2 Journal of Prenatal Medicine 2007; 1 (1): 2-13
Yasmine Derbala, MDFrantisek Grochal, MDPhilippe Jeanty, MD, PhD
All authors from “TheFetus.net” and “Inner Vision Women’sUltrasound”, Nashville, TN
Synonyms
Vasa praevia.
Definition
Fetal vessels crossing or running in close proximity tothe inner cervical os. These vessels course within themembranes (unsupported by the umbilical cord or pla-cental tissue) and are at risk of rupture when the sup-porting membranes rupture.
Etymology
“Vasa” is the plural of “Vas” which comes from Latinword denoting a vessel or a dish (thus the word “vase”).“Previa” is a combination of two words: “pre” (or “prae”)meaning before, and “via” meaning way. “Previa” inmedicine, usually refers to anything obstructing the pas-sage in childbirth. Literally therefore, vasa previa means“vessels in the way, before the baby”.
History
Lobstein reported the first case of rupture of vasa previain 1801 (1). Before ultrasound became common prac-tice, the diagnosis of vasa previa was often made (toolate) on the triad of ruptured membranes, painless vagi-nal bleeding (fetal bleeding: Benckiser’s hemorrhage)and fetal distress (or demise). The first ultrasound de-scription of vasa previa dates back to 1987 (2).
Prevalence
The largest studies report a prevalence of 1.5-4:10,000(3, 23). Older numbers are based on less reliable dataand should probably be abandoned. About 10% ofvasa previa occur in twins (8). Yet even in careful stud-ies, the diagnosis of vasa previa is easy to miss, evenpostnatally and thus be underreported. Thus it is likelythat the condition is not as uncommon as generallythought.
Pathogenesis
The 2 main causes of vasa previa are velamentous inser-tions (where the cord inserts directly into the membranes,leaving unprotected vessels running to the placenta) (25-62%) and vessels crossing between lobes of the placen-ta such as in succenturiate or bilobate placentas (33-75%) (36, 56). Less commonly, a vessel that courses overthe edge of a marginal placenta or a placenta previa maybecome a vasa previa after extension of the placenta overbetter vascularized area (trophotropism) (4) and involu-tion of the cotyledons that were previa (5, 6).
Vasa previa
Figure 2 - Drawing showing the inner view to the uterus, to-wards the cervix, demonstrating the anatomical relations incase of velamentous insertion of the umbilical cord.
Figure 1 - Drawing showing the inner view to the uterus, to-wards the cervix, demonstrating the anatomical relations incase of succenturiate placenta. The vessels between the mainand succenturiate lobe are crossing the inner cervical os.
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Vasa previa
Journal of Prenatal Medicine 2007; 1 (1): 2-13 3
Risk factors
Conditions associated with vessels that run close to thecervix, such as low-lying placenta (7, 8), placenta previa(9), multiple pregnancies (10), and of course multi-lo-bate placentas and velamentous insertion [1% of single-ton pregnancy (38), 10% in multifetal pregnancies (11-13)]. About 2% of velamentous insertions are associat-ed with a vasa previa (14-16).Placenta membranacea (22) is also a risk factor. It isless clear why, but in-vitro fertilization increases the riskof vasa previa (17-20), (about 1:300 pregnancies) (21).Many of these conditions present with vaginal bleedingwhich should be considered a possible alert symptomfor vasa previa.
Sonographic findings
Although vasa previa can be recognized in grey-scaleas linear structures in front of the inner os (22, 23), thediagnosis is considerably simpler by putting a flash ofcolor Doppler (color or power) (24, 25), over the cervix.Arterial flow but also venous flow can be recognized. Al-though some have obtained the diagnosis by perinealscan (26), a transvaginal image is clearly superior to anabdominal scan. Some have also advocated the use of3D (27, 59). Our impression is that 3D does not con-tribute much either in the diagnosis nor the mapping ofthe vessels since this is quite straightforward from 2Dalone. Since 3D is not universally available, its unavail-ability should not be construed as a reason to not seekvasa previa. Nevertheless, 3D allows review of the vol-ume if an unexpected finding is found at delivery. Anoth-er recent idea is to attempt to diagnose the cord inser-tion in the first trimester during the nuchal lucencyscreening, at a time when the fetus is less likely to ob-scure the cord insertion (28).
