Introduction
•
Managing twins
with ultrasound
Ultrasound plays an important role
in the management of twin
pregnancies.
Ana Monteagudo, MD
Outline
•
•
•
•
Assessing chorionicity & amnionicity
Establishing gestational age
Confirming viability
R/o congenital anomalies
– Management of
complications/anomalies unique to
multifetal pregnancies.
• Antenatal surveillance
Essential Embryology
• The major difference between the
dizygotic and monozygotic twins
involves the placenta.
• All dizygotic twins have
– dichorionic placentas
Chorionicity & Amnionicity
Spontaneous
Twins
• ~80% are
dizygotic and
20% are
monozygotic.
After ART
• Most twins
are dizygotic
• Increased
rate of
monozygotic
twin (~ 2.5 x)
Dizygotic
Dichorionic
(100%)
• But monozygotic twins may have
either
– dichorionic or monochorionic
placentas.
Diamniotic
(100%)
1
4 to 6 weeks
6 to 7 weeks
• Count
gestational or
chorionic sacs
• Count the
embryos in
the sacs
Number of
embryos
=
Fetal number
Number Chorionic
sacs
=
Chorionicity
1 sac
6 to 7 weeks
11 weeks
• Count the
number of
yolk sacs
Number yolk
sacs
=
number of
amnions
12 weeks
DiDi Twins 11 wks
2
Monozygotic Twins
1/3
Dichorionic
Diamniotic
(~ 99%)
4 to 7 weeks
Monochorionic Twins
Placentation
2/3
Monochorionic
Monoamniotic
(~ 1%)
Monochorionic-Diamniotic
• Single sac
with two
embryos in
the sac
Number of Yolk Sacs
Can Predict Diamniotic Twins
»Benirschke K. NY St J Med 1961;61:1499
4 to 7 weeks
• Single sac
with 2
embryos
and 2 yolk
sacs
8 weeks
...“the sonographic identification
of two yolk sacs in
monochorionic twins enables us
to make the diagnosis of
diamniotic twins early in the
first trimester, before the
amniotic membrane can be
imaged”
Bromley B and Benacerraf BR . J Ultrasound Med. 1995 Jun;14(6):415-9
3
Monochorionic-Diamniotic
9 weeks
8 weeks
Monochorionic-Monoamniotic
11 weeks
• Single sac with 2 embryos and
one yolk sac
11 weeks
Monochorionic-Monoamiotic
4
Are all twins that have a
single placental mass
monochorionic?
Of Course NOT!!
• Correct 65 out 67 cases or 97%
Twin Peak Sign vs. T-Sign
Twin Peak Sign vs. T-Sign
• In MoDi
pregnancies a
single placental
mass is seen
• In dichorionic
fused placentas
– placental tissue
may extend into
the base of the
intertwin
membrane
– the thin amniotic
membranes are
seen apposing each
other
• Seen easily
during the 1st
trimester
• Seen easily during
the 1st trimester
Diagnosis of Chorionicity &
Amnionicity
Second Trimester
100%
• 70 patients with histologic correlation
5
2nd and 3rd trimesters ultrasonographic
evaluation chorionicity & amnionicity
Opposite
Sex
“λ”
Diamniotic
Sexing
Membrane
Origin
Placental
Site
Separate
Separate
>> 2mm
2mm
4
Same
Sex
Membrane
Thickness
Membrane
layers (#)
Versus
“T”
Versus
Versus
Monoamniotic
Diamniotic
<< 2mm
2mm
2
Monochorionic
Monteagudo
Monteagudo A,
A, Timor-Tritsch
Timor-Tritsch IE..
IE.. JJ Reprod
Reprod Med
Med 2000;45:476-80.
2000;45:476-80.
See it less
well since
here the
membrane
is parallel to
the US beam
Axial resolution: the minimum reflector
separation along the sound beam, so
separate reflections are produced (In
simple terms: two point discrimination)
Fused
Fused
No
No Membrane
Membrane
Dichorionic
Axial and lateral resolution
Why don’t you
see the
membrane
uniformly well
over it’s entire
length?
See it BETTER since
here the membrane is
at a RIGHT ANGLE to
the US beam
Axial and lateral resolution
• Both can be increased by
increasing the frequency (among
others)
• The axial resolution of transducers
is always better than the lateral
resolution
Lateral resolution: The minimum reflector
separation in the direction perpendicular
to the sound beam producing separate
reflections when the sound beam scans
across them
The membranes: Di/Di twins
Ch Am
1
Horizontal
orientation of
membranes
Ch Am
Single Twin Death
• In the first trimester
– ‘Vanishing twin’ may occur in 5-10% of
twins
– In IVF associated with LBW and SGA
• Single twin demise after 1st trimester
– Less common
– The odds of IUFD and neurological
impairment is higher in monochorionic vs.
dichorionic twins
6
IVF Pregnancies
Vanishing Twin & SGA
Fetal Loss
• Monochorionic twins have higher loss
rates than dichorionic twins.
