Ultrasonography of twin pregnancy SOGC GUIDELINE

1. ABOUBAKR ELNASHAR
Ultrasonography of
twin pregnancy
SOGC GUIDELINE
Aboubakr Elnashar
Benha University, Egypt

2. 5. Assessment of fetal growth
6. Assessment of Fetal wellbeing
7. Assessment of amniotic fluid
8. Assessment of umbilical artery
Doppler
9. Diagnosis of rare obstetrical
complications unique to twins
10. Placental localization, and fetal
position for intrapartum
management.
1. Determination of
chorionicity &
amnionicity
2. Determination of
gestational age
3. Screening for
anomalies
4. Screening for PTL
CONTENTS
TYPES
CLINICAL USES OF ULTRASONOGRAPHY
ABOUBAKR ELNASHAR

3. TYPES
 1–2% of all pregnancies.
 Zygosity:-
2/3rd (Dizygotic) and 1/3rd (Monozygotic).
 Chorionicity:-
Dichorionic(80%):- all Dizygotic and 1/3rd of Monozygotic.
Monochorionic (20%):- 2/3rd of Monozygotic
Dizygotic Monozygotic
ABOUBAKR ELNASHAR

4. Dizygotic twin
– 2 placentas (may be fused)
Monozygotic twin
1.Dichoriotic / Diamniotic
2 placentas (may be fused)
2.Monochoriotic / Diamniotic
1 placenta
3.Monochoriotic / Monoamniotic –
1 placenta
ABOUBAKR ELNASHAR

5. 1.DETERMINATION OF CHORIONICITY AND
AMNIONICITY
Critical in the management
When?:
1st T.
Why?
1. Management of structural anomalies
2. Screening for aneuploidy,
3. Etiology of fetal growth and/or fluid discordance
4. Early diagnosis of TTT syndrome
5. Management of a surviving twin following
intrauterine demise
ABOUBAKR ELNASHAR

6. {high mortality and morbidity of monoamniotic
twins}: early and intensive monitoring and
intervention: improve outcomes
Before 10 w
sonographic findings to determine chorionicity.
Number of
1. gestational sacs
2. amniotic sacs within the chorionic cavity
3. yolk sacs.
ABOUBAKR ELNASHAR

7. 1. Number of Gestational Sacs
Each gestational sac forms its own placenta and
chorion:
2 gestational sacs: DC twin
1 gestational sac with 2 identified heartbeats: MC
twin
ABOUBAKR ELNASHAR

8. 2. Number of Amniotic Sacs Within the
Chorionic Cavity
Diamniotic twins:
±separate and distinct amnions
{before 10w the separate amnions of a diamniotic
pregnancy will not have enlarged sufficiently to
contact each other and create the inter-twin
septum}.
TAS: {Each single amnion is extremely thin and
delicate: ±very difficult to see
TVS: often successful in differentiating separate
amnions.
ABOUBAKR ELNASHAR

9. 3. Number of Yolk Sacs
2 yolk sacs are seen in the extra-embryonal
coeloma: diamniotic
 1 yolk sac
in most cases indicate monoamniotic twins
when there are dual embryos: a follow-up 1st T
scan to definitively assign amnionicity.
ABOUBAKR ELNASHAR

10. ABOUBAKR ELNASHAR

11. ABOUBAKR ELNASHAR

12. After 10 weeks
These sonographic signs are no longer present:
gestational sacs are no longer distinctly separable,
and the inter-twin membrane is formed.
Findings:
(1) Genitalia,
(2) Placental number
(3) Chorionic peak sign
(4) Membrane characteristics.
ABOUBAKR ELNASHAR

13. The following order provides a logical sequence to
determine chorionicity after 10 w.
step 1 is not routinely used at the 10-14 w
1. Sex Discordance
Phenotypic discordance: DC in all but the rarest
cases.
Concordance of phenotype does not rule out
dichorionicity.
ABOUBAKR ELNASHAR