Other diagnostic procedures
Alternative methods of diagnosis such as digital palpa-tion of a vasa previa, amnioscopy, Apt, Ogita (29) orsimilar (30) tests (fetal blood detection), and palpationhave mostly a historical significance. MRI has been sug-gested too (31, 32). All these methods require a greaterexpertise then color Doppler thus cannot compare inspeed and availability.
Implications for targeted examinations
In all pregnancies, we recommend sonographic exami-nation for the placental cord insertion. In cases where the cord insertion is central and thereis no succenturiate lobe, the likelihood of a vasa previais negligible. Only those cases where the placenta islow-lying should be examined more carefully. In prac-
Figure 3 - Drawing showing the inner view to the uterus, to-wards the cervix, demonstrating the anatomical relations incase of marginal placenta with vessels running at the edge ofplacenta and crossing the inner cervical os. By trophotropism,the marginal edge of the placenta regresses, leaving the vesselin front of the inner cervical os.
Figure 4 - Pathological specimen shows the fetal side of bilo-bate placenta with velamentous insertion of the umbilical cordbetween the placental lobes. (Courtesy Francois Manson andTheFetus.net).
Figure 5 - Pathological specimen shows the maternal side ofthe bilobate placenta. (Courtesy Francois Manson and TheFe-tus.net).
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tice, a short sweep with color Doppler over the internalos will usually detect abnormal vessels over the cervix.If anything is seen in color, greater attention needs tobe paid to the region. Transvaginal (TV) sonographywith color Doppler is ideal, not only because the prox-imity of the transducer to the os and the vessels but al-so vessels that are in a coronal plane of the patient areeasier to recognize on transvaginal exam than on ab-dominal sonography. However, due to the extra timerequired and the invasiveness, this is only justifiedwhen there is a sufficient presumption on the abdomi-nal scan or risk factors (low–lying placenta, multi-lobedplacenta, multiple pregnancies, in-vitro fertilization,unidentified cord insertion, or abnormal flow over thecervix) or when there is an additional reason to do a TVscan. The following is a proposed diagnostic algorithm for thesecond-trimester detection of vasa previa (Fig. 12).During the second trimester examination (or later exam-ination if the previous information is missing), observa-tion of the placental cord insertion and the lower margin
of the placenta shows that they are both clearly far fromthe inner os. In those cases there is essentially no riskof vasa previa and no further assessment for vasa pre-via is required.Or, during the exam a succenturiate or multilobate pla-centa, velamentous insertion, a multifetal pregnancy, alow placenta, or an in-vitro fertilization is found or exists.Then an abdominal scan of cervix with color Doppler issuggested. If it is clearly normal then we go back to the“No risk” category. Or if the exam is not obviously normal, then a trans-vaginal color Doppler should be performed. If it is nor-mal, we go back to the “no or low risk” category. If thetransvaginal color Doppler is “Suspicious or abnormal”,then manage the patient as having a vasa previa. Ifduring the initial abdominal exam there is any addition-al reason for performing a transvaginal examination,perform one and if it is strictly normal, the matter canbe dropped, otherwise manage the patient as having avasa previa.This should cover most clinical situation but exceptions
Y. Derbala et al.
4 Journal of Prenatal Medicine 2007; 1 (1): 2-13
Figure 6 - Second trimester vaginal 2D sonography shows asagittal section through the cervix. In this gray scale mode novessels are visible crossing the inner cervical os.
Figure 7 - The same scan as in image 5 using color Dopplershows a vasa previa crossing the inner cervical os.
Figure 8 - Second trimester vaginal 2D sonography shows asagittal section through the cervix with the marginal placentaprevia localized at the dorsal wall of the uterus.
Figure 9 - The same scan as in image 3 using color Dopplershowing a vessel crossing the inner cervical os (vasa previa).
