Articulo de Placent Previa

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Systematic Review

Prevalence of placenta praevia by world region: a systematicreview and meta-analysis

Jenny A. Cresswell, Carine Ronsmans, Clara Calvert and Veronique Filippi

London School of Hygiene & Tropical Medicine, London, UK

Abstract objectives (i) To estimate the prevalence burden of placenta praevia in each world region, and

(ii) to investigate potential sources of heterogeneity.

methods Systematic review of the literature and random-effects meta-analysis. Potential sources of

heterogeneity were investigated using meta-regression.

results The overall prevalence of placenta praevia was 5.2 per 1000 pregnancies (95% CI: 4.5

5.9). However, there was evidence of regional variation (P = 0.0001); prevalence was highest among

Asian studies (12.2 per 1000 pregnancies; 95% CI: 9.515.2) and lower among studies from Europe

(3.6 per 1000 pregnancies; 95% CI: 2.84.6), North America (2.9 per 1000 pregnancies; 95% CI:

2.33.5) and Sub-Saharan Africa (2.7 per 1000 pregnancies; 95% CI: 0.311.0). The prevalence of

major placenta praevia was 4.3 per 1000 pregnancies (95% CI: 3.35.4).

conclusion The prevalence of placenta praevia is low at around 5 per 1000 pregnancies. There is

some evidence suggestive of regional variation in its prevalence, but it is not possible to determine

from existing data whether this is due to true ethnic differences or other unknown factor(s).

keywords placenta praevia, antepartum haemorrhage, systematic review, meta-analysis, maternal

health, reproductive health

IntroductionPlacenta praevia is a potentially severe obstetric compli-

cation where the placenta lies within the lower segment

of the uterus, presenting an obstruction to the cervix and

thus to delivery. Risk factors for placenta praevia include

those that increase the likelihood of uterine scar tissue

(including higher parity, prior caesarean delivery or prior

abortion) or multiple gestations (Ananth et al.1997; Faiz

& Ananth 2003; Gurol-Urganciet al. 2011).

A previous systematic review by Faiz and Ananth

(2003) of studies published between 1966 and 2000 calcu-

lated the prevalence of placenta praevia to be 4.0 per

1000 pregnancies; both the search strategy and evidence

synthesis of this review emphasised North American liter-ature. Our study, conducted as part of a larger project

aiming to quantify the global burden of maternal haemor-

rhage (Calvertet al.2012), updates these results and puts

particular emphasis on capturing and including studies

originating outside of the USA and high-income countries.

Placenta praevia can result in life-threatening maternal

complications such as haemorrhage and shock and in

adverse infant outcomes such as prematurity, stillbirth and

neonatal death (Craneet al.1999, 2000; Baharet al.

2009). National hospital surveillance data from the USAdemonstrate a case-fatality rate of 17.3 deaths per 100 000

White women with placenta praevia and 40.7 deaths per

100 000 among Black women (Tuckeret al.2007). The

case-fatality rate in low-income settings is likely to be con-

siderably higher due to reduced antenatal screening and

lack of quality emergency obstetric care. The primary

objective of this paper was to estimate the prevalence of

placenta praevia in each world region; the secondary objec-

tive was to investigate potential sources of heterogeneity.

Methods

Data sources & search strategy

This review was part of a larger study investigating the

prevalence of maternal haemorrhage and the causes of

haemorrhage (Calvertet al.2012). The databases EM-

BASE, Medline, Popline, CAB Abstracts, African Index

Medicus, Eastern Mediterranean Region Index Medicus,

Latin American and Caribbean Center on Health Sciences

Information, and Western Pacific Region Index Medicus

712 2013 John Wiley & Sons Ltd

Tropical Medicine and International Health doi:10.1111/tmi.12100

volume 18 no 6 pp 712724 june 2013


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were searched using thesaurus and free-text terms to iden-

tify literature published from 1 January 1990 onwards.

The initial search strategy identified studies published up

until 2009; the search was later updated in April 2012.

The search strategy included thesaurus and free-textterms relating to haemorrhage, placenta praevia and

bleeding. A particular effort was made to identify litera-

ture from low-income settings by searching the WHO

regional databases. The reference lists of eligible studies

were hand searched to identify further publications. The

full search strategy is available upon request.

