Ultrasound plays an indispensable role in managing multifetal gestations. It is crucial for determining chorionicity and zygosity early in the first trimester, as this predicts complications. Ultrasound can also assess nuchal translucency, screen for anomalies, monitor growth and detect complications like twin-twin transfusion syndrome that are more common in monochorionic twins. Serial ultrasound examinations are important for detailed evaluation of the placenta, umbilical cords, fetal growth and well-being in order to guide management and improve outcomes in these high risk pregnancies.

1. ROLE OF ULTRASOUND IN
MULTIFETAL GESTATION
What an obstetrician should know
?
DR BHARTI PANT GAHTORI
1 YEAR CERTIFICATE COURSE IN FIRST TRIMESTER
SCREENING, ANOMALY SCANNING & FETAL
DOPPLER, FMF APOLLO HOSPITAL, NEW DELHI
Special interest: Highrisk obstetrics,Fetal
Doppler,placental study & Fetal Echo. Gynae-infertility
ultrasound & Dopplers

2. INTRODUCTION
The term multifetal gestation includes twins, triplets &
higher-order multiples.
Incidence of dizygotic twins has increased
dramatically over few decades -
Increased maternal age of conception
 Increased use of ovulation induction(6-8%) agents
and gonadotropin in ART( 20-30%)
The incidence of monozygotic twins remains constant
throughout the world, at 1:250 pregnancies.
Perinatal mortality ~ 11% & morbidity rates are 5 - 7
times higher than singletons.
 6 times more likely to give birth preterm & 13 times
more likely to give birth before 32 wks of gestation

3. CHORION & AMNION

4. KEY TERMS
• ZYGOSITY - It refers to the type of conception &
the genetic make up of the pregnancy :
Monozygotic or dizygotic. Zygosity can only be
determined by genetic analysis of both foetuses.
• CHORIONICITY – It refers to the membrane
complement of the pregnancy and denotes the type
of placentation. In monozygotic, it is determined by
the occurrence, and timing of the embryo split.
Chorionicity, can be determined by non-invasive
USG
• AMNIONICITY- The number of amnions (inner
membranes) that surround fetuses .Pregnancies
with 1 amnion (so that all fetuses share 1 amniotic

5. ZYGOSITY
MONOZYGOTIC
• 1 ova +1 sperm =1
zygote
• ~25% of all twins
• Same sex & genetic
makeup
• Near identical
• Single or double
placenta
• DNA microprobe - same
DIZYGOTIC
• 2 ova +2sperm =2
zygote
• ~ 75-80 % of all twins
• Same or different sex &
Different genetic
makeup
• Fraternal
• Double or fused
placenta
• DNA microprobe-
different

6. CHORIONICITY
DICHORIONIC TWIN
 70% Dizygotic origin & 30%
monozygotic origin.
 If monozygotic origin,
splitting occurs < 3 days
PC
 There is complete
duplication of all cell lines
with formation of chorions,
amnions, yolk sacs, and
embryos
MONOCHORIONIC TWIN
 100% monozygotic origin
 Occurs when the split of the
developing structures
occurs > 3rd day PC. Three
variants-
 Monochorionic diamniotic
twins: 4th - 8th days PC
 Monoamniotic twins:
8th – 13th days PC
 Conjoined twins: embryo
split after 13th day PC, split
is incomplete; some
structures are duplicated
and some are shared.

7. 2 cell
cleavage
stage.
Blastocyst
stage
Implanted
blastocyst.
Formed
embryonic
disc

8. PATHOPHYSIOLOGY OF GENERAL
COMPLICATIONS INCREASING FETAL MORBIDITY
/MORTALITY
• Restraint in the capacity of uterus to
distend and permit adequate fetal growth,
thus creating risk for preterm labor.
• Doubling of the placental mass is
associated with obstetric complications of
preeclampsia & gestational diabetes. Risk
with singletons is 6.5%, twins is 12.7%, and
triplets is 20.0%
• Increased risk of abnormal placentation
and function leads to FGR that may also
add to the risk for preterm labor and birth

9. Why we want to diagnose multifetal
gestation & its chorionicity as early as
possible ??
Reason 2 = MC twins are associated with higher fetal risk (
30-50%) than DC twins(10-20%).Chorionicity is the most
important determinant of adverse fetal outcome in multifetal
gestation.
Reason 4 = The early the risk assessment & pick up of
various complications the easier it is to formulate individual
guidelines for screening, surveillance & management,
including the need of any interventional procedures as a part of
treatment.
Reason 3 = Ultrasound shows ~ 99% sensitivity in
assigning chorionicity at <14 wks, which reduces to 90% for
dichorionics & 77% for monochorionics at >14 wks, Early
pickup holds the key.
Reason1 : The higher the order of multiple gestation the
more severe & complicated pregnancy with higher chances of
maternal & fetal morbidity/mortality.