14. 2. Number of Distinct Placentas
1 placental mass: MC
2 distinct, separate placentas: DC
Careful sonographic examination may help
distinguish a single placenta from 2 placentas in
abutment.
ABOUBAKR ELNASHAR

15. 3. Presence or Absence of the Chorionic Peak
(twin peak or lambda sign)
Projecting zone of tissue of similar echotexture to
the placenta
Triangular in cross-section and wider at the
chorionic surface of the placenta, extending into,
and tapering to a point within, the inter twin
membrane.
 Most often identifies DC
MC: absence of the twin peak sign.
ABOUBAKR ELNASHAR

16. 4. Inter-Twin Membrane Characteristics
DC :
 2 layers of amnion and 2 layers of chorion.
Thicker > 2 mm: PPV: 95%
more reflective
MC:
≤ 2mm: PPV: 90%.
In 2nd T:
Number of membranes may be counted, and if there
are > 2, then dichorionicity is strongly suggested
ABOUBAKR ELNASHAR

17. DC twin
Lambda sign
thick membrane
Absent membrane in a
monoamniotic twin.
ABOUBAKR ELNASHAR

18. Dichorionic Twins (80%)
(Two placentas)
Lambda sign
Monochorionic Twins (20%).
(One placenta)
T sign
ABOUBAKR ELNASHAR

19. ABOUBAKR ELNASHAR

20. Dichorionic Diamniotic twin: a triangular projection of
chorionic tissue emanating from fused dichorionic placentas
and extending between layers of the intertwin membrane.
ABOUBAKR ELNASHAR

21. Dichorionic twin in the first trimester: a thick inter twin
membrane
ABOUBAKR ELNASHAR

22. Monochorionic Twins
thin intertwin membrane Monochorionic Twins
(20%).
(One placenta)
T sign
ABOUBAKR ELNASHAR

23. If a membrane is not detected:
careful evaluation to diagnose or exclude
monochorionic monoamniotic twinning
Possibilities:
1. Monoamniotic twinning
2. Twin with complete oligohydramnios (stuck twin)
3. Diamniotic twin pregnancy in which the
membrane is present but not seen
{its thinness and orientation to the transducer}.
ABOUBAKR ELNASHAR

24. The most definitive sonographic finding in the
diagnosis of monoamniotic twins:
Cord entanglement from the placental or umbilical
origin
Colour Doppler may facilitate identification of this
finding.
Entanglement of limbs or observation of a limb
circumscribing the other
Failure to find the membrane between the 2 cord
insertions in the placenta
TVS: is often a helpful adjunct to TAS in identifying
the membrane.
ABOUBAKR ELNASHAR

25. ABOUBAKR ELNASHAR

26. 2. DETERMINING GESTATIONAL AGE
When:
1st T: ideal time
{statistically superior to 2nd T dating}.
How:
 1st T:
CRL: ±5d
 2nd T:
1. BPD: ± 7d
ABOUBAKR ELNASHAR

27. 2. Best estimate: combination of
HC
AC
FL.
ABOUBAKR ELNASHAR

28. When twin pregnancy is the result of IVF,
accurate determination of gestational
age should be made from the date of embryo
transfer. (II-1A)
To avoid missing a situation of early IUGR in one
twin, most experts agree that the clinician may
consider dating pregnancy using the larger fetus.
(III-C)
ABOUBAKR ELNASHAR

29. 3. SCREENING FOR ANOMALIES
1. Aneuploidy Screening in 1st T
Nuchal transluscency and maternal age.
Using the average NT:
NT in conjunction with maternal age: 75% sensitivity
Useful in the early detection or prediction of TTTS.
An NT threshold at the 95th percentile had a
PPV:43%
NPV: 91%
ABOUBAKR ELNASHAR