Inclusion criteria

Studies were eligible for inclusion if they reported the

number of cases of placenta praevia, along with a suitable

denominator for the total number of deliveries or births in

the population, and the median year of the study was1990 onwards. To capture population-representative data,

facility-based studies were excluded if local or national (if

local data unavailable) skilled birth attendance was

97%) of heterogeneity was

observed for all and major cases, which remained even

after stratification by study characteristic (Table 1). Inthe meta-regression (Table 2), the only study characteris-

tic with a significant effect on prevalence of all cases of

placenta praevia was geographic region (P = 0.0001).

Although region could explain around half of the

between-study variance, there was still a very high level

of residual heterogeneity after accounting for region

(98.5%).

Discussion

Our results show that the prevalence of placenta praevia

was around 5.2 cases per 1000 pregnancies (95%

CI: 4.5

5.9); the prevalence of major placenta praeviawas 4.3 cases per 1000 pregnancies (95% CI: 3.35.4).

Heterogeneity was very high, even after stratification on

study characteristics.

Geographic region was the only study characteristic

with a significant influence on prevalence. Prevalence was

highest among Asian studies (12.2 per 1000) and lower

among studies from Europe (3.6 per 1000), North Amer-

ica (2.9 per 1000) and Sub-Saharan Africa (2.7 per

2013 John Wiley & Sons Ltd 713

Tropical Medicine and International Health volume 18 no 6 pp 712724 june 2013

J. A. Cresswell et al. Placenta praevia by world region


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1000). This could plausibly be due to true geographic or

ethnic differences between populations; several previous

studies have found the prevalence of placenta praevia to

vary between different ethnic groups (Sheineret al. 2001;

Ananthet al. 2003), including increased prevalence

among Asian women relative to White women (Shen

et al.2005). Any biological mechanism for this associa-

tion is poorly understood; however, ethnic differences in

prematurity rates or pelvic structure are possible explana-tions. It has been observed that normal gestational length

is shorter among Black and Asian women than among

White European women (Patel et al. 2004). However, it

is also possible that the apparent importance of the geo-

graphic region variable is a marker for other (unknown)

causes of heterogeneity between the studies. The majority

of studies identified in this review did not report the

distance between the placental edge and the cervical os;

subtle differences in national diagnostic protocols or con-

ventions may account in part for the observed regional

differences.

This study has investigated the prevalence of placenta

praevia in more diverse geographic locations than previ-

ously. However, there are a number of limitations.

Despite our best efforts, we retrieved a relatively small

number of studies from low- and middle-income coun-

tries. This partially reflects an imbalance in where studieson placenta praevia are conducted; however, this was

also partially due to our a prioridecision to only include

facility-based studies where skilled birth attendance was

>95%. We acknowledge that doing so has meant that we

have very few studies from some regions, such as Sub-

Saharan Africa, and that consequently our estimates can-

not be interpreted as representative of the entire region.

Nevertheless, we believe that our strategy was preferable

Original search on haemorrhage &causes of haemorrhage to

31stDecember 20091stApril 2012

MEDLINE, Embase, PoplineMEDLINE, Embase, Popline

LILIACS, CAB, EMRIM, AIM, WPRIMLILIACS, CAB, EMRIM, AIM, WPRIM

n= 13 205

n= 5121

n= 887

n= 136

n= 785

n= 12 182

n= 102

n= 36

n= 10

n= 12

Full text obtained

n= 68Full text obtained

Full text not available

Contained potentially relevantinformation on placenta praevia

Met inclusion criteria Met inclusion criteria

Inclusion in meta-analysis n= 48

Did not contain any information

related to placenta praevia

Exclusions:Skilled birth attendance


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Table

1

Random-effectsmeta-analysisofpooledprevalenceofplacentapraevia,stratifiedbycovariates

Characteristic

No.of

Studiesk

Pooledprevalenceper1000

pregnancies

Variationdue

toStudy

Heterogeneity(I2)

n

Prevalence

(95%

CI)

Allcasesofplacentapraevia

(marginal,partialorcomplete)

GBDRegion

Asia(Hendr

icksetal.1999;Yamadaetal.2005;Fujii

etal.2010;

Huangeta

l.2011;Jangetal.2011;Matsudaetal.2

011)

6

378

856

12.2

(9.5,15.2)

97.7%

Australasia(Oliveetal.2006;Lainetal.2008;McCormacketal.2008)

3

505

82

9.5

(4.8,15.7)

95.0%

Europe(Taipaleetal.1998;DSouza2000;Vettrainoetal.2001;

Grgicetal

.2004;Loveetal.2004;Romundstadeta

l.2006;Tuzovic

2006;Papinniemietal.2007;Tataetal.2007;Milos

evicetal.2009;

VazquezRodriguezetal.2010;Daskalakisetal.2011;Rosenbergetal.

