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Monash Health Advanced Obstetric Ultrasound Update

MCDA twins identification and Surveillance

Dr Mark TeohFetal Diagnostic Unit

Obstetric Ultrasound Scan (Less than 12 weeks). Indication: Early dating LMP EDD 24/12/2019

Twin A: CRL 10mm = 7w 1d; FHR 138bpm; Yolk NAD; US EDD 30/12/2019Twin B: CRL 8mm = 7w 1d: FHR 127bpm; Yolk NAD; US EDD 30/12/2019

Conclusion:DCDA twin pregnancy. EDD based on Ultrasound in concordant with LMP EDD.

Obstetric Ultrasound Scan (12 weeks). Indication: 12 scan, twin pregnancy

EDD by LMP: 24/12/2019GA by LMP: 12w 6d

There is a live intrauterine twin pregnancy, dichorionic, diamniotic. Limited anatomy survey normalTwin A: CRL 57mm = 12w 1d; FHR 152bpm; US EDD 29/12/2019; NT 16mmTwin B: CRL 58mm = 12w 2d: FHR 127bpm; US EDD 28/12/2019; NT 17mm

Conclusion:

Live intrauterine DCDA twin pregnancy with estimated EDDs of 29/12/2019 and 28/12/2019. Normal

early morphology assessment.

First Ultrasound:Early T1 Ultrasound report

Second Ultrasound:T1 anatomy Ultrasound report

Obstetric Ultrasound Scan Twins (20-22 weeks). Indication: DCDA twins morphology scanEDD: 28/12/209

Report:EFW T1 488g +/- 15%; EFW T2 466g +/- 15%These appear to be MCDA twins with stage 1 TTTS (thin dividing membrane). AF discordance of 14cm and 2.7cm for Twins 1 and 2 respectively. MCA PSV concordant 37cm/s (1.3 MoM) and 25cm/s (0.86 MoM).Placenta upper anterior.

Conclusion:

MCDA twins at 22w 0d with stage 1 TTTS. Single upper anterior placenta. Referred to Monash for

further management.

Third Ultrasound:T2 anatomy Ultrasound report

Tertiary Ultrasound:

TTTS assessment

Massive polyhydramnios Amnioreduction

SROM leading to Labour and

delivery

Double Neonatal

Death

Message

• Incorrect identification of monochorionicity may lead to poor outcomes

• Correct identification of monochorionicity is key in management of Monochorionic twins.

Monozygous twinsDCDA 15% - early split <d3

MCDA 85% - later split d3-8

MCMA 1% – latest split d8

Dizygous twins

Chorionicity = number of placentae

DCDA obligates – no split

• One CL = MZ twins

• Less useful if IVF pregnancy due to multiple CL

DCDA thick ITM

Echogenic chorion

between 2 leaves of

amnion

MCDA thin ITM

No echogenic chrion

between 2 leaves of

amnion

Lambda λ sign

echogenic chorion

between 2 leaves of

amnion

T-sign

no echogenic chrion

between 2 leaves of

amnion

Ultrasound of chorionicity – first trimester

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Placenta count Lambda λ or T-sign*

•Membrane thickness*

Corpora Lutea count °

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• Accuracy of prediction approaches 100%• Prospective study to predict chorionicity with ultrasound at 10 to 14 weeks• Confirmation by postnatal placental histopathology

Carroll et al, BJOG 2002

Sonographic signs in the prediction of dichorionic and monochorionic twin pregnancies. PPV and NPV = positive and negative predictive values, respectively.

Ultrasonographic findings Sensitivity % Specificity % PPV % NPV %Dichorionic signsλ or separate placentae (n= 150) 97.4 100 100 91.9ITM ≥1.5mm (n= 140) 92.6 100 100 80λ or separate placentae and/or ITM ≥1.5mm (n= 140) 99.1 100 100 96.9

Monochorionic signsT (n= 150) 100 98.2 94.4 100ITM <1.5mm (n= 140) 100 92.6 80 100T and/or ITM <1.5mm (n= 140) 100 91.6 78 100

*All P values < 0.0000001

Ultrasound of chorionicity – first trimester

Ultrasound of chorionicity – early

first trimester• 8 weeks

Ultrasound of chorionicity – first

trimester• 12 weeks

Chorionicity=

First Trimester Diagnosis

Ultrasound of chorionicity

Ultrasound of amnionicity

• Ultrasound featureo Single amniotic sac

• Fetuses changing positions • No intertwin membrane

o Cord entanglement• Described as early as 10 weeks• Use pulsed Doppler – “bifid”

o Yolk sac number• 2 predicts diamnionicity• 1 not predictive of monoamnionicity• Not useful

Labeling of twin fetuses

Encourage:• Use reliable, consistent strategy using

individual characteristics*:o Location –left/right; upper/lower#

o Placental positions

o Cord insertion locations

o Gender

o Smaller/larger

o Recipient/Donor if TTTS

• MCMA – unreliable

*2016 Khalil UOG #2011 Diaz

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MC v DC outcomes

2007 Hack BJOG

Monochorionic* Dichorionic Statistical significance

Gestation 35w 4d 36w 5d P <0.001

Perinatal mortality 12% 5% P <0.001

Birthweight 2060 2282 P <0.001

BW discordance >20% 30% 25% P 0.094

NICU admission 30% 20% P <0.001

NEC 4% 1% P <0.001

IVH 6% 4% P 0.07

*MC twins necessitating fetal intervention excluded therefore difference probably underestimate

