Ultrasound Imaging in Multifetal Pregnancies: Its

“Ultrasound Imaging in 

Multifetal Pregnancies: 

Its More than Chorionicity” 

Anthony Johnson, DO 

Professor, UTHSC, Houston, TX 

Co-Director, Texas Fetal Center, CMHH 

1

Disclosures 

• I have no relationships with commercial companies 

that could be perceived as a conflict of interest. 

• I will not be discussing the use of products that are 

investigational or approved devices that are being 

used “off label”

Perinatal mortality 

MC vs. DC twins 

Dutch cohort study 1995-2004 

Outcome 

Perinatal 

Mortality 

MC 

(n = 198) 

DC 

(1107) 

Hazard Risk 

(95%CI) 

11.6% 5.0% 2.44 

(1.73-3.44) 

Stillbirth 7.6% 1.5% 5.21 

(3.18-8.51) 

Screening protocol: 

- 1 st trimester ultrasound for chorionicity 

- 20 wks anatomic survey 

- Serial ultrasounds (fortnightly) for growth, AFV and Doppler assessment 

Hack KEA et al BJOG 2008;115:58-67

Outcome of MCDA twin gestations in the 

era of invasive fetal therapy 

Survival 

Twin live births 172 85% 

Singleton 15 7% 

Double demise 15 7% 

Complication 

TTTS 18 9% 

sIUGR 30 15% 

Losses 

Total 11% (TTTS ~ 42%) 

< 24 weeks 84% 

> 24 weeks 16% 

> 32 weeks 1% 

Extra loss in MC twins is due to complications placental anastomoses 

Lewi et al., 2008

Complications in Monochorionic 

Multi-Fetal Pregnancies 

• Twin-Twin Transfusion Syndrome 

- Oligo/Polyhydramnios Sequence ~ TOPS 

- Twin Anemia Polycythemia Sequence ~ TAPS 

• Twin Reverse Arterial Perfusion 

• Growth Discordance 

• Discordant malformations 

- Structural 

- Chromosomal 

• Monoamnioitc

Diagnosis

"There is NO diagnosis of twins.” 

“The only diagnosis is a monochorionic or 

dichorionic twin gestation. 

This should be written in capital red letters 

on the front of the chart at 8 - 10 weeks". 

K Nicolaides, 02/27/09

Multifetal Pregnancies 

Ultrasound Determination of 

Amnionicity & Chorionicity 

1 st Trimester Ultrasound Examination: 

- Amnionicity and chorionicity should be documented for all 

multiple gestations when possible. 

2 nd & 3 rd Trimester Ultrasound Examination: 

- Multiple gestations require the documentation of additional 

information: chorionicity, amnionicity, comparison of fetal 

sizes, estimation of amniotic fluid volume on each side of 

the membrane, and fetal genitalia (when visualized). 

AIUM PRACTICE GUIDELINES, Oct 2007 

ACOG PRACTICE GUIDELINES, #101, Reaffirmed 2011

Ultrasound techniques for determining 

chorionicity & amnionicity 

Umbilical cord entanglement 

Fetal sex 

Separate placental discs 

No. of layers in membrane 

Membrane thickness 

Lambda or Twin Peaks or T-sign 

No. of yolk sacs 

No. of gestational sacs 

amnionicity 

chorionicity 

First trimester Second Trimester Third Trimester 

J Robinson & AZ Abuhamad Modern Medicine 2002

Multifetal Pregnancies 

Chorionicity 

Monochorionic 

“T” sign 

Dichorionic 

Lambda or Twin Peak sign 

Moise KJ Texas Medicine 2007

Multifetal Pregnancies ~ Establish chorionicity 

10 - 14 weeks 

“T” sign 

Monochorionic 

Twin Peak (lambda) 

Dichorionic

Accuracy of Ultrasonographic 

Chorionicity Classification* 

Pathologic Evaluation 

Misclassification 

Total 545 6.4% 

Dichorionic 455 4% 

Monochorionic 90 19% 

*Classified by ultrasound < 20 weeks 

Sensitivity Specificity PPV NPV 

96% 81% 96% 80% 

< 14 wks vs. 15-20 wks 

Odds Ratio: 0.47; 95% CI 0.23, 0.96 

58% ACOG optimal time for Dx chorionicity 1 st trimester 

62% Manage all twins without MFM consultation 

Blumenfeld Y AIUM 2013; Cleary-Goldman J et al 2004

Accuracy of referral vs. tertiary diagnosis of 

amnionicity and chorionicity 

Twins 

DADC 

DAMC 

MOMO 

Triplets 

TATC 

TADC 

TAMC 

Center DADC DAMC MOMO Total 

Referring 

Tertiary 


Tertiary 


Tertiary 


Tertiary 


Tertiary 


Tertiary 

45% 

98% 

28% 

96% 

49% 

96% 

24% 

92% 

50% 

83% 

0 

100% 

83 

167 

40 

72 

8 

5 

8 

25 

4 

13 

1 

1 

Accurate diagnosis of A/C can be obtained by assessment of key sonographic findings 

Emphasis on need to enhance diagnostic skills in the general community & referral if dx ambiguous 

Wan JJ et al Prenat Diagn 2011

Take home message 

Two is better than one !!