2011)

13

146

1928

3.6

(2.8,4.6)

98.1%

LatinAmeri

ca&theCaribbeanCabrera(Hernandeze

tal.1999;

Faneiteetal.2001;Rivasetal.2001)

3

400

58

5.1

(2.5,8.7)

94.4%

NorthAfrica/MiddleEast(Ismail2001;Bhatetal.200

4;Baharetal.

2009;CelikAciogluetal.2010;Davoodetal.2010;

Alshamietal.2011)

6

995

44

6.4

(5.6,7.3)

57.8%

NorthAmer

ica(Ananthetal.2001;Francoisetal.2003;Koroukian2004;

Shenetal.

2005;Predanicetal.2007;Yangetal.2009;Aliyuetal.

2011a,b;E

ichelbergeretal.2011)

8

196

88426

2.9

(2.3,3.5)

99.5%

Sub-Saharan

Africa(Prualetal.2000;Buambo-Baman

gaetal.2004)

2

405

60

2.7

(0.3,11.0)

99.2%

WorldBank

Classification

Highincome(Taipaleetal.1998;Hendricksetal.199

9;DSouza2000;

Ananthet

al.2001;Vettrainoetal.2001;Francoisetal.2003;

Bhatetal.

2004;Koroukian2004;Loveetal.2004;Shenetal.2005;

Yamadaet

al.2005;Oliveetal.2006;Tuzovic2006;Romundstadetal.

2006;Papinniemietal.2007;Predanicetal.2007;Tataetal.2007;

McCormac

ketal.2008;Baharetal.2009;Yangetal.2009;Braggetal.

2010;Fujii

etal.2010;VazquezRodriguezetal.2010;Aliyuetal.

2011a,b;A

lshamietal.2011;Daskalakisetal.2011;Eichelbergeretal.

2011;Jang

etal.2011;Matsudaetal.2011;Rosenbergetal.2011)

30

215

59572

5.2

(4.4,6.0)

99.6%

Upper-middleincome(CabreraHernandezetal.1999;

Faneiteetal.2001;

Ismail2001;Rivasetal.2001;Grgicetal.2004;Milosevicetal.2009;

CelikAciogluetal.2010;Davoodetal.2010;Huangetal.2011)

9

149

822

5.8

(3.5,8.8)

97.8%

LowandLo

wer-middleincome(Prualetal.2000;Bua

mbo-Bamangaetal.

2004)

2

405

60

2.7

(0.3,11.0)

99.2%





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Table1

(continued)

Characteristic

No.of

Studiesk


pregnancies

Variationdue

toStudy

Heterogeneity(I2)

n

Prevalence

(95%

CI)

Languageof

Publication

English(Taipaleetal.1998;Hendricksetal.1999;D

Souza2000;

Ananthet

al.2001;Ismail2001;Francoisetal.2003;Bhatetal.2004;

Koroukian

2004;Loveetal.2004;Shenetal.2005;Yamadaetal.2005;

Oliveetal

.2006;Romundstadetal.2006;Tuzovic2

006;Tataetal.

2007;Papinniemietal.2007;Predanicetal.2007;M

cCormacketal.

2008;Baharetal.2009;Yangetal.2009;Braggeta

l.2010;Davood

etal.2010

;Fujiietal.2010;Aliyuetal.2011a,b;Alshamietal.2011;

Daskalakis

etal.2011;Eichelbergeretal.2011;Huangetal.2011;

Jangetal.