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are bound to happen and should be judged as theyarise.Although some studies have claimed that adding atransvaginal ultrasound to an abdominal ultrasound on-ly adds about a minute of examination time (33-35), thisdoes not include the time to explain the procedure to the
patient, obtain verbal consent, as well as patient prepa-ration. Several studies, have shown that when specificallysought, velamentous insertions and thus vasa previacan be reliably recognized (36-39), and that further, inprenatally detected vasa previa, the newborn survivalrate ranged from 97-100% in the study group. Yet, otherstudies have demonstrated that velamentous insertionsare regularly missed (40, 41).Even in skilled centers specifically attempting to iden-tify vasa previa, some cases are likely to be missed(42). In one study 1 or possibly 2 out of 11 (or 12) cas-es was missed, and false positive ranged from 10-16%(36, 37). Even when specifically sought, a predispos-ing factor such as velamentous insertion which someauthors report to recognize with 100% (39) accuracy, isonly recognized by others in 62% (43), with higher re-sult in anterior placenta (92%) and worst result in fun-dal (40%) or posterior (50%) placenta. In less skilledenvironment, the diagnosis can be missed even in thepresence of risk factors (44). Some of these studiesare getting a little old and results are improving.When a vasa previa is identified, serial scans, de-creased maternal activity and close attention to earlysigns of labor or bleeding should be recommended(36).The bottom line is that although it is unlikely that allvasa previa will be recognized, awareness of the risk
Vasa previa
Journal of Prenatal Medicine 2007; 1 (1): 2-13 5
Figure 10 - Proposed diagnostic algorithm for the second-trimester detection of the vasa previa.
Figure 11 - A second trimester vaginal 2D ultrasonographicscan shows sagittal section through the cervix with amniotic flu-id above.
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Y. Derbala et al.
6 Journal of Prenatal Medicine 2007; 1 (1): 2-13
factors and adoption of a protocol, such as the onesuggested below, to specifically seek vasa previa pluscareful examination should substantially decrease thenumber of unsuspected cases at delivery and baringtechnical problems of maternal obesity or scarring amajority (90-95%) should be recognized.
Differential diagnosis
“Linear structures” in front of the inner os in grey-scalemay also represent marginal placental sinus,chorioamniotic separation and simple folds of themembranes. The differential diagnosis of those is eas-ily established by color Doppler. Pulsed Doppler willdemonstrate a fetal umbilical or venous waveform if itis a vasa previa. Sometimes marginal placental sinusmay present with flow, but it will be a maternal heartfrequency.
Pitfalls and artifacts
Although the diagnosis of vasa previa appears straightforward, the diagnosis of cord insertion by the abdomi-nal approach is not always feasible in obese patients,those with scars or even simply difficult fetal presenta-tions. In case where the inner os is not seen on abdom-inal scans, a transvaginal examination would be recom-mended.Even on transvaginal examination there are possible pit-falls such as motion artifacts. Motion artifacts can occa-sionally give the impression on transvaginal colorDoppler of previa flow simply due to sloshing of amnioticfluid resulting from fetal motion. This artifact can be rec-ognized by its irregular nature and lack of reproducibility. Another pitfall is to confuse a funic presentation for avasa previa. These are differentiated by the shifting inposition of the cord, easily done by gently tapping withthe transducer over the region.
Figure 12 - The same second trimester vaginal sonography asin figure 2 using color Doppler showing a flushing artefact,caused by the movement of the amniotic fluid during fetal move-ment, imitating vasa previa.
Figure 15 - Second trimester vaginal Doppler image shows ahigh frequency fetal hart rate at the level of vasa previa. Thishelps to distinguish vasa previa from maternal cervical vessels.
Figure 13 - A second trimester vaginal 2D ultrasonographicscan shows sagittal section through the cervix with suspiciousvessels crossing inner cervical os (arrow).
Figure 14 - The same scan as in figure 15 using the colorDoppler clearly show that the suspicious structure is withoutDoppler signal and thus is not a vessel.
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Vasa previa
Journal of Prenatal Medicine 2007; 1 (1): 2-13 7
Tabl
e I -
Rev
iew
of s
tudi
es a
ttem
ptin
g to
iden
tify
vasa
pre
via.