10. COMPLICATIONS SPECIFIC TO
MONOCHORIONICITY
• Increased risk of preterm labor & malformations than
Dichorionic & singletons .
• Deserve extra scrutiny due to conditions like
Monochorionic monoamniotic twin & conjoined twin.
There is a unique risk of
intra-placental vascular
connections causing
unequal distribution of
placental blood supply
between the fetal
circulations leading to
--twin-twin transfusion
syndrome (TTTS)
--twin reversed arterial
perfusion syndrome (TRAP)
&
An unequal placental mass
assignment due to the
unequal placement of the
vascular "equator" &
the intervening membrane
occurs. The fetus with a
smaller placental mass
becomes at high risk for.
-- discordant twin growth
-- selective fetal growth
restriction (sFGR), &
-- single fetal demise

11. MULTIFETAL
RELATED
UNIQUE TO
MONOCHORIONIC
MATERNAL
Prematurity X 6 TTTS , TRAP ,
TAPS
Preeclampsia x 3
Eclampsia x 4
Chromosomal &
structural anomalies
Monoamniotic &
conjoined twin
Diabetes/ HT
IUGR s-FGR & fetal
growth
discordance
APH & PPH X 2
Intrauterine fetal
demise
Co twin fetal demise Polyhydramnios
High order multiple Vasa previa &
velamentous cord
C - Section related
mortality

12. COMPARING COMPLICATION RATE

13. ULTRASOUND AS AN INDISPENSIBLE
TOOL
• An important tool in the armamentarium of
obstetrician & fetal medicine experts for managing
multifetal gestation.
• Ultrasound assessment of chorionicity is considered
the most crucial step. .
• It also helps in preterm & preeclampsia - risk
assessment & guides timely interventions.
• Predictive nature of ultrasound report eventually
safeguards us by default.
• All prenatal diagnostic, interventional & invasive
therapeutic procedures (fetoscopic laser photo-
coagulation & cord occlusion are lame without USG.

14. ULTRASOUND + DOPPLER AS A SCREENING TOOL
• Dating of pregnancy (determine GA)
• Determining chorionicity and amnionicity
• Twin labeling (assigning fetal location)
• Role of Nuchal Translucency as screening tool for
aneupoidy, early TTTS ,CHD etc
• Screening for structural abnormalities
• Screening of cervical length for preterm birth
• Detailed evaluation of placenta & mapping, umbilical
cord insertion site and its associated abnormalities.
• Doppler studies for screening high chances of
preeclampsia and fetal growth disturbances

15. ULTRASOUND + DOPPLER AS SURVEILLANCE
TOOL
• Diagnosis and serial surveillance of pregnancies
complicated by discordant fetal anomalies & single
intrauterine fetal demise.
• Fetal growth & amniotic fluid studies for screening,
diagnosis, monitoring & management of sFGR and
discordant growth.
• Ductus venosus in first trimester(assess CHD ,
TTTS)
• Doppler interrogation of the umbilical arteries (PI) ,
middle cerebral arteries (PI &PSV) & ductus
venosus (waveform) is used to diagnose & stage
 TTTS and TAPS
 monitor twins with growth discordance.

16. SPECIFICALLY IN
MONOCHORIONICS
Increased scrutiny needed for complications
associated with vascular anastomoses leading to
unequal sharing of placental blood supply & nutrients
- unique to this type of placentation .
• Ultrasound & doppler screening, diagnosis( staging)
monitoring & management of TTTS,TAPS & TRAP
sequence.
• Diagnosis , surveillance & management of
monochorionic
monoamniotic (MCMA) and conjoined twins.
• Ultrasound & Doppler Screening ,diagnosis, monitoring
&
management of sFGR, discordant growth & single fetal
demise.

17. STEP WISE APPROACH IN
ULTRASOUND ASSESSMENT OF
MULTIFETAL GESTATION
STEP 1. : How many are you
??STEP 2 : Dead or alive ??
STEP 3 : Where are you finally
located ??

18. STEP 4:What is your correct age ??
IDEAL GA ~ 11wks -
13wks
• If conceived naturally
,choose the larger of the
two CRLs to estimate GA
• In IVF pregnancy use
the oocyte retrieval date or
the embryonic age from
fertilization.
• If > 14wks choose the
larger head
circumference
Dating is done by
the CRL of the
bigger twin
Step 5: What is your type i.e
chorionicity & ??How to determine it

19. LESS THAN 10 WEEKS
USG findings that help in
determining chorionicity.
• the number of observable
gestational sacs
2 G sac = DCDA ,
1 G sac = MCDA)
• the number of yolk sacs
( Represent amnionicity)
2 yolk sac = diamniotic ,
1 yolk sac = monoamniotic)
• the number of visible
amniotic sacs within the
chorionic cavity
FIG 1- DCDA twins at 5wks3DAYs. Two round sonolucent sacs
with a brightly echogenic rim are clearly visible in the thick
decidua.
FIG 2- At 6wks a single chorionic sac is seen containing
two yolk sacs: S/O ? monochorionic twin pregnancy it is
not possible yet to diagnose amnionicity.
FIG 3- At 8wks MCDA twin pregnancy The two amnions
appear as thin echogenic membranes (arrows) close to
the two embryos, inside the chorionic cavity.

