioned above, cesarean hysterectomy
is the gold standard because if the placenta is left in situ ,
subinvolution often results in postpartum hemorrhage
and places the patient at greater risk of infection. The
delivery planning and management of placenta accreta
should be comprehensive and should ideally involve a
maternal-fetal medicine specialist in a tertiary care center
with all of the necessary resources to manage a potentially
unstable surgical patient should bleeding be profuse. Pre-
operative placement of balloon catheters into the internal
iliac arteries has also been recommended. The catheters
may be inflated intermittently during hysterectomy, thus
potentially decreasing blood loss and providing optimum
exposure of the operative field. They may also be used for
arterial embolization in those patients that have persis-
tent and important blood loss. The use of catheters has
been associated to less blood loss, lower blood transfu-
sion requirements, and shorter duration of surgery [8] .
Neonatal outcomes
Many neonatal outcomes are elucidated in this review
(Table 3). The issue of preterm delivery is an interesting
one. There are implications when considering indicated
preterm delivery in women with placenta accreta because
it is very unlikely that such patients progress beyond 36
weeks of gestation without bleeding, which may in turn
increase maternal and neonatal morbidity [3] . Such is the
risk/benefit analysis obstetric care providers must face
when approaching term. Indeed, one study reported a 44 %
(4/9) rate of emergency delivery at 36 weeks for maternal
hemorrhage in women with accreta/percreta who were
scheduled for planned cesarean-hysterectomy at a later
date [36] . In their case-control study, they retrospec-
tively analyzed data from 99 cases of placenta accreta –
62 diagnosed before delivery and 37 diagnosed intra-
partum. Planned delivery at 34 – 35 weeks after prenatal
steroids resulted in less blood use and blood loss in the
cases. Babies born to women with a prenatal diagnosis
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Balayla and Davis Bondarenko, Placenta accreta and the risk of adverse maternal and neonatal outcomes
had higher rates of steroid administration (65 % vs. 16 % ,
P < 0.001) and neonatal ICU admission (86 % vs. 60 % ,
P = 0.005), as well as longer hospital stays (10.7 vs. 6.9
days, P = 0.006). Although the length of NICU stay, rates of
respiratory distress syndrome, and surfactant administra-
tion did not differ between the planned delivery and the
unplanned groups, this reasoning makes it likely that the
neonatal outcomes are a direct consequence of iatrogenic
action leading to preterm birth, most probably second-
ary to maternal factors. From these findings, we extrapo-
late that placenta accreta may not have a direct effect of
neonatal outcomes, and therefore, an increased level of
antenatal fetal surveillance is not necessary unless it is
otherwise clinically indicated. The optimum gestational
age for scheduled delivery is controversial. Some experts
have recommended delivery of placenta accreta at 34 to 35
weeks of gestation [3, 26] . This is supported by reported
outcomes as well as a decision analysis [26, 36] .
Strengths and limitations
On the one hand, our study had several limitations. As
with all literature reviews, we had no way to validate
reported diagnoses and outcomes in the studies pub-
lished. Although some of the measures of each study
were objective, binary, and concrete (e.g., history of
cesarean vs. not, placenta previa vs. not) some of the
measured outcomes (e.g., hemorrhage, Apgar score) may
have been subject to differences in evaluation, especially
in the context of known discrepancies among interna-
tional studies and populations. Perhaps more striking,
the biggest limitation of this review was the wide hetero-
geneity in the methodology used in each reported study.
Although we were able to select those having used similar
statistical measures for the studies reporting on risk
factors, the wide differences in methodologies among
studies reporting outcomes, in addition to the lack of
access to original data, make the precise comparison
more cumbersome. Nevertheless, despite the paucity of
studies, a trend among findings is evidenced and can be
used to draw consistent conclusions.
On the other hand, this study has notable strengths.
First, to our knowledge, this is the first and only study to
compile all of the current evidence with regard to mater-
nal and neonatal outcomes in cases of placenta accreta.
This review provides an unprecedented number of cases
of placenta accreta for comparison and risk determina-
tion. Furthermore, with the increasing incidence of pla-
centa accreta, this review is a comprehensive and impor-
tant resource that addresses many aspects of an important
pathology whose rising incidence undoubtedly requires
medical awareness and expertise. Finally, the data used
are population-based and the information collected is
unlikely biased with respect to our study question.
Conclusion
Despite a paucity of trial evidence, placenta accreta
appears to be associated with adverse maternal and neo-
natal outcomes, some of which may be life threatening.
Prenatal diagnosis and adequate predelivery planning,
particularly in high-risk populations, may be indicated for
the reduction of these adverse outcomes.
Received September 10, 2012; accepted November 16, 2012
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The authors stated that there are no conflicts of interest regarding
the publication of this article.
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