Aut
hor
No.
of
Obj
ectiv
es
G.A
(wks
)M
etho
ds o
f U
mbi
lical
cor
d P
atho
gene
sis
Ass
ocia
ted
Con
clus
ions
case
sof
the
Stu
dyat
dia
gnos
isIn
vest
igat
ion
inse
rtion
of
vas
a pr
evia
com
plic
atio
nsto
iden
tify
iden
tific
atio
n
Nom
iyam
a58
7 Id
entif
y um
bilic
alM
id-
trim
este
r C
olor
Dop
pler
Spe
cific
ityV
elam
ento
us c
ord
Pre
mat
ure
rupt
ure
99.8
% (
586/
587)
et a
l. (1
998)
(555
cord
inse
rtion
scan
du
ring
rout
ine
99.8
% (
580/
581)
inse
rtion
:of
mem
bran
eof
all
cord
inse
rtion
s si
ngle
tons
,so
nogr
aphy
as
iden
tifie
d16
set
s V
elam
ento
us c
ord
18-2
0 w
ks(T
VS
*) &
(TA
S)
1 no
t see
n tu
rned
–
posi
tive
pred
ictiv
eof
twin
)in
serti
onou
t nor
mal
– va
lue
83%
(5/
6)
Vasa
pre
via
– ne
gativ
e pr
edic
tive
– va
lue
100%
(58
0/–
580)
Lee
et a
l.93
,874
Pre
nata
l ultr
a-so
und
Ave
rage
26
Abd
omin
al a
nd
Rec
ord
show
s V
elam
ento
us: 1
0 A
ntep
artu
m
Iden
tify
(200
0)di
agno
sis,
and
w
eeks
trans
vagi
nal
all c
ases
wer
ebl
eedi
ng in
6/1
8as
ympt
omat
iccl
inic
al o
ut-c
omes
w
ith D
oppl
er
iden
tifie
d B
ilobe
d pl
acen
ta: 3
(som
e w
ith fe
tal
patie
nts
befo
re
of v
asa
prev
iaE
arlie
st 1
6 ul
traso
und
intra
vent
ricul
ar
deliv
ery
wee
ksS
ucce
ntur
iate
he
mor
rhag
e)pl
acen
ta: 2
D
eliv
ery
at
Fet
al h
eart
35-3
6 w
ks a
fter
Mar
gina
l: 2
rate
abn
orm
aliti
es
mat
urity
am
nioc
ente
sis
Intra
-ute
rine
feta
l de
ath
& p
rete
rm
deliv
ery
Low
Apg
ar s
core
s
Cat
anza
rite
33,2
08S
peci
ficity
of
Mos
t at
Abd
omin
al a
nd
Vel
amen
tous
: 2S
cim
itar
synd
rom
e 10
of 1
1 ca
ses
et a
l. (2
001)
so
nogr
aphi
c20
-24
wks
trans
vagi
nal
iden
tifie
d (9
1%)
diag
nosi
s of
(67%
)ap
proa
ch
Mul
tilob
ar p
lace
nta:
8V
entri
culo
meg
aly
1 m
argi
nal p
lace
nta
vasa
pre
via
and
preg
nanc
y+
colo
r or
pow
er
Del
iver
y at
32-
37D
oppl
er
wee
ks
Sep
ulve
da
832
Iden
tifyi
ng
2nd
and
3rd
Col
or D
oppl
er
825/
832
(99%
)V
elam
ento
us: 7
/8In
fant
with
tran
sien
t82
5/83
2 (9
9%)
et a
l. (2
003)
vela
men
tous
tri
mes
ter
ultra
soun
dta
chyp
nea
cord
inse
rtion
inse
rtion
of t
he
+ (2
D)
+ (3
D)
Ecc
entri
c: 1
/8
dete
cted
cord
in r
outin
e(a
t lea
st 1
6 C
epha
loce
leob
stet
ric u
ltras
ound
wee
ks)
Tris
omy
21M
ean
= 23
wk
Res
pira
tory
dis
tress
synd
rom
e
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Y. Derbala et al.
8 Journal of Prenatal Medicine 2007; 1 (1): 2-13
Tabl
e I -
Rev
iew
of s
tudi
es a
ttem
ptin
g to
iden
tify
vasa
pre
via.