2011;Matsudaetal.2011;Rosenbergetal.2011)

31

215

90322

5.5

(4.7,6.3)

99.6%

Non-English

(CabreraHernandezetal.1999;Prualet

al.2000;

Faneiteetal.2001;Rivasetal.2001;Vettrainoetal.2001;

Buambo-Bamangaetal.2004;Grgicetal.2004;Milosevicetal.2009;

CelikAciogluetal.2010;VazquezRodriguezetal.2

010)

10

159

622

4.2

(2.7,6.2)

96.5%

StudySetting

Facility-base

d(Taipaleetal.1998;CabreraHernandez

etal.1999;

Hendricks

etal.1999;DSouza2000;Faneiteetal.2

001;Ismail2001;

Rivasetal

.2001;Vettrainoetal.2001;Francoiseta

l.2003;

Bhatetal.

2004;Buambo-Bamangaetal.2004;Grgicetal.2004;

Loveetal.

2004;Yamadaetal.2005;Oliveetal.2006;Tuzovic2006;

Papinniemietal.2007;Predanicetal.2007;McCorm

acketal.2008;

Baharetal.2009;Milosevicetal.2009;CelikAciogluetal.2010;

Davoodet

al.2010;VazquezRodriguezetal.2010;Alshamietal.2011;

Daskalakis

etal.2011;Eichelbergeretal.2011;Jang

etal.2011)

28

547

893

5.2

(4.3,6.2)

95.9%

Population-based(Prualetal.2000;Ananthetal.2001;Koroukian2004;

Shenetal.

2005;Romundstadetal.2006;Tataetal.2007;

Yangetal.2009;Braggetal.2010;Fujiietal.2010;Aliyuetal.2011a,b;

Huangeta

l.2011;Matsudaetal.2011;Rosenberget

al.2011)

13

212

02060

5.0

(3.9,6.3)

99.8%





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Table1

(continued)

Characteristic

No.of

Studiesk


pregnancies

Variationdue

toStudy

Heterogeneity(I2)

n

Prevalence

(95%

CI)

Confirmation

ofPlacenta

Praevia

Diagnosis

Confirmeda

tdelivery(Taipaleetal.1998;CabreraHernandezetal.1999;

Hendricks

etal.1999;DSouza2000;Ananthetal.2

001;

Rivasetal

.2001;Francoisetal.2003;Buambo-Bamangaetal.2004;

Oliveetal

.2006;Romundstadetal.2006;Papinniem

ietal.2007;

Baharetal.2009)

13

161

7940

4.4

(3.2,5.7)

98.9%

Presentatla

stultrasoundpriortodelivery(Faneiteetal.2001;Ismail

2001;Bhatetal.2004;Loveetal.2004;Yamadaet

al.2005;

Tuzovic20

06;Predanicetal.2007;Daskalakisetal.

2011;

Eichelbergeretal.2011;Jangetal.2011;Matsudaetal.2011;

Rosenberg

etal.2011)

11

626

884

6.1

(3.7,9.1)

99.4%

Notreported(Prualetal.2000;Vettrainoetal.2001;

Grgicetal.2004;

Koroukian

2004;Shenetal.2005;Tataetal.2007;McCormacketal.

2008;Milo

sevicetal.2009;Yangetal.2009;Bragg

etal.2010;Celik

Aciogluet

al.2010;Davoodetal.2010;Fujiietal.2

010;Vazquez

Rodriguez

etal.2010;Aliyuetal.2011a,b;Alshamietal.2011;

Huangeta

l.2011)

17

195

05130

5.2

(4.3,6.2)

99.5%

Definitionof

denominator

Alldeliveries(CabreraHernandezetal.1999;Prualet

al.2000;

Faneiteetal.2001;Ismail2001;Rivasetal.2001;Vettrainoetal.2001;

Francoisetal.2003;Bhatetal.2004;Buambo-Bamangaetal.2004;

Grgicetal

.2004;Loveetal.2004;Shenetal.2005;

Yamadaetal.

2005;Oliveetal.2006;Tuzovic2006;Tataetal.20

07;Milosevicetal.

2009;Brag

getal.2010;CelikAciogluetal.2010;D

avoodetal.2010;

Rosenberg

etal.2011)

21

174

9648

4.6

(3.6,5.7)

98.5%

AllLiveBirths(Huangetal.2011)

1

212

34

17.5

(15.8,19.4)

Allsingleton

deliveries(Taipaleetal.1998;Hendricks

etal.1999;

DSouza2000;Romundstadetal.2006;Papinniemietal.2007;

Predanicetal.2007;McCormacketal.2008;Baharetal.2009;

Fujiietal.