20. MORE THAN 10 WKS Step 1 – Check for number for
placental masses. Separate or
single ? If single rule out fused
dichorionic or monochorionic.
Step 2 - Identifying the lambda()
or (T) sign . The image CLEARLY
demonstrating the chorionicity should
be saved in the records for future
reference.
Step 3 - Carefully examine
dividing inter-twin membrane by
assessing its layers and
reflection.
Step 4 - Assess memb. thickness
at its placental insertion site.
Step 5 – During the same scan,
amnionicity should also be
determined and documented.
As yolk sac disappears ,
G-sac is no more
distinct & intertwin
membrane appears.
At this stage, a new set
of sonographic findings
will help determine
amnionicity/chorionicity.
These findings are
(1) placental number,
(2) chorionic peak sign
&
(3) membrane
characteristics

21. LAMBDA SIGN
CONFIRMS DICHORIONIC
FUSED PLACENTA
• Two placenta either
separate or fused = two
chorionic membrane
• Each fetus is surrounded by
an outer chorionic & inner
amnionic membrane which
get fused (CAAC) at one
point.
• The area from where these
chorionic layers emerge a
wedge gets created with
placental tissue in it referred
as the ‘lambda sign’. ().

22. TAU (T) SIGN
CONFIRMS
MONOCHORIONIC
PLACENTA
• Single placenta = single
chorionic layer
• This layer outlines fetal side
of placenta & entire
Gestational sac with fetuses
inside it
• Amniotic membrane
surrounds each fetus and
fuse (AA) in the middle to
form a thin separating layer
with no placental insertion
creating (T) sign.

23. INTERTWIN
MEMBRANE
•The membrane is imaged
perpendicularly to the
ultrasonic beam magnified
& measured .
•Cut off is 2mm.
•In DC twins It is formed
by four layers (amnion-
chorion-chorion-amnion). &
measures >2mm reflective
• In MC twins it has only
two layers (amnios-
amnios) measuring < 2mm
less reflective .

24. AFTER 14 WEEKS The reliability of using the
number of placental masses
becomes questionable in
late
gestation
 Always take note of other
parameters pointing towards
placental sharing.
 It is likely that using a
combination of ultrasound
features, rather than a
single
one, would be more
accurate.
 If facing difficulty in
assessing
(Chorion and amnion
already fused)
Step 1 - Try to follow the
above 5 steps and try to
pick out maximum
information
Step 6 - Add gender
evaluation, its
discordance assures of
dizygosity (and therefore
dichorionicity) in later
pregnancy.
ONLY 80-90%
ACCURACY
It is safer to manage the
pregnancy as monochorionic
if chorionicity is in doubt.

25. Step 6 :How comfortable are you with
each other ??(Labeling)
• Accurate labeling is essential
when prenatal diagnostic
testing & therapy is required
• Antenatal labeling of twins
according to laterality or
vertical orientation is reliable.
(CERVIX is used in CVS)
• GOOD PRACTICE to
describe each twin as fully as
possible e.g. (twin 1 is female,
on maternal left ,cephalic & has
anterior placenta), to minimize
the chance of confusion

26. STEP 6- Any one of you at risk of
Aneuploidy??
• 2- 2.5 times Increased risk of trisomy
• Relevance of nuchal translucency (CHD,TTTS,
triplets)
• Sensitivity of combined screening ~ 83% with
more
FPR so  chances of invasive testing.
• In DC twins – risk result assessed per fetus
• In MC twins – risk results assesses per
pregnancy
• Role of NIPT yet to confirmed

27. STEP 7: Are you prone to
malformations more than singletons
??
• Yes as MC twin 2-3 times > DC twin ~ singleton
• Apart from increased chances of cardiac , neural ,
GI
& abdominal anomalies There are 3 types of
congenital anomalies unique to twin pregnancies-
 Midline structural defects- conjoined twins
 Malformations resulting from vascular events
as a
consequence of placental anastomoses –
microcephaly ,hydrocephalus, intestinal atresia
 Defects or deformities from intrauterine
crowding-
Anatomic survey at the time of nuchal
translucency screening can identify several major
anomalies such as
anencephaly/holoprosencephaly, abdominal wall
defects,cystic hygroma etc . Abnormal cardiac
axis along with reverse ductus venosus & tricuspid
regurgitation in turn, identifies significant
congenital heart disease
 18-22 wks anomaly scan has its own value.

28. STEP 8 : Is your relationship with your
placenta cordial ??
• Check the cord insertion site ,there inter-distance
,placental location & any abnormalities
• Velamentous cord insertion increases the risk for
vasa previa and, in monochorionic twins, it is a
marker for unequal placental sharing and increased
risk for selective fetal growth restriction. Check for
cord entanglement .
• Check for placenta previa , circumvallate placenta
abruptio and intra placenta anastomoses.