Aut
hor
No.
of
Obj
ectiv
es
G.A
(wks
)M
etho
ds o
f U
mbi
lical
cor
d P
atho
gene
sis
Ass
ocia
ted
Con
clus
ions
case
sof
the
Stu
dyat
dia
gnos
isIn
vest
igat
ion
inse
rtion
of
vas
a pr
evia
com
plic
atio
nsto
iden
tify
iden
tific
atio
n
Has
egaw
a 34
0D
etec
tion
of c
ord
9-11
wee
ksG
ray-
scal
e 31
8/34
0 (9
3.5%
)4/
283
+ 10
/35
=S
GA
= 4/
35C
ord
inse
rtion
in
et a
l. (2
006)
inse
rtion
site
trans
vagi
nal
283
norm
al c
ord
vela
men
tous
cor
d ow
er 1
/3 o
f the
(in
the
low
er th
ird
sono
grap
hyin
serti
on
inse
rtion
PR
OM
= 9
/35
lute
rus
in 1
st
of u
teru
s) d
urin
g th
e tri
mes
ter
lead
to
late
firs
t trim
este
r35
cor
d in
serti
on
4/28
3 +
5/35
=E
mer
genc
y fre
quen
t in
low
er 1
/3 o
f the
ac
cess
ory
C.S
. = 2
/35
deve
lopm
enta
lut
erus
plac
enta
ab
norm
aliti
es o
fpl
acen
ta &
cor
d.
Use
ful f
or th
e id
entif
icat
ion
of
high
-ris
k pr
egna
ncie
s
Has
egaw
a 34
46U
mbi
lical
cor
d 18
-20
wee
ksG
ray-
scal
e 33
67/ 3
421
Vel
amen
tous
25/
40
Fet
al h
eart
rate
Pre
gnan
cy w
ithet
al.
(200
6)in
serti
onul
traso
nogr
aphy
an
d 10
/336
7ab
norm
aliti
esve
lam
ento
us c
ord
and
colo
r-flo
w
40 s
uspe
cted
in
serti
on s
houl
d be
imag
ing
vela
men
tous
M
argi
nal 2
8/39
Lo
w A
pgar
hi
gh r
isk
cord
inse
rtion
and
10/3
367
scor
espr
egna
ncy
39 s
uspe
cted
M
argi
nal c
ord
inse
rtion
G.A
. =
ges
tatio
nal a
ge;
SG
A=
sm
all f
or g
esta
tiona
l age
; P
RO
M =
pre
mat
ure
rupt
ure
of m
embr
anes
;CS
= c
esar
ean
sect
ion;
TA
S =
tra
ns-a
bdom
inal
son
ogra
phy;
TV
S =
tra
ns-v
agin
al s
onog
raph
y.
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Vasa previa
Journal of Prenatal Medicine 2007; 1 (1): 2-13 9
Tabl
e II
- R
evie
w o
f re
port
ed c
ases
199
0-20
06.
Ref
eren
ce
No.
of
Vag
inal
G
.A.
(wks
)TA
S
TV
SP
atho
logy
Num
ber
ofTi
me
and
mod
e A
ssoc
iate
d an
omal
ies
case
s bl
eedi
ngat
dia
gnos
is+
+ve
ssel
sof
del
iver
y or
neo
nata
l com
plic
atio
nsas
initi
al
CD
UC
DU
pres
enta
tion
Har
ding
et
al.
1Ye
s24
wk
4d1
Suc
cent
uria
teO
ne la
rge
vess
el(1
990)
lo
be
Nel
son
et a
l.1
No
26 w
k1
Vel
amen
tous
F
our
maj
or v
esse
ls(1
990)
C
ord
inse
rtio
n
Hsi
eh e
t al
.1
No
30 w
k 1
Suc
cent
uria
teF
etal
ves
sels
(1
991)
Lo
be
Art
s et
al.
1Ye
s39
wk
1*S
ucce
ntur
iate
Sev
eral
ves
sels
39 w
k, E
lect
ive
C.S
Nor
mal
(199
3)Lo
be +
V
elam
ento
us
Cor
d in
sert
ion
Mey
er e
t al
.1
No
27 w
k1
1M
argi
nal
Larg
e ve
in a
nd
(199
3)
Cor
d in
sert
ion
smal
l art
ery
Hat
a et
al.
1Ye
s30
wk
1V
elam
ento
us
Net
wor
k of
ves
sels
(199
4)C
ord
inse
rtio
n
Fle
min
g et
al.
1N
o1
1B
ilobe
dS
ever
al v
esse
ls(1
996)
P
lace
nta
Sau
erbr
ei a
nd
1N
o36
wk
11
Vel
amen
tous
Sev
eral
ves
sels
36 w
k,E
lect
ive
C.S
.N
orm
alD
avie
s (1
998)
Cor
d in
sert
ion
1Ye
s28
wk
11
Pla
cent
a4
Ves
sels
33 w
k, E
lect
ive
C.S
.N
orm
alM
embr
anac
ea
Dev
esa
et a
l.1
No
20 w
k1
1V
elam
ento
us c
ord
Larg
e ve
ssel
37 w
k, E
lect
ive
C.S
.N
orm
al
(199
6)
inse
rtio
n
Fun
g et
al.