30. 2. Aneuploidy Screening in the 2nd T
Soft markers of Down syndrome
Nonossified nasal bone
linear arrangement of the tricuspid and mitral valves within
the heart
thickened nuchal skin fold
slightly short humerus relative to head size
slightly short femur relative to head size
echogenic intracardiac focus
fetal hydronephrosis
ABOUBAKR ELNASHAR

31. If soft markers: fetus-specific risk is calculated
NT thickness correctly identify 5 of 9 Down
syndrome cases
Other markers: less efficacious
Efficacy of 2nd T US: in screening for Down
syndrome in twins: uncertain.
ABOUBAKR ELNASHAR

32. A thickened nuchal translucency of 3.3 mm
ABOUBAKR ELNASHAR

33. 3. Congenital Malformations
Incidence:
1.2 to 2 times more common in twin.
Dizygotic twins
Rate/fetus is the same as in singletons
Monozygotic twins
rate is 2 to 3 times higher.
The most common structural abnormalities
cardiac
neural tube and brain
facial clefts
gastrointestinal
anterior abdominal wall.
ABOUBAKR ELNASHAR

34.  When:
18-22 w (II-2B)
45 minutes for the anomaly scan
ABOUBAKR ELNASHAR

35. Congenital anomalies unique to twin
1. Midline structural defects:
{twinning process}
 conjoined twins.
2. Malformations resulting from vascular events:
{placental anastomoses}: hypotension and/or
ischemia
Microcephaly
Periventricular leukomalacia,
Hydrocephalus
Intestinal atresia
Renal dysplasia
Limb amputation.
ABOUBAKR ELNASHAR

36. 3. Defects or deformities from intrauterine crowding:
 foot deformities
hip dislocation
Skull asymmetry
ABOUBAKR ELNASHAR

37. 4. SCREENING FOR PRETERM BIRTH
How:
Cervical length
When:
21-24 w
{correlates highly with PTL at < 32 to 33 w}
Risk of PTL is increased 3- to 5-fold from baseline
prevalence.
PPV: 22% to 38 %.
NPV: high: 94% to 96%.
ABOUBAKR ELNASHAR

38. CL > 35 mm at mid 2nd T: probability of reaching
34-35w is quite high (88% -98%).
Rate of cervical shortening
2.5 mm/w predicted PTL (positive likelihood ratio of 10.8).
Progressive shortening greater than expected
may indicate a higher risk of PTL.
ABOUBAKR ELNASHAR

39. There is still insufficient data to recommend
screening twin pregnancies with TVS cervical
length, but this might change soon!
(Schuit et al. 2014)
ABOUBAKR ELNASHAR

40. ABOUBAKR ELNASHAR

41. 5. ASSESSMENT OF FETAL GROWTH
The growth of twins:
In 1st and 2nd T:
not significantly different from growth of singletons
After 30W:
slower fetal growth
{placental crowding and more frequent anomalous umbilical
cord insertion}.
ABOUBAKR ELNASHAR

42. Growth discordance:
Difference in
1. EFW: range from 15% to 30%
EFW discordance of > 20%.
(SOGC)
2. AC: differences of > 20 mm.
 Increased fetal surveillance when:
 AC and/or EFW of one or both twins is < 10th
percentile or
 Growth discordance
ABOUBAKR ELNASHAR

43. Birth weight discordance formula:
ABOUBAKR ELNASHAR

44. Discordant growth” 20% difference in f weights or
AC difference of > 20 mm
There is a 2.5 cm difference in the AC measurements for twin A
and twin B, indicating 2nd trimester growth discordancy
ABOUBAKR ELNASHAR

45. 6. ASSESSMENT OF FETAL WELLBEING
Frequency:
Monochorionic twin
US/2-3 w, starting at 16-18 w
{early evidence of TTTS}.
Dichorionic twins
/3 w in 3rd T
{growth rate slows down after 30 to 32 w}.
Increased surveillance:
One or both fetuses show growth restriction or discordance.
In these circumstances, serial growth scans/2-3W
(or more frequently in monochorionic twins)
ABOUBAKR ELNASHAR