Dichorionic
Monochorionic
At least one fetal loss
< 24 wks > 24 wks
2.50%
2.80%
12.70%
4.90%
Sebire NJ et al BJOG 1997;104:1203
IVF Pregnancies
Vanishing Twin & SGA & LBW
• ~6% of all singleton deliveries after
IVF/ICSI originated from a vanishing
twin pregnancy
• A higher risk for LBW and being SGA
for survivors
• The survivors vs. control:
– LBW 26.1% vs. 12.0%
– SGA 32.6% vs. 16.3%
• In 10% of live born IVF singletons
• IVF singletons from vanishing twin
gestations have a higher risk of being
SGA than singletons from a single
gestation.
• The higher the gestational age ( > 22
wks) at the time of vanishing, the
higher the risk that the surviving infant
is being SGA.
Pinborg A et al Vanishing twins: a predictor of small-for-gestational age
in IVF singletons. Human Reproduction Vol.22, No.10 pp. 2707–2714, 2007
Prognosis for the co-twin
following single-twin death
• Systematic review - 28 articles
• The risk of greater for monochorionic vs.
dichorionic co-twin
Demise
Dichorionic
12%
4%
18%
1%
68%
57%
(95% CI 7–
7–11)
Neurological
abnormality
Preterm
delivery
Shebl O et al. Birth weight is lower for survivors of the vanishing
twin syndrome: a case-control study. Fertil Steril 2008;90:310–4.
Monochorionic
(95% CI 2–
2–7)
(95% CI 11–
11–26)
(95% CI 0–
0–7)
(95% CI 56–
56–78)
(95% CI 34–
34–77)
Ong SSC et al. Prognosis for the co-twin following single-twin
death: a systematic review.BJOG 2006;113:992–998.
Placentation and Mortality
Monochorionic Twins
Distribution of placentation
Di = 62% Mo = 38%
Mortality with placentation
Mo = 76%
2%
• Higher antenatal complications
and mortality vs. dichorionic twins
Di = 24%
11%
27%
36%
13%
44%
32%
35%
Di Di fused
Di Di separate
Mo Di
Mo Mo
From Benirschke K Ultrasound and Multifetal Pregnancy, 1998
7
Perinatal Mortality
• In monochorionic twins PM is
~ 3-4 x higher than in
dichorionic twins
Derom R et al. Eur J Obstet Gynecol
1991;41:25
» Machin G et al Am J Genet 1995;
55:71
• Risk of in utero death for Mo/Di
twins is 4X than for Di/Di.
Preterm Delivery
24 - 32 weeks
• Singleton pregnancy: 1-2%
• Twins*
– Monochorionic:9.2%
Monochorionic:9.2%
– Dichorionic:
5.5%
14.7%
• Median gestational age at
delivery*
• Even among “apparently normal twins” in utero
survival was lower for Mo/Di vs. Di/Di
– Monochorionic: 36 weeks
– Dichorionic: 37 weeks
*Sebire NJ et al BJOG 1997;104:1203
Growth Restriction
• Twins
– Risk of delivering growth
restricted baby is ~ 10X greater
than in singletons*.
• Chorionicity**
Mo
Di
One Fetus
Monochorionic 34%
Dichorionic
23%
Both
7.50%
1.70%
*Luke B, Keith LG. J Reprod Med 1992;37:661
**Sebire NJ et al BJOG 1997;104:1203
8
Selective Intrauterine Growth
Restriction (sIUGR)
Selective Intrauterine Growth
Restriction (sIUGR)
• Definition: One twin’s EFW is less
than 10th or 5th percentile for the
gestational age while the other has
normal growth.
• Associated with increased risk of
fetal death for one or both twins
• Reported to occur in 12-25% of all
MC twins
• Incidence of structural heart defects in
the general population is 8:1000
• In MC twins the incidence is increased
– Overall risk 9.1%
– MC/DA 7%
– MC/MA 57.1%
• Selective IUGR and monochorionicity
increases the risk of fetal loss
• Conclusions: The increased rate of CHD
is independent of TTS
Twin-Twin Transfusion
Syndrome
• Systematic literature review
– 9-fold increase in CHD
– If complicated by TTS 13 to 14-fold
increase compared to the general pop.
– Most common: VSD & pulmonary stenosis
• ?? Fetal echocardiography for all MC/DA
• Complicates ~15% of monochorionic
twins
• There are multiple theories on the
pathogenesis of this syndrome.