1Ye
s35
wk
1B
ilobe
d pl
acen
taN
etw
ork
of v
esse
ls36
wk,
Ele
ctiv
e C
.S.
Nor
mal
(199
8)
1Ye
s (h
eavy
)N
ot d
iagn
osed
1V
elam
ento
us c
ord
Net
wor
k of
ves
sels
39 w
k, E
lect
ive
C.S
.R
esus
cita
tion
+ b
lood
inse
rtio
nTr
ansf
usio
n +
con
vuls
ion
1N
oN
ot d
iagn
osed
Net
wor
k of
ves
sels
39 w
k, E
mer
genc
y C
.S.
Vel
amen
tous
cor
dN
orm
alin
sert
ion
37 w
k,E
lect
ive
C.S
.
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© CIC EDIZIONI INTERNAZIONALI
Y. Derbala et al.
10 Journal of Prenatal Medicine 2007; 1 (1): 2-13
Tabl
e II
- R
evie
w o
f re
port
ed c
ases
199
0-20
06.
Ref
eren
ce
No.
of
Vag
inal
G
.A.
(wks
)TA
S
TV
SP
atho
logy
Num
ber
ofTi
me
and
mod
e A
ssoc
iate
d an
omal
ies
case
s bl
eedi
ngat
dia
gnos
is+
+ve
ssel
sof
del
iver
y or
neo
nata
l com
plic
atio
nsas
initi
al
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pres
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tion
Oye
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wk
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elam
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ord
Net
wor
k of
ves
sels
38 w
k, N
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tillb
orn
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998)
in
sert
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Vag
inal
Del
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tus
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23
wk
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Net
wor
k of
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24 w
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mer
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ays
of li
fe1
34 w
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esse
ls (
A&
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(cho
rio-a
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psis
and
pre
mat
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Vel
amen
tous
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din
sert
ion
36 w
k, E
lect
ive
C.S
.N
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et a
l.1
No
21 w
k 1d
1(3D
)B
ilobe
d La
rge
vess
el33
wk,
Ele
ctiv
e C
.S.
Nor
mal
(200
0)M
ultip
lana
r P
lace
nta
+1
No
34 w
k 3d
volu
me
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elam
ento
us c
ord
Larg
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ssel
35 w
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ive
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orm
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light
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th
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amen
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cor
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terin
o 1
No
19 w
k1(
3D)
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ento
us c
ord
Net
wor
k of
ves
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35 w
k, E
lect
ive
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espi
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ry d
istr
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l. (2
004)
in
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Syn
drom
e
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fford
1
Yes
28w
k3
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bed
Net
wor
k of
ves
sels
30
wk
2d,
elec
tive
C.S
.N
orm
al
et a
l (20
04)
Pla
cent
a (lo
w-ly
ing
)
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lese
1
No
30 w
k1
1 +
3DB
ilobe
d pl
acen
taLa
rge
vess
el35
wk,
ele
ctiv
e C
.S.
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mal
et a
l. (2
004)
1
Yes
24 w
k1
(3D
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+3D
Vel
amen
tous
cor
dN
etw
ork
of v
esse
ls34
wk,
ele
ctiv
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.S.
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mal
inse
rtio
n
Hsi
eh1
Yes
27 w
k1
(3D
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elam
ento
us c
ord
Net
wor
k of
ves
sels
34 w
k, e
lect
ive
C.S
.N
orm
alet
al.
(200
6)
inse
rtio
n1
Yes
35 w
k1
(3D
)N
etw
ork
of v
esse
ls35
wk
2d,
elec
tive
C.S
.N
orm
alS
ucce
ntur
iate
lobe
Ush
akov
1
15 w
k1
Vel
amen
tous
cor
dF
etal
ves
sels
(in
all
Ele
ctiv
e C
.S.w
as d
one
et a
l. (2
006)
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ion
4 ca
ses)
as
a to
all
the
case
s1
22 w
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ork
of v
esse
ls(A
ll 4
case
s)1
26 w
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130
wk
1
G.A
. = g
esta
tiona
l age
; SG
A=
sm
all f
or g
esta
tiona
l age
; PR
OM
= p
rem
atur
e ru
ptur
e of
mem
bran
es;C
S =
ces
area
n se
ctio
n; T
AS
= tr
ans-
abdo
min
al s
onog
raph
y; T
VS
= tr
ans-
vagi
nal s
onog
raph
y; C
DU
= C
olor
-D
oppl
er u
ltras
onog
raph
y.