46. Fetal surveillance testing
1. Doppler
2. non-stress test, and/or
3. biophysical profile
ABOUBAKR ELNASHAR

47. 7. ASSESSMENT OF UMBILICAL ARTERY DOPPLER
{inequality of the 2 fetal-placental circulations can
cause inter-twin differences in growth}: umbilical
artery Doppler velocimetry may improve the
detection of IUGR or fetal growth discordance.
No clear benefit of Doppler velocimetry over the
use of US alone: routine use of Doppler velocimetry
in twin cannot be recommended.
ABOUBAKR ELNASHAR

48. 8. ASSESSMENT OF AMNIOTIC FLUID
Identification of the inter-twin membrane is vital
{determine the fluid space around each fetus}.
Methods:
Subjective
Objective:
Deepest vertical pocket,
Modified amniotic fluid index and
2-dimensional pockets.
ABOUBAKR ELNASHAR

49. Ascertain the presence of fluid, caudal and rostral:
determine to which fetus it belongs and subjectively
estimate if normal.
When AFV reduced or increased: vertical
measurement of the largest pocket in each sac
Oligohydramnios:
deepest vertical pocket < 2 cm
Polyhydramnios:
deepest vertical pocket is > 8 cm.
{These definitions correspond approximately to the 2.5th
percentile and 95th percentile across all gestational ages}.
ABOUBAKR ELNASHAR

50. This is also a common criterion used in defining
TTTS, and for these reasons, this may be the
clinically useful method for assessing
amniotic fluid in twins.
ABOUBAKR ELNASHAR

51. Twin-To-Twin Transfusion Syndrome
Incidence:
15% of MC
Pathology:
In MC placenta: vascular anastamoses.
Superficial and deep.
1) arterioarterial (AA)
2) arteriovenous (AV), or
3) venovenous (VV).
ABOUBAKR ELNASHAR

52. Blood from a donor
twin is transferred to a
recipient twin:
growth-restricted
discordant donor twin
markedly reduced
AF: "stuck."
ABOUBAKR ELNASHAR

53. Diagnosis
LateEarly
1. Polyhydramnios
2. An enlarged fetal bladder
1. Increased NT
2. Abnormal Doppler
of DV
3. Folding of inter twin
membrane can at 16w.
Recipient
1. Oligohydramnios
2. Severe oligohydramnios: amniotic
membrane is closely applied to the
fetus, which lies apposed to the
uterine wall (stuck twin).
3. Bladder can be barely visible
Donor
ABOUBAKR ELNASHAR

54.  .
Early
1. Increased NT
Three Fold increase in the risk for
Subsequent development of TTTS .
2. Inter-twin membrane folding
3. Abnormal Doppler of DV of the recipient
ABOUBAKR ELNASHAR

55. Pathognomonic sign:
stuck twin contained within the collapsed inter-twin
membrane {anhydramnios}.
Doppler studies
Umlical a of donor:
Absent or low end diastolic flow
Recipient:
decreased ventricular function depicted by tricuspid
regurgitation, reversal of A wave in ductus venosus,
and/or cardiac chamber enlargement in the recipient
are seen in more advanced stages of TTTS.
ABOUBAKR ELNASHAR

56. ….Stuck twin
ABOUBAKR ELNASHAR

57. Recipient Fetus
Polyhydraminos
Donor Twin
Severe Oligohydramnios
ABOUBAKR ELNASHAR

58. Quintero classification
determine the management plan for TTTS.
Stage 1 oligo-polyhydramnios sequence
Stage 2 absent bladder in the donor
Stage 3 abnormal fetal vascular Doppler studies
Stage 4 hydrops of one fetus
Stage 5 death of one fetus
ABOUBAKR ELNASHAR

59. ABOUBAKR ELNASHAR

60. Inter-twin membrane folding
(arrow = dividing membrane)
Polyhydramnios in g sac A
and oligohydramnios in g
sac B (arrow = dividing
membrane)
ABOUBAKR ELNASHAR