2010;VazquezRodriguezetal.2010;Aliy

uetal.2011a,b;

Alshamiet

al.2011;Daskalakisetal.2011;Eichelbergeretal.2011;

Jangetal.

2011;Matsudaetal.2011)

16

260

7980

5.8

(4.0,8.0)

99.7%

AllSingletonLiveBirths(Ananthetal.2001;Koroukian2004;Yangetal.

2009)

3

173

71092

3.5

(2.4,4.8)

99.6%





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Table1

(continued)

Characteristic

No.of

Studiesk


pregnancies

Variationdue

toStudy

Heterogeneity(I2)

n

Prevalence

(95%

CI)

Overall

41

21749954

5.2

(4.5,5.9)

99.5%

Majorplacentapraevia(partialorcomplete)

GBDRegion

Asia(Hendr

icksetal.1999;Hungetal.2007;Sumiga

maetal.2007;

Hasegawa

etal.2009;Jangetal.2011)

5

164

559

8.0

(6.0,10.3)

95.6%

Australasia

0

Europe(Taipaleetal.1998;DSouza2000;Beckeret

al.2001;Grgicetal.

2004;Loveetal.2004;Guarigliaetal.2006;Daskalakisetal.2011)

7

127

485

3.2

(1.9,4.8)

94.9%

LatinAmerica&theCaribbeanCabrera(Hernandeze

tal.1999;Faneite

etal.2001

;Rivasetal.2001)

3

400

58

3.3

(1.3,6.1)

93.8%

NorthAfrica/MiddleEast(Bhatetal.2004;Bahareta

l.2009)

2

514

94

4.1

(3.6,4.7)

0.0%

NorthAmer

ica(Craneetal.2000;Cleary-Goldmanet

al.2005;

Predanicetal.2007;Eichelbergeretal.2011)

4

166

458

3.0

(1.5,5.0)

97.1%

Sub-Saharan

Africa(Buambo-Bamangaetal.2004)

1

202

34

5.3

(4.4,6.4)

Worldbank

classification

Highincome(Taipaleetal.1998;Hendricksetal.199

9;Craneetal.

2000;DSo

uza2000;Beckeretal.2001;Bhatetal.2

004;Loveetal.

2004;Clea

ry-Goldmanetal.2005;Guarigliaetal.2006;Predanicetal.

2007;Sumigamaetal.2007;Baharetal.2009;Hasegawaetal.2009;

Daskalakis


etal.2011)

16

463

284

4.3

(3.3,5.4)

96.3%

Upper-middleincome(CabreraHernandezetal.1999;

Faneiteetal.2001;

Rivasetal

.2001;Grgicetal.2004;Hungetal.2007

)

5

867

70

4.1

(1.1,8.7)

98.6%

LowandLo

wer-middleincome(Buambo-Bamangaet

al.2004)

1

202

34

5.3

(4.4,6.4)

Languageof

Publication

English(Taipaleetal.1998;Hendricksetal.1999;Cr

aneetal.2000;

DSouza2000;Beckeretal.2001;Bhatetal.2004;L

oveetal.2004;

Cleary-Goldmanetal.2005;Hungetal.2007;Preda

nicetal.2007;

Sumigama

etal.2007;Baharetal.2009;Hasegawaetal.2009;

Daskalakis


etal.2011)

16

473

560

4.5

(3.3,6.0)

97.7%

Non-English

(CabreraHernandezetal.1999;Faneiteetal.2001;Rivas

etal.2001

;Buambo-Bamangaetal.2004;Grgiceta

l.2004;

Guarigliae

tal.2006)

6

967

28

3.6

(2.2,5.4)

94.2%





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Table1

(continued)

Characteristic

No.of

Studiesk


pregnancies

Variationdue

toStudy

Heterogeneity(I2)

n

Prevalence

(95%

CI)

StudySetting

Facility-base

d(Taipaleetal.1998;CabreraHernandez

etal.1999;

Hendricks

etal.1999;DSouza2000;Beckeretal.2001;Faneiteetal.