29. • Serial ultrasonography is the most accurate method to
assess fetal growth in cases of multiple gestation.
• Intrauterine growth of twins is similar to that of singletons
until 30 to 32 weeks’ gestation, when the abdominal
circumference measurements of twins begin to lag behind
those of singletons.
• There is no separate chart to assess the growth curve for
multifetal gestation, singleton growth chart is followed..
• Negate all conditions like fetal abnormality , infections,
TTTS before specifically diagnosing lag in growth potential
as the main cause of growth restriction.
• FETAL DOPPLER IS THE DIFFERENTIATING AND
MONITORING TOOL OF SUCH CONDITION.
STEP 9 : How are you growing ?? I
hope you are well nourished ??

30. STEP 10 – Is my cervix strong enough
??
IN ASYMPTOMATIC WOMEN
•Cervical length screening in twin
pregnancies as a predictor of
spontaneous PTB from 18 weeks
of gestation. Cut off – 3cm
REPEATED MEASURES OF
CERVICAL LENGTH NOT
NEEDED.
IN SYMPTOMATIC WOMEN
•Cervical length measurement had
a low predictive accuracy for PTB
at <34 weeks of gestation but
cervical length – 2.5 cm asks for
hawk eye and start of
progesterone..

31. DOPPLER MEASUREMENTS
• In each scan along with fetal growth (HC, AC,FL), amniotic
fluid (deepest vertical pool), assessment
• Assess PI by Doppler (umbilical artery, middle cerebral
artery and ductus venosus) and in monochorionic twins
middle cerebral artery PSV to detect possible twin anemia–
polycythemia sequence (TAPS) or fetal anemia condition.
• Management depends on-
• sFGR & Growth discordance - EDF of Umbilical A. , MCA
PI and ductus venosus PI
• TTTS - EDF of Umbilical A. , MCA PI , ductus venosus PI &
umbilical vein PI of donor & recipient
• TAPS – Middle cerebral A. peak systolic velocity (PSV) of
both Donor & recipient .
• TRAP – Blood flow of the inter anastamosing vessel is done.

32. DICHORIONIC DIAMNIOTIC TWINS(DCDA)
RECAP
SUMMARY
DCDA pregnancies
account for the majority
(~76%) of all twin
pregnancies.
They account for all
dizygotic pregnancies and
(~20%) of monozygotic
pregnancies.
Pathophysiology
 DIZYGOTIC.
 MONOZYGOTIC(
splitting
~1-3 days post
fertilisation (morula)
ULTRASOUND FINDINGS
Presence of two distinct
gestational sacs with
each sac having embryo
& yolk sac with outer
chorion & inner amnion
surrounding each embryo
A thick inter-twin
membrane 2C+2 A
Thick membrane
between two sacs-
Lambda sign twin peak
sign
 Discordant sex

33. DCDA TWIN
MONITORING
•Scans at 12, 20 weeks
and then every 4 weeks
until delivery.
•If there is discordance in
fetal size of >15%,
discordance in amniotic
fluid or any abnormal
Dopplers then review
every 1 week.
•If there is no
complication, consider
delivery at 37 weeks.

34. FETAL COMPLICATIONS IN DCDA
TWINS
Lowest rate of complications amongst twin
pregnancies though more than singleton .Such
recognized complications include:
1)Increased risk of preterm labor and perinatal risk of
prematurity
2) Increased risk of intrauterine growth restriction
(IUGR)
3) placenta-related problems
– increased risk of velamentous cord insertion
– increased risk of marginal cord insertion
– increased incidence of placenta previa spectrum

35. MONOCHORIONIC DIAMNIOTIC TWIN -RECAP
SUMMARY
• MONOZYGOTIC SUBTYPE
with a single chorionic sac (
later placenta) but have
two amniotic sacs and two yolk
sacs.
Epidemiology
• It accounts for the vast majority
(~70-75%) of monozygotic twin
pregnancies although only
~30% of all twin pregnancies.
The estimated incidence is at
~1:400 pregnancies .
Pathology
• An MCDA pregnancy results
from a separation of a single
zygote at ~4-8 days (blastocyst
ULTRASOUND FINDING
• Shows a twin pregnancy
with a single gestational
sac, 1 Chorion with 2
amnions and 2 separate
yolk sacs
• A thin inter-twin dividing
membrane - must be
identified
• T sign seen ( negative
lambda sign) suggestive of
single placenta
• Almost always two
separate yolk
sacs (differentiating from

36. MONITORING IN
MCDA TWINS
•Scans at 12 and 16
weeks and then every 2
weeks until delivery.
•Doppler blood flow
studies
- UA, UV, DV and MCA PI
& PSV baseline 20 weeks
•If there is discordance in
fetal size of >15%, in
amniotic fluid or any
abnormal Dopplers then
review every 1 week.
•If there is no
complication, consider
delivery at 36 weeks