Monochorionic Placenta

• Intertwin Anastomoses • Vascular Equator

• Single Placental Mass

TTTS• Large AV

anastomoses• Net unidirectional

flow• Some AA and VVs

TAPS• Few miniscule AV

anastomoses• No AAs and VVS

sIUGR•Unequal

placental share•Growth

discordance

• Placental share

Least CommonCommonest Complications

Natural History• MZ twinning rate 1 in 500 pregnancies (IVF 2 – 3x higher chance)

10 to 15% develop severe TTTS90% mortality untreated

~1 in 5000 develop TRAP30% chance of harm to normal

10 to 15% develop sFGRSignificant morbidity/mortality risk

3 to 15% develop TAPS Significant morbidity/mortality risk

2% discordant anomaliesSignificant morbidity risk

Specific MC complications

Twin-twin Transfusion Syndrome (TTTS)

Selective Fetal Growth Restriction (sFGR/sIUGR)

Twin anemia-polycythemia Sequence (TAPS)

Twin reversed arterial perfusion syndrome (TRAP)

Discordant congenital anomaly

1 in 3 MC twins will develop:

1. TTTS2. sFGR or sIUGR3. TAPS

Frequent monitoringPIVOTAL

for detection

Monochorionic Twin Monitoring

• Early detection and management of specific MC twin complications

• Early detection and management of single twin demise

Aim

What Ultrasound parameters ?

First trimester

• Chorionicity• Amnionicity• Dates• NT difference• Placenta Cord insertion• Anatomy

Second and third Trimester

• Biometry• Amniotic Fluid (DVP)• Umbilical Artery Doppler• Middle Cerebral Artery Doppler• Ductus Venosus Doppler• Activity• Fetal Bladder Different Amniotic Fluid Echogenicity

Different Sac

“Mesentery like”Membrane Fold

Stuck TwinDefying Gravity

TTTS

Quintero (1999) Ultrasound Feature

One AF discordance (<2cm D, >8cm R)

Two Empty Donor Bladder

Three Abnormal Dopplers -A/REDF, Rev DV, UV

Four Hydrops

Five Demise of one fetus

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“Starry sky” liverDecreased parenchymal echogenicity• Due to polycythemiaEchogenic portal venules• Appearing like “stars”

TAPS

Stage Ultrasound Findings

One MCA-PSV donor >1.5MoM,recipient <1.0MoM

Two MCA-PSV donor >1.7MoM, recipient <0.8MoM

Three As per S2 and critically abnormal Dopplers°

Four Donor Hydrops

Five IUFD preceded by TAPS

°AREDF, pulsatile UV, increased PI in DV or reversed DV flow

Placental morphologyAnemic placenta• Echogenic, thick Polycythemic placenta• Hypoechoic, thin

Twin Anemia Polycythemia Sequence

FIGURE 2(Colour online) Ultrasound image of a TAPS placenta showing a difference in placental thickness and echodensity. On the left side ofthe image the hydropic and echogenic placental share of the anemic donor and on the right side the normal aspect of the placenta ofthe recipient is depicted.

FIGURE 3(Colour online) Ultrasound image showing a starry sky liver in a TAPS recipient with clearly identified portal venules (stars) and diminishedparenchymal echogenicity (sky) that accentuates the portal venule walls.

TWIN RESEARCH AND HUMAN GENETICS 225

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sIUGR

• Point of difference from TTTS

“Even if FGR fetus has oligohydramnios <2cm; the AGA fetus will have less than 8cm DVP of amniotic fluid”

sIUGRType*

Features (>20 weeks gestation)

Type 1 EFW <10th; >25% EFW discordance; Normal UA

Type 2 EFW <10th; >25% EFW discordance; AREDF in UA

Type 3 EFW <10th; >25% EFW discordance; Cyclical intermittent AREDF in UA

*2007 Gratacos UOG

Single twin demise

If one twin demises:• 15% chance the other (i.e. both

twins) will die• Survivors have approximately 15 -

25% neurodevelopmental impairment risk

• 70% chance of preterm birth

• Blood pressure drops• Due to exsanguination to co-twin• Anemia/hypoxia/tissue damage

• FDIU àNo cardiac output• Feto-fetal transfusion ceases• Becomes “reservoir for other twin”

Management:• Immediate (24 to 48h after event)

surveillance for acute anemia• Rest of pregnancy surveillance for

intracranial insult

ISUOG Practice Guidelines: role of ultrasound in twin pregnancy

Ultrasound in Obstetrics & Gynecology, Volume: 47, Issue: 2, Pages: 247-263, First published: 18 November 2015, DOI: (10.1002/uog.15821)

11 -14 weeks

16 weeks

18 weeks

20 weeks

22 weeks

24 weeks

26 weeks

28 weeks

30 weeks

32 weeks

34 weeks

36 weeks

• Dating, labeling• Chorionicity• Screening for T21

• Fetal grow th, DVP• U A-PI

• Detailed anatom y• Fetal grow th, DVP• U A-PI, M CA-PSV• Cervical Length

• Fetal grow th, DVP• U A-PI, M CA-PSVM

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MC twin monitoring

For uncomplicated MC pregnancies:• One USS at T1 for anatomy• Fortnightly scans from 16 weeks for timely

detection of TTTS/TAPS • Improves perinatal outcomes

Deepest Vertical Pocket of Amniotic fluid to be done every scan for TTTS detection

From 20 weeks onwards: MCA PSV to be measured for TAPS screening

Cervical length assessment at 20 week scan

Conclusions• First trimester determination of chorionicity is of Primary

Importance• 1 in 3 monochorionic twins will develop TTTS; sIUGR or

TAPS• Frequent monitoring for early diagnosis of TTTS –

fortnightly from 16 weeks • Ultrasound parameters: DVP; Biometry; UA-PI, MCA-PSV,

DV-PI