2001;Riva

setal.2001;Bhatetal.2004;Buambo-Bamangaetal.2004;

Grgicetal

.2004;Loveetal.2004;Cleary-Goldman

etal.2005;

Guarigliae

tal.2006;Hungetal.2007;Predaniceta

l.2007;Sumigama

etal.2007

;Baharetal.2009;Hasegawaetal.2009;

Daskalakisetal.

2011;Eichelbergeretal.2011;Jangetal.2011)

21

476

292

4.3

(3.3,5.5)

97.1%

Population-based(Craneetal.2000)

1

939

96

3.2

(2.9,3.6)

Confirmation

ofPlacenta

Praevia

Diagnosis

Confirmeda

tdelivery(Taipaleetal.1998;CabreraHernandezetal.1999;

Hendricks

etal.1999;Craneetal.2000;DSouza20

00;

Beckereta

l.2001;Rivasetal.2001;Buambo-Baman

gaetal.2004;

Cleary-Goldmanetal.2005;Guarigliaetal.2006;Baharetal.2009)

13

366

688

4.5

(3.2,6.0)

97.4%

Presentatla

stultrasoundpriortodelivery(Faneiteet

al.2001;

Bhatetal.

2004;Loveetal.2004;Predanicetal.2007;

Sumigama

etal.2007;Hasegawaetal.2009;Daskalakisetal.2011;

Eichelbergeretal.2011;Jangetal.2011)

8

194

590

4.4

(2.6,6.4)

97.2%

Notreported(Grgicetal.2004;Hungetal.2007)

1

901

0

1.3

(0.7,2.2)

Definitionof

denominator

Alldeliverie

s(CabreraHernandezetal.1999;Cranee

tal.2000;

Beckereta

l.2001;Faneiteetal.2001;Rivasetal.2001;

Bhatetal.

2004;Buambo-Bamangaetal.2004;Grgicetal.2004;

Loveetal.

2004;Guarigliaetal.2006;Sumigamaet

al.2007;

Hasegawa

etal.2009)

12

322

601

4.1

(3.0,5.3)

95.8%

Alllivebirths

0

Allsingleton

deliveries(Taipaleetal.1998;Hendricks

etal.1999;

DSouza2000;Cleary-Goldmanetal.2005;Hungeta

l.2007;

Predanicetal.2007;Baharetal.2009;Daskalakisetal.2011;

Eichelbergeretal.2011;Jangetal.2011)

10

247

687

4.6

(2.8,6.7)

98.1%

AllSingletonLiveBirths

0

Overall

22

570288

4.3

(3.3,5.4)

97.2%





9/13

Table

2

Meta-regression

Studycharacteristic

OR

[95%

confidence

interval]

Testforc

ovariate

withKnapp-Hartung

modification

Proportion

ofbetween-study

varianceexplained

(AdjustedR2)

Residual

variation

duetostudy

heterogeneity

(ResidualI2)

Allcasesofplacentapraevia

(marginal,partialorcomplete)

GBDRegion

Asia

1.00

F

=

6.96;

P

=

0.00

01

50.4%

98.5%

Australasia

0.78

[0.361.68]

Eu

rope

0.29

[0.170.49]

La

tinAmerica&theCaribbean

0.42

[0.190.90]

NorthAfrica/MiddleEast

0.55

[0.301.03]

NorthAmerica

0.24

[0.130.42]

Su

b-SaharanAfrica

0.19

[0.080.46]

WorldBank

Classification

Highincome

1.00

F

=

1.32;

P

=

0.27

86

Upper-middleincome

1.13

[0.641.99]

Lo

wandLower-middleincome

0.44

[0.141.33]

Languageof

Publication

En

glish

1.00

F

=

0.89;

P

=

0.35

22

Non-English

0.77

[0.451.34]

StudySetting

Fa

cility-based

1.00

F

=

0.49;

P

=

0.48

89

Po

pulation-based

0.84

[0.511.39]

Confirmation

ofPlacenta

PraeviaDiagnosis

Confirmedatdelivery

1.00

F

=

0.56;

P

=

0.57

54

Pr

esentatlastultrasoundpriortodelivery

1.38

[0.742.56]

Notreported

1.11

[0.631.93]

Definitionof

Denominator

Alldeliveries

1.00

F

=

1.70;