37. COMPLICATIONS SPECIFIC TO
MONOCHORIONICITY
• Increased risk of preterm labor & malformations than
Dichorionic & singletons .
• Deserve extra scrutiny due to conditions like
Monochorionic monoamniotic twin & conjoined twin.
There is a unique risk of
intra-placental vascular
connections causing
unequal distribution of
placental blood supply
between the fetal
circulations leading to
--Twin-twin transfusion
syndrome (TTTS)
--Twin reversed arterial
perfusion syndrome (TRAP)
&
An unequal placental mass
assignment due to the
unequal placement of the
vascular "equator" &
the intervening membrane
occurs. The fetus with a
smaller placental mass
becomes at high risk for.
-- Discordant twin growth
-- Selective fetal growth
restriction (sFGR), &
-- Single fetal demise

38. COMPLICATION COMMON TO ALL
TWIN SUBTYPES
• PRETERM LABOR & DELIVERY
• FETAL GROWTH RESTRICTION &
GROWTH DISCORDANCE
• MALFORMATION IN ONE FETUS
• SINGLE FETUS DEMISE

39. PRETERM LABOUR
& DELIVERY
MANAGEMENT:
• If h/o preterm in the past ,
present pregnancy is MC with
chances of TTTS etc , or high
order multiple Start cervical
length assessment at 16 wks :
• In asymptomatic women, a
cervical length ≤20 mm at 20–24
weeks was the most accurate
predictor of preterm birth before
32 and before 34 weeks
• If cervical length 2.5 – 3cm
then start vaginal progesterone
200mg
& monitoring every 2-3 wks
• If cervical length less than 1.5
cm go for cerclage
INCIDENCE: 20%–75% in
multiple gestations.
3 fold increased morbidity
AETIOLOGY:
•Intrauterine infection,
•Cervical insufficiency
•Increased uterine
stretch/distension.
•  Corticotrophin‐releasing
hormone (CRH) from the
larger placental mass
INVESTIGATION: Cervical
length assessment b/w
18-24wks

40. SELECTIVE FGR WITH GROWTH DISCORDANCE
 10% of dichorionics twins & 10-15% of monochorionic twins.
Investigations:
Detailed ultrasound examination.
Ultrasound scans every 1 week to monitor growth, amniotic fluid
volume & pulsatility index in the umbilical A.,middle cerebral artery
& ductus venosus of both fetuses.
If in the presence of ≥25% estimated weight discordance between
the fetuses there is polyhydramnios in the sac of the bigger twin the
condition is sFGR with superimposed TTTS
 No chances of recurrence seen.
 No associated genetic or chromosomal ab. seen.
MANAGEMENT
Types I and II with TTTS: endoscopic laser ablation of communicating placental
vessels
Type I without TTTS: Expectant management with close monitoring .If Doppler
normal then elective cesarean section at 34-35 weeks. There is intact survival of
both twins in 95% of cases.
Type II without TTTS: there is a high risk of perinatal death and handicap for both
twins.
≥26 weeks: the best management is close monitoring and delivery if the ductus
venosus EDF becomes negative or reversed.
<26 weeks: the best management is endoscopic laser ablation of
communicating placental vessels. Survival of the big baby is 70% and of the
small baby depends of ductus venosus EDF: 40% if positive and 10% if negative or
reversed. Risk of neonatal cerebral lesions primarily depends on gestational age at
delivery and varies from 20% for birth at <26 weeks to 5% for birth at ≥32 weeks.
An alternative management is cord occlusion of the small fetus; the survival of
the large twin is 90%.
Type III: the two umbilical cords are adjacent to each other and the behaviour of the
pregnancy is similar to that of monoamniotic twins; development of TTTS is rare
and sudden unexpected death could occur in 20-30% of cases. Laser surgery may
be impossible and the best management is close monitoring and delivery on the
basis of ductus venosus EDF in the small fetus. If the ductus venosus EDF is
positive elective delivery should be by cesarean section at 32 weeks’ gestation.

41. MALFORMATION IN
ONE TWIN
Management options-
a) Expectant ( > risk for PTD)
b) Termination of entire
pregnancy
c) Selective termination of
anomalous fetus depends on
chorionicity
If diachorionic
i) Intracardiac KCL as early
till 20wks
If monochorionic ( cord
occlusion)
i) Interstitial laser ( <13wks)
ii) In later gestation – Bipolar
cord coagulation else
Radiofrequency cord
Management is influenced
by-
CHORIONICITY
then
a) The type of abnormality
–lethal , impending death
due to severe IUGR or non
lethal but problematic
b) Whether or not it is
concordant
c) The GA when
diagnosed
d) Expectation of the
patient