61. TTTS
ABOUBAKR ELNASHAR

62. Treatment
1. Reduction amniocentesis
SR:20-80%
Handicap:- 20%
Indication:- severe distressing
polyhydraminos
2. Selective laser ablation of
the placental anastomotic vs
SR:- 70-80%
Handicap:- 8%
Indication:- stage II and higher
ABOUBAKR ELNASHAR

63. Fetoscope and Laser ablation
ABOUBAKR ELNASHAR

64. 3- Septostomy
4- Selective cord coagulation
5- Radiofrequency ablation
ABOUBAKR ELNASHAR

65. 9. DIAGNOSIS OF RARE OBSTETRICAL
COMPLICATIONS UNIQUE TO TWINS
Monoamnionicity
Incidence:
1% of all monozygotic twin pregnancies.
Risk:
elevated risk of fetal death
{cord entanglement}.
improved double perinatal survival of 92% when
accurate prenatal diagnosis
serial sonography
antenatal testing
early identification is important
ABOUBAKR ELNASHAR

66. Diagnosis:
First trimester
Predict virtually all cases of monoamniotic twins.
1. Single yolk sac
2. Cord entanglement.
Second trimester:
1. Single shared placenta
2. Fetal phenotype concordance
3. Absence of inter-twin membrane
4. Adequate AF surrounding both fetuses
5. Free movement of both twins within the uterine cavity.
ABOUBAKR ELNASHAR

67. Twin Reversed Arterial Perfusion Syndrome
TRAP sequence, Acardiac twinning
Mechanism
most extreme manifestation of TTTS
umbilical arterial-to-arterial anastomosis
disruption of normal vascular perfusion
ABOUBAKR ELNASHAR

68. Incidence:
1 in 35 000 deliveries
1 in 100 monozyotic twins
1 in 30 monozygotic triplets
Risk:
PTL: 90%
congestive heart failure in the normal twin (also
called pump twin: 30%
 Perinatal mortality:
55% in this untreated cohort.
ABOUBAKR ELNASHAR

69. Diagnosis
1. MC twin:
absence of cardiac pulsation
poor definition of fetal parts.
2. Colour Doppler:
reversal of blood flow within the abnormal
fetus.
Blood-flow pattern reveals a paradoxical
direction of arterial flow towards rather than away
from the acardiac twin
retrograde flow in the acardiac twin’s abdominal
aorta.
ABOUBAKR ELNASHAR

70. TRAP Sequence
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71. ABOUBAKR ELNASHAR

72. Umbilical Artery Doppler of Acardiac Twin
ABOUBAKR ELNASHAR

73. Differential diagnosis
intrauterine fetal demise
An abnormal monochorionic twin
Placental tumours.
Evaluation:
1. Assess fetal hemodynamic function:
fetal echocardiography
hydrops in the pump twin: poor prognosis
2. Estimation of the weight ratio of the acardiac to
the pump twin
ABOUBAKR ELNASHAR

74. > 50%.< 50%< 70%≥ 70%
44%18%70%90%PTL
25%0%30%40%Polyhydramnios
94%35%10%30%F hydrops
ABOUBAKR ELNASHAR

75. TT:
1. Radio frequency ablation:
pump twin survival rate: 90%.
2. Occlusion of the blood flow to the acardiac twin
by ultrasound-guided diathermy of the umbilical
cord
3. Laser coagulation of the umbilical cord vessels
within the abdomen of acardiac twin, at about 16w
ABOUBAKR ELNASHAR

76. 4. Expectant management
Perinatal survival of the pump twin: 90%
Spontaneous cessation of flow in the acardiac twin
over time: 40%.
Because of the complexity of these cases and
the possible management options, including
expectant management, referral to a tertiary care
unit is indicated.
ABOUBAKR ELNASHAR