P

=

0.18

46

Alllivebirths

4.22

[0.9618.49]

Allsingletondeliveries

1.28

[0.782.08]

Allsingletonlivebirths

0.82

[0.342.00]

Majorplacenta

praevia(partial

orcomplete)

GBDRegion

Asia

1.00

F

=

2.64;

P

=

0.05

33

30.9%

95.3%

Eu

rope

0.39

[0.210.75]

La

tinAmerica&theCaribbean

0.40

[0.180.90]

NorthAfrica/MiddleEast

0.53

[0.211.31]

NorthAmerica

0.36

[0.170.75]

Su

b-SaharanAfrica

0.67

[0.212.18]

WorldBank

Classification

Highincome

1.00

F

=

0.16;

P

=

0.85

48

Upper-middleincome

0.89

[0.441.81]

Lo

wandLower-middleincome

1.31

[0.335.19]

Languageof

Publication

En

glish

1.00

F

=

0.48;

P

=

0.49

59

Non-English

0.81

[0.431.53]





10/13

to any alternative to enhance the validity of our esti-

mates.

The true prevalence of placenta praevia is likely to lie

somewhere between that estimated by the facility-based

and population-based designs. Facility-based studies mayoverestimate prevalence because of referral patterns. Con-

versely, estimates from population-based studies may

underestimate the prevalence of placenta praevia due to

the increased potential for missing cases. Population-

based studies are more likely to lack detailed information

on the grade of the placenta praevia, and clinical diagno-

sis procedures and many population-based studies restrict

the denominator to live births, which excludes cases of

placenta praevia accompanied by stillbirth.

Placenta praevia is a rare condition and may have been

subject to differential under-reporting depending on local

antenatal routines, which are difficult to ascertain at the

aggregate level. For example, one Sub-Saharan studyPrualet al. 2000 reported a substantially lower preva-

lence (0.59 cases per 1000 pregnancies) than other studies

in this review. This study predominantly identified cases

of placenta praevia that were accompanied by a maternal

haemorrhage, and likely missed those with less serious

outcomes, which would be identified in well-resourced

settings where women may have multiple ultrasounds

during pregnancy.

We observed very high levels of heterogeneity in this

review. Most of the studies included in this review had

large sample sizes that produced very precise estimates.

Because within-study variance was very small compared

to between-study variance, high I2 values were observed.Statistically significant differences between study esti-

mates were not necessarily clinically significant.

In conclusion, the prevalence of placenta praevia is

low, but remains a serious obstetric complication with a

high case-fatality rate. There is some evidence to suggest

regional variation in the prevalence of placenta praevia,

although it is not possible to determine from studies such

as this whether this is due to true population differences

or some unknown factor.

Acknowledgements

This project was funded by a grant from the Bill andMelinda Gates Foundation to the US Fund for UNICEF to

support the Child Health Epidemiology Reference Group

(PI: Robert E Black). The authors acknowledge the valu-

able contributions of Alma Adler, Sara Thomas and Karen

Wagner to the project. The authors would like to thank

Fernanda Boueri, Kathryn Church, Xing Lin Feng, Sylvia

Marinova, Ana Montoya, Yusuke Shimakawa and Kate-

rini Storeng for their help translating articles.Table2

(continued)

Studycharacteristic

OR

[95%

confidence

interval]

Testforc

ovariate

withKnapp-Hartung

modification

Proportion

ofbetween-study

varianceexplained

(AdjustedR2)

Residual

variation

duetostudy

heterogeneity

(ResidualI2)

Confirmation

ofPlacentaPraevia

Diagnosis

Confirmedatdelivery

1.00

F

=

1.43;

P

=

0.26

30

Pr

esentatlastultrasoundpriortodelivery

0.96

[0.541.69]

Notreported

0.32

[0.081.31]

Definitionof

Denominator

Alldeliveries

1.00

F

=

0.10;

P

=

0.75

57

Allsingletondeliveries

1.09

[0.621.92]





11/13

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Supporting Information

Additional Supporting Information may be found in the

online version of this article:

Appendix S1. Description of eligible studies.

Corresponding AuthorJenny A. Cresswell, London School of Hygiene & Tropical Medicine, Keppel St, London WC1E 7HT,

UK. E-mail: [email protected]




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