42. SINGLE FETAL
DEMISE Spontaneous death of one fetus
occurs in 1% of MC twins.
ETIOLOGY
Discordant infections, discordant
structural congenital anomalies and
discordant fetal growth.
 Placental factors involved in
sIUFD include uneven placental
sharing, placental implantation
anomalies, and peripheral cord
insertion
Death of one twin is associated
with acute hemorrhage from the co-
twin into the fetoplacental unit of the
dead one. In the co-twin there is a
15% risk of death and ≥ 25% of the
survivors have severe neurological
injury. There is also a high risk (60-
70%) of preterm birth.
ULTRASOUND
MONITORING
This should include
assessment of fetal
Doppler, especially MCA-
PSV, in order to look for
signs of fetal anemia in
the surviving twin.
MRI after 3 weeks of fetal
death to assess changes
in the brain sec. to
hypotensionhypovolemi
a ischemia
MANAGEMENT
Management therefore depends on chorionicity and gestational age.
Dichorionic gestation:
<12 weeks: Usually no consequences, so no intervention needed.
>12 weeks: Immediate delivery has no benefit for the remaining fetus
and the often-quoted maternal risk has not been demonstrated.
There is 57% chances of preterm delivery before 34 wks in of surviving
twin
Monochorionic gestation:
<12 weeks: Associated with high risk of loss of other twin with no
intervention studied.
>12 weeks: Associated with about 10% risk of intrauterine death and
additional 25% risk of neurologic complications in other twin.. At the
time the demise is discovered, the greatest harm has most likely
already occurred in the remaining fetus, and there seems to be no
benefit in immediate delivery, especially if the surviving fetus(es) are
very preterm and otherwise healthy. In such cases, allowing the
pregnancy to continue may provide the most benefit. The
coagulopathy risk for the mother is minimal, probably <2%.

43. MONOAMNIOTIC TWINS  1% of all Monozygotic
twins.
 One G sac ,one chorion
,one amnion , one yolksac &
two embryo.
They result from splitting(7-
13) days after fertilization.
ULTRASOUND FEATURES –
•· Single placenta & same sex
•· Close approximation of the
cord insertions (<5cm)
•· Entanglement of the cords;
•· Normal and identical
AFV around both fetuses;
•· Unrestricted fetal
movement;
•· Absence of a dividing
membrane demonstrated on
two studies 24 hrs apart
• two distinct arterial waveform
with different heart rates within
the same sampling gate
•· A single yolk sac may be a
DIFFERENTIAL DIAGNOSIS
• Conjoined twins
• TTTS stuck twin
• Twin demise
•One twin with Renal abnormality so oligo
• PPROM or intertwin membrane rupture due to
interventions
MONITORING & MANAGEMENT
•Scans at 12 and 16 weeks and then every 2 weeks until
delivery.
•Watch for cord entanglement ,single fetal demise,
malpresentation
•If there is discordance in fetal size of >15% or any
abnormal Dopplers then review every 1 week.
•If there is no complication, delivery by cesarean section at
32 weeks.

44. CONJOINED TWINS
Prevalence:
1% of monochorionic twins.
Results from incomplete splitting of
the embryonic mass after day 13 PC.
Associated abnormalities:
The incidence of chromosomal
abnormalities and genetic syndromes
is not increased.
Investigations:
Detailed ultrasound examination and
assessment by multidisciplinary team.
Management:
Pregnancy termination, stillbirth or
neonatal death in >90% of cases.
If the pregnancy continues, delivery
should be by cesarean section in a
expertise centre
Prognosis:
Very high risk of handicap in
survivors.
Recurrence:
No increased risk of recurrence.
ULTRASOUND DIAGNOSIS:
Fused twins in MCMA pregnancy.
Classified according to the site of
fusion .Most common type is
thoracopagus (75% of cases)
with fusion in the thorax and
abdomen and often conjoined
hearts, livers and intestines.
Other types include pygopagus
(fetuses fused at the rump),
ischiopagus (fetuses fused at the
lower half of the bodies with
spines conjoined end to end at
180o angle), craniophagus (fused
skulls and separate bodies),
omphalopagus (fused at the
lower abdomen, with shared liver
and intestines).

45. TWIN – TWIN TRANSFUSION
SYNDROME (TTTS)
 Complicates 10-15% of
(MCDA) twin. If left untreated
60-70%mortality.
The syndrome is caused by
unbalanced blood flow from
the donor to the recipient
through placental
anastomoses. AV>AA
Investigations:
 Detailed Ultrasound to rule
out anomaly ,then scans every
1 week to monitor growth,
cervical length, AFV and
pulsatility index in the umbilical
artery, middle cerebral artery
and ductus venosus of both
MANAGEMENT
 Only Discordance in amniotic fluid (not fulfilling Oli/poly criteria & normal fetal
Doppler:
Overall survival: 95%. Progression to TTTS: 15%.
Ultrasound scans every 1-2 weeks to monitor evolution.
 Stage 1:
Survival: overall 85%, at least one twin 90%. Progression to stages 2 to 4: 20%.
Ultrasound scans every 1 week to monitor evolution.
Endoscopic Laser Ablation of communicating placental vessels if progression to
stages 2-4 or increasing polyhydramnios and shortening of cervical length.
 Stages 2-4:
<28 weeks: ELA of communicating placental vessels; all communicating vessels should
be ablated and the area between them should also be coagulated to achieve
dichorionization of the placenta. If facility not available then amnioreduction.
≥28 weeks: the best option is to deliver by cesarean section and the timing would
depend on the Doppler findings in the umbilical artery and ductus venosus of both
fetuses.
Stage 2: survival overall 75%, at least one twin 85%.
Stages 3 and 4: survival overall 60-70%, at least one twin 75-85%.
Neurodevelopmental impairment in survivors: 5-10%.
 Follow-up after laser therapy: ultrasound scans and Doppler every 1 week until
resolution of the signs of TTTS and normalization of Doppler findings and every 2 weeks
thereafter with special attention for signs of brain damage, recurrence of TTTS and
development of TAPS.