77. Conjoined Twins
Definition:-
Incomplete separation of monozygotic twins .
Embryology:-
Incomplete division of the embryonic disk at a
later developmental stage of the blastocyst (at least
13 days after fertilization) in a monozygotic twin
ABOUBAKR ELNASHAR

78. Incidence
1 in 50 000
1 in 100 000 births
1 in 300 monozygotic twin pregnancies.
The recurrence risk is negligible.
Sex ratio:
female > Male (2 : 1).
ABOUBAKR ELNASHAR

79. Classifications:-
according site of connection
1. Thoracopagus (thorax, 30–40%),
2. Omphalopagus (abdomen, 25–30%),
3. Pygopagus (sacrum, 10–20%),
4. Ischiopagus (pelvis 6–20%) .
5. Craniopagus (head, 2–16%).
ABOUBAKR ELNASHAR

80. Diagnosis
1st T.
1. Embryo appears bifid: follow-up imaging should
be performed to confirm the diagnosis.
2. Inability to separate the fetal bodies and skin
contours
3. lack of a separating membrane between the
twins
4. ≥ 3 vessels in the umbilical cord
5. Heads remaining at the same level
6. Body plane, extremities in unusual proximity
7. Failure of the fetuses to change their relative
positions over time.
ABOUBAKR ELNASHAR

81. Prognosis depends on :
• The location and the length of fusion .
• The presence of vital organs: liver and heart
in both twins.
Reasonable chance of survival
only omphalopagus
ABOUBAKR ELNASHAR

82. Single Fetal Death
50% of twin pregnancies identified in 1st T: 2 live
born infants.
Early in pregnancy:
prognosis for the surviving fetus is excellent.
2nd and 3rd T
2% to 5% of twin pregnancie
More common in
MC twins than in DC twins: 3-4 fold higher
HOMP: 14% to 17% of triplet pregnancies.
ABOUBAKR ELNASHAR

83. ABOUBAKR ELNASHAR

84. ABOUBAKR ELNASHAR

85. MCDCSequels of Death of Co-twin
15%3%Fetal Demise
68%54%Preterm Birth
34%16%Abnormal Postnatal Cranial Imaging
26%2%Neuro-developmental Impairment
Management depends on
1. Chorionicity
2. Gestation age
3. Time since death.
ABOUBAKR ELNASHAR

86. Surviving MC twin
Ischemic injury:
in the spleen, kidney, gastrointestinal tract, skin,
and brain
Up to 20%: neurologic injury: multicystic
encephalomalacia.
occur at the time of the demise
These abnormalities may not be diagnosed by US
until much later in pregnancy, far removed from the
ischemic event.
Immediate delivery may not prevent the
development of such complications.
ABOUBAKR ELNASHAR

87.  Surviving DC twin
Risk of major perinatal morbidity or mortality:
negligible, apart from the risk related to preterm
delivery.
ABOUBAKR ELNASHAR

88. 1. MC twin
The surviving fetus is at significant risk of
sustaining damage
{sudden, severe, and prolonged hypotension at the
time of the demise or by embolic later}
>34 w: Immediate intervention
32 to 34 W: corticosteroids & delivery after 48H
< 32 w:Conservative management
A. U/S, CTG, BPP
B. if normal: MRI of the fetal brain 2–3 w after
the co-twin death.
C. Counseling should include the long-term
morbidity in this condition
ABOUBAKR ELNASHAR

89. 2. DC
Death of one twin is not a strong indication for
intervention to deliver the surviving twin
A. Expectant management up to 37 w
B. If a condition affecting both twins is present
PET, IUGR: Close surveillance and timely
intervention
C. Regular assessment of coagulation status
ABOUBAKR ELNASHAR

90. Indications for Referral to an appropriate high-
risk pregnancy centre:
1. Twin-to-twin transfusion syndrome
2. Monoamniotic twins gestations
3. Conjoined twins
4. Twin reversed arterial perfusion sequence
5. Single fetal death in the second or third trimester
6. Growth discordance in monochorionic twins.
ABOUBAKR ELNASHAR

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