FOR REVIEW ONLY
© CIC EDIZIONI INTERNAZIONALI
Vasa previa
Journal of Prenatal Medicine 2007; 1 (1): 2-13 11
Finally, a vessel seen during a first trimester transvagi-nal scan should not be assumed to represent a vasaprevia. Too often the vessel will be of maternal originand be confused because of lateral resolution issues.Pulse Doppler will demonstrate a maternal pulse. Thediagnosis of vasa previa is thus best made in the 2nd to3rd trimester. Should a suspicious vessel be found in thefirst trimester, a repeat scan in the second trimester issuggested.
Review of the literature is provided in Tables I and II. Since vasa previa have been considered difficult to diag-nose, have not specifically been sought and are notcommon, there are unfortunately no large prospectivestudies of the condition, and the evidence about thebenefit of antenatal diagnosis relies on many small se-ries or case report.
Associated anomalies
The various reported associated anomalies are proba-bly coincidental and include cephalocele (38), Scimitarsyndrome (36) and Trisomy 21 (38). A few others can berelated to compression or damage of the vessels by thepresenting parts and includes heart rate anomalies (43),small for gestational age, and intra-ventricular hemor-rhage in a twin or even intra-uterine fetal death (23).
Prognosis
The major complication from vasa previa is the ruptureof the vessels carrying fetal blood. This occurs at or neardelivery if the condition is undetected. These results in aperinatal mortality of 56% (56) in undiagnosed cases,and 3% in those diagnosed prenatally (56). The medianApgar score (1 and 5 min) is 8 and 9 when detected pre-natally versus only 1 and 4 for survivors of undetectedcases (56). Further, transfusion is required in 58% ofnewborn without prenatal diagnosis, versus only 3% ofthose diagnosed prenatally (56). A less well quantifiedcomplication is the compression of the vasa previa bythe presenting part resulting in decreased flow to the fe-tus and possibly hypoxia (57). Postnatal complicationsare related to either prematurity (due to early C-sectionwith no confirmation of lung maturity) and include hya-line membrane disease, bronchopulmonary dysplasia,transient tachypnea, respiratory distress syndrome, orto partial exsanguination and complications related toanemia, hypovolemic shock (23) or complications oftransfusions (8).
Recurrence risk
No reported increased risk.
Management
The outcome is markedly improved (97% survival ver-sus 44%) when a prenatal diagnosis is followed by elec-tive C-section is performed at 35 weeks or earlier if
signs of labor or membrane rupture occurs (56). Somehave advocate hospitalization from 30-32 weeks withcorticosteroids to assist in promoting lung maturity whenthe cervix is not demonstrated to be long and closed(58). When time permits, an amniocentesis to assesslung maturity is justified (59).
Advocacy
In the UK – UKVP raising awareness (http://www.vas-apraevia.co.uk) has been very active in raising aware-ness on the issue (and their originators Daren & NatalieSamat deserve a lot of credit for their tireless work). Theauthors express their gratitude for their work and of thework of the International Vasa Previa Foundation(http://www.IVPF.org). Further, Dr. Oyelese has had thegreat kindness to review this manuscript and his manycorrections are greatly appreciated.
Conclusions
Although no large-scale prospective studies are there tosupport these conclusions, personal experiences, casereports and smaller studies all concur to demonstrate amarked improvement in outcome when a vasa previa isdetected prenatally. The obvious conclusion, untilproven otherwise, is that a substantial improvement inoutcome will depend only on prenatal detection. This im-plies a greater awareness of the condition and an effortat detecting it. The purpose of this manuscript is to helpalert those who do prenatal examination that vasa pre-via are not difficult to recognize when sought and thatthey are common enough to be worth seeking.
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Vasa previa
Journal of Prenatal Medicine 2007; 1 (1): 2-13 13
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