46. TWIN ANEMIA –
POLYCYTHEMIA
SEQUENCE
Prevalence:
Spontaneous: 5% of MC twins.
Usually occurs >26 weeks'
gestation.
After laser ablation of
placental vessels: 2-10% of MC
twins..
Etiology :
TAPS occurs due to a slow
transfusion of blood from the
donor to the recipient through
few very small arterio-venous
vascular anastomoses leading
to highly discordant hemoglobin
levels
There is no substantial
difference between the twins in
either size or AFV
ULTRASOUND FINDINGS-
PLACENTA- anemic fetus looks
thick and hyperechogenic,
polycythemic fetus looks thin and
translucent.
 The fetal (MCA PSV) in the
anemic fetus is increased (>1.5
multiples of median), whereas that
in the polycythemic fetus is
decreased (<1 multiples of the
normal median).
 The anemic fetus may have a
dilated heart, tricuspid regurgitation
and ascites.
Investigations:Detailed ultrasound
examination, including echo (to
assess cardiac function) and
measurement of MCA PSV
(to predict degree of anemia and
polycythemia).
MANAGEMENT:
<26 weeks: Endoscopic laser ablation of communicating
placental vessels. Subsequently, scans every 1 week to
monitor fetal growth, brain anatomy and MCA-PSV. Fetal brain
MRI at ≥32 weeks’ gestation should be considered for the
diagnosis of neuronal migration disorders. If both babies are
developing normally vaginal delivery can be carried out at 37
weeks.
26-30 weeks: intrauterine blood transfusions to the anemic
twin and exchange transfusion with Hartmans’ solution for the
polycythemic twin. Doppler assessment every 2-3 days
because it may become necessary to undertake
interventions every 3-4 days. Delivery by cesarean section
at 30-32 weeks.
>30 weeks: delivery by cesarean section.
PROGNOSIS:
Neurodevelopmental delay in up to 20% of cases, which

47. TWIN REVERSE ARTERIAL
PERFUSION ( TRAP)
 2-3% of monochorionic twins.
Pathogenesis:I
First, abnormal cardiac
embryogenesis occurs between
8 to 12 weeks in one of the two
twins .
Second, a specific abnormal
placental angioarchitecture.
The size of the acardiac mass
is prognostic value for the
survival of the pump twin.
About 50% of pump twins die
before or after birth from
congestive heart failure or
severe preterm birth, due to
polyhydramnios.
ULTRASOUND DIAGNOSIS :
MC twins with one normal fetus
(pump twin) and another with no
cardiac acitivity (rarely, a
rudimentary heart may show slow
pulsations) and variable degrees of
deficient development of the head
and upper limbs and hydrops
(recipient twin).
 PATHOGNOMIC SIGNS: Color
Doppler demonstration of seemingly
paradoxical arterial blood flow
toward, rather than away from, the
acardiac twin; reversal of arterial
blood flow.
Echocardiography to assess
cardiac function in the pump
twin.
MANAGEMENT
Fetal therapy:
•Prenatal treatment is by occlusion of the blood flow to the acardiac twin. Several
methods have been used, including ablation of umbilical cord vessels by laser or
diathermy, coagulation of placental anastomoses by laser, or ablation of intrafetal
vessels by monopolar diathermy, laser, or radiofrequency.
•When these methods are used at 16-18 weeks’ gestation the survival rate of the
pump twin is about 80%.
The preferred management is ultrasound-guided laser coagulation or radiofrequency
of the umbilical cord vessels within the abdomen of the acardiac twin at 11-13 weeks.
The survival is 70-75%, which is less than the 80% achieved with intervention at 16-18
weeks.
However, delay in intervention between the diagnosis of TRAP sequence at 11-
13 weeks’ gestation until 16-18 weeks is associated with spontaneous cessation
of flow in the acardiac twin in 60% of cases and in about 50% of these there is
also death or brain damage in the pump twin.
Follow up:
Intrauterine intervention: scan in 1 week to confirm that the pump twin is alive and that
there is cessation of flow in the acardiac twin. Subsequently, standard follow-up.
No intrauterine intervention: scans every 2-3 weeks to monitor growth of the acardiac
twin, heart function of the pump twin and amniotic fluid volume.
Delivery:
Standard obstetric care and delivery.
Prognosis:
Depends on gestational age at birth.