• Regardless of the pathogenesis
untreated TTS (before 28 wks) carries
a mortality rate of ~ 80% for one or
both twins*.
*Fisk NM, Taylor MJO. The fetus(s) with twin twin transfusion syndrome. In:
Harrison M et al, eds. The unborn patient. WB Saunders Co, 2000:341-55
9
Mono-Di 14 wks
Nuchal Translucency
Early Prediction of Severe
Twin-Twin Transfusion
Syndrome
• In 287 monochorionic
• In 132
twins the likelihood
monochorionic
ratio of increased NT
twins at 10 – 14
at 10-14 wks for the
wks increased NT
subsequent
in one or both
development of severe
fetuses results in
TTS was 3.5.
a 4x increased
risk of TTS
Sebire NJ et al UOG 1997;10:86
Sebire NJ et al UOG 2000;15:2008
Outcomes of TTTS Treatment
(observational studies)
• Expectant management
– Survival rate of 20% to 30%
– Neurological morbidity of 25%
• Laser coagulation vs. amnioreduction
• Serial amnioreduction
– Survival rates of 37% to 60%
– Neurological morbidity between 17-33%
– Less overall death (48% vs. 59%)
– Survival rates of 55-73%
– Neurological morbidity of 4.2%
– At 6 months more babies alive without
neurological abnormality ( 52% vs. 31%)
• Laser photocoagulation
• Septostomy
• Less perinatal death (26% vs. 44%)
• Less neonatal death (8% vs.26%)
• Amnioreduction vs. septostomy
– Survival rates up to 83%
– Neurological morbidity: no data
– No difference in perinatal outcomes
Roberts D et al. Interventions for twin-twin transfusion syndrome: a Cochrane review.
UOG 2008:31:701-711
Mono/Mono twins
Cord Entanglement
• Present from the first trimester.
• In 42 to 80% of the cases
Cord entanglement at 9 weeks 4 days
???
Color enhancement
9 wks
10
Cord
Entanglement
EGA =154/7 wks
Cord Entanglement
‘Galloping FHRs’
FHRs’
Cord Entanglement 25
6/7
wks
Malformations
• Prevalence of structural defects
per fetus in dizygotic twins is
the same as in singletons.
• In monozygotic twins rate is 23 x higher
• Concordance is uncommon
– ~ 10% in dichorionic
– ~ 20% in monochorionic
pregnancies
Burn J. Ciba Found Symp 1991;162:282
Baldwin VJ . Pathology of Multiple Pregnancy
NY: Springer Verlag: 1994;169
Conjoined Twins
Conjoined Twins 106/7 wks
11
Hearts
Livers
Bladders
Cephalothoracopagus syncephalus
Twin Reversed Arterial Perfusion
Sequence
(TRAP) “Acardiac Twin”
• Absence of
TRAP Sequence
cardiac pulsations
• Poor definition of
the head, trunk,
and upper
extremities
• Marked tissue
edema
• Deformed lower
extremities
• Two vessel cords
• Hydramnios of the
acardiac fetus
TRAP Sequence
TRAP Sequence
12
TRAP: Color Doppler Findings
TRAP
• 40 y o G1 presented for NT screen of an IVF twin
gestation at US: Mono-Di twins 11 4/7 w
• B: Acephalic, had cystic hygroma, no heart & 1 UA
• A: NL (NT of 0.7mm)
• A-to-A anastomosis
• Reversed arterial flow was confirmed
3D Surface Rendering at 14 Weeks
This modality provided
additional sonographic
evidence of TRAP sequence,
further enhancing the extent
of the malformations
3D multiplanar & surface rendering
modes
• Detection of deformed lower
limbs and rudimentary upper limb
that were barely visible
on 2D ultrasound
Mono/Mono twins
Discordant for
Anencephaly
Twin A
Antenatal Surveillance
• Dichorionic Diamniotic
– Serial growth scans q 4 weeks
– Antenatal testing starting at
• Monochorionic Diamniotic
– Serial growths scans q 4 weeks
– If discordance q 2 weeks
– Antenatal testing from 32 weeks
Entangled
Cords
Twin B
13
In Summary….
• Dizygotic Twins
– All are Dichorionic-Diamniotic (DiDi)
• Monozygotic Twins
– 1/3 are Dichorionic-Diamniotic
– 2/3 are Monochorionic-Diamniotic
• ~1% are Monochorionic-Monoamniotic
Conclusion
• Routine ultrasound is an essential
component of prenatal care for twin
gestations.
• It plays an important role in
assessing not only amnionicity and
chorionicity, but in diagnosing
abnormalities, as well as providing
fetal surveillance throughout the
duration of gestation.
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