48. INVASIVE TESTING IN TWINS
 Pregnancy loss rate is 3–4%, risk of post 2nd trimester
miscarriage is ~1%.
 In invasive testing, Both DC twins have to be sampled But in
monochorionics as per indication.
 In DC twins, CVS is preferred for early diagnosis of
aneuploidy
and plan low risk first trimester selective termination.
 For amniocentesis, both single and double uterine entry
techniques are described, Single entry not to be attempted
in
MCDA twins .
 When MC twins have discordant anomaly, prior to invasive
testing ,explain the complexity of selective termination if
needed.
 NIPT( Cell-free fetal DNA testing ) is used for aneuploidy
screening in singleton pregnancies with detection rates
(>99%

49. INTERVENTIONAL PROCEDURES
• FETAL REDUCTION
• SELECTIVE TERMINATION
• AMNIOREDUCTION
• SEPTOSTOMY
• CORD OCCLUSION
• FETOSCOPIC GUIDED LASER
PHOTOCOAGULATION

50. TIMING OF DELIVERY

51. TRIPLETS & HIGHER
ORDER PREGNANCY
• Triplet pregnancies result
from various fertilization,
splitting, and development
scenarios that involve ova and
sperm. Triplets can be
A)Trizygotic triplets : When
three sperm fertilize three ova.
B)Dizygotic triplets : develop
from one set of monozygotic
cotriplets and a third cotriplet
derived from a different zygote.
C) Monozygotic triplets : Two
consecutive zygotic splittings
with a vanished fetus can also
result in monozygotic triplets.
•Triplets and higher-order
multiples accounted for 13.8
out of 10,000 pregnancies in
2010.They rose drastically
during mid eighties due to
ART
•Less than 7% of higher-
order multiples result from
spontaneous ovulation .
Zygosity in quadruplets and
higher order multiples also
varies.

52. MANAGEMENT
• NT is the only option to assess aneuploidy risk. There is
no
role of serum screening or NIPT in triplets & higher.
• In triplet pregnancies diagnosed during the first trimester
management options include continuing with the whole
pregnancy or embryo reduction (ER) to twins or singletons.
• Assessment of chorionicity is very important for planning
embryo reduction & further monitoring and management
especially those with monochorionic origin.
• A very detailed USG evaluation of malformations & growth
parameters as well as scrutiny for TTTS is needed after
16wks
• The triplet pregnancy if continued has all maternal & fetal
complications sameas twins but with more severity and
morbidity.
• Prophylactic Cerclage is not proposed , but tocolytics

53. SUMMARY
• Constitute 2-3 % of all pregnancies
• There are 70-80% dichorionic and 30% monochorionic
• All Dizygotic are dichorionic but all monozygotic are 30%
dichorionic , 69% monochorionic and 1% monoamniotic.
• High perinatal morbidity mortality with preterm risk.
• Early Determination of chorionicity is a must
• "THERE IS NO DIAGNOSIS AS SIMPLY TWINS.”
“The only diagnosis is a monochorionic or dichorionic twin
gestation. This should be written in capital red letters on the
front of the ANC file at 8 - 10 weeks".
• Monochorionic twins are marred by high adverse fetal
outcome due to placental anastomoses and unequal
nutrient sharing.

54. SUMMARY
• If difficulty in determining chorionicity, try TVS , else refer
to higher centre for confirmation, else manage as
monochorionic twins.
• Offer combined screening for aneuploidy risk assessment
.Else NT is reliable.
• Early dating , labeling & detection of anomalies
• Embryo reduction after 12 weeks (< 16 weeks)
• No role of NIPT No role of triple/quadruple marker
• More frequent monitoring in MC twins
• Look for complications in monochorionics.
• Use doppler to assess placenta and cord abnormalities.
• Monitor for maternal complications as well.

55. TAKE HOME MESSAGE
• Insist that chorionicity is reported in every scan. If
unable to decipher send to experts for the same. If
not possible manage as monochorionic twins
• First trimester chorionicity assessment -100%
accurate
Second trimester - 97%
 lambda sign
membrane
thickness
position of
placenta
 fetal sex
Third trimester - difficult
 separate

56. WHEN TO REFFER
1st trimester diagnosis of monochorionicity with features of
its complications -
• Raised Nuchal translucency of one twin with discrepant
amniotic fluid ( s/o TTTS)
• Difference in CRL > 15%
• Single amnion with one yolk sac & entangled cord ( s/o MA
twin)
• Single amnion with crowded fetal parts ( s/o conjoined twin)
2nd trimester appearance of complicating features-
• Features of oli/poly,absent bladder &abn. dopplers s/o TTTS
• Single fetal death in the 2nd & 3rd trimester as associated
with adverse neurological outcomes, such as multicystic
encephalomalacia, occurs in ~ 18% of surviving twins & 12%
risk of co twin death.
• Growth discordance in (intertwin growth-discordance >18% )
• Higher order multiple gestation.