Bipartite Monochorionic 

Placentation 

• Twin Pregnancies with two 

separate placental masses can 

still be monochorionic and have 

vascular anastomoses 

• Lopriore E, et al 2006 ~ 3/109 

• Machin GA et al 2002 ~ 8/600 

If is looks like TTTS ~ it is until proven otherwise

Monozygotic Twins 

Incidence of Anomalies 

– 845 pairs of twins w/evaluation of zygosity: 

• 483 monozygotic 

• 252 dizygotic 

• 110 zygosity unconfirmed 

– Anomalies: 

• MZ: 2.7% (82% discordant) 

• DZ: 1% (100% discordant) 

• Singletons: 0.6% 

Chen et al. Acta Genet Med Gememol 1992;41:197-203

Bahityar MO, J Ultrasound Med 2007;26:1491

Monochorionic Twins 

Management of Anomalies 

Risk of death or longterm compromise co-twin 

• Old theory of “bad humors’ crossing to the live twin 

discounted 

• Acute hemodynamic changes the more likely etiology 

• No benefit from acute delivery 

• 15% of cases associated with IUFD of co-twin 

– ↑ 5X over dichorionic twins 

• 34% abnormal postnatal cranial imagine with IUFD co-twin 

• 26% of survivors with neurologic sequelae 

– ↑ 12X over dichorionic twins 

Fusi et al. Obstet Gynecol 1991;78:517-20 

Ong et al. BJOG 2006;113:992-8 

Hillman et al Obstet Gynecol 2011;118:928-40

Maternal-Fetal Surgery: Balancing Risks 

Discordant Fetal Malformation 

Multifetal Gestations 

Observation 

Intervention

Perinatal Outcomes of Twin Pregnancies 

Discordant for Major Fetal Anomalies 

Category Normal Twins Discordant 

Twins* 

Number 235 13 

GA_Delivery 34 

(16-40) 

Birth Weight 2030 

(180 – 3680) 


Survival 

*2/3 cotwin in MCDA set end as IUFD 

32 

(24-37) 

1640 

(520-3320) 

P 

0.029 

0.022 

91% 69% 0.018 

Gul A et al, Fetal Diagno Ther 2005;20:244

Dilemmas in Management of twins discordant 

for anencephaly diagnosed at 11-14 weeks 

Chorionicity # Hydramnios Livebirth GA 

Delivery 

Delivery 

< 33 wks 

DICHORIONIC 

Expectant Obs 

Reduction 

35 

9 

57% 

0 

97% 

89% 

36 

37 

18% 

13% 

Monochorionic 

Expectant Obs 19 52% 84%* 33 38% 

MC Intervention 

Laser coagulation 

Cord Ligation 

Bipolar 

6 

24 

92 

100% 

54% 

77% 

33% 

69% 

31% 

* IUFD of affected Twin with co-twin demise in 3/4 

Vandecruys H Ultrasound Obstet Gynecol 2006;28:653

Acardiac Twin 

Incidence 1/35,000 

Earliest form of TTTS 

Reverse Arterial Perfusion ~‘acardiac” 

Co-twin anomaly ~ 10% 

Perinatal M&M ~ 50% 

Growth AT:PUMP 70% 

Polyhydramnios 

Cardiac decompensation in pump twin

Acardiac Twin

Acardiac Twin

Outcome in TRAP Pregnancies 

Observation vs. Intervention 

Acardiac size < 50% of Pump 

Group N Acardiac 

Size 

MOMO 

Pump 

Survival 

GA 

Delivery 

Observation 8 27% 38% 88% 34 

Intervention 

(RFA) 

7 49% 0% 100% 36 

Jelin E et al Fetal Diagn Therp 2010:27;138

Outcome of TRAP sequence diagnosed in the 

IUFD of 

pump twin, 33% 

first trimester 

Survival Rate 

1 st Tri DX 

46% 11/24 

Arrest of Flow 

Acardiac, 24% 

3/5 Pump twins 

Demise or Abnl CNS 

Following arrest 

of flow to acardiac 

Pump alive Flow 

In Acardiac, 46% 

Intervention need 

12-16 weeks 

Liesbeth L et al, AJOG, 2010; 203,213.e1 - 213.e4

Twin-twin 

Transfusion 

Syndrome


Epidemiology of TTTS 

• Complicates 9 – 15% of MCDA twins 

• 1 in 58 twin pregnancies 

• 1 in 4,170 pregnancies 

• Presentation < 26 weeks ~ 90% perinatal mortality 

Dickinson et al. Am J Obstet Gynecol 2000;182:706-12 

Saunders et al. Am J Obstet Gynecol 1992;166:820-4

Twin Twin Transfusion 

Syndrome Diagnosis 

Single placenta 

Polyhydramnios (8cm) / oligohydramnios (2cm) 

Concordant for sex 

Discordant for size and placental echogenicity 

Recipient persistent enlarged bladder 

Donor small or non-visible bladder

Prediction of Twin Twin Transfusion 

Nuchal Translucency 

Folding Intertwin Membrane 

Arterio-arterial anastomoses 

Discordant AFV* 

*Sueters M et al Ultrasound Obstet Gynecol. 2006 Oct;28(5):659-64

Twin-Twin Transfusion Syndrome Staging 

(TOPS) 

Stage I 

Stage II 

Stage III 

Stage IV 

Oligohydramnios(8cm) 

Discordant fluid volume 

No bladder in the donor twin 

Doppler flow- absent or reversed in umbilical artery or 

ductus venosus, pulsatile flow in the umbilical vein 

Hydrops in one or both fetuses 

Stage V 

One or both fetuses have died 

Quintero R et al J. Perinatol 1999;19:55

Quintero Stage Related Outcomes in TTT 

Following Laser Photocoagulation 

Report N I II III IV 

Quintero, 2003 

Both 

95 

67% 

49% 

25% 

46% 

> 1 

86% 

86% 

79% 

82% 

Huber, 2006 

Both 

200 

76% 

61% 

54% 

50% 

> 1 

93% 

83% 

83% 

70%

Suspected TTTS 

How often Dx Correct & Referral Timely 

N % 

Confirmed Dx TTTS 249 77% 

Stage 

1 

2 

3 

4 

5 

28 

50 

150 

15 

10 

11% 

20% 

60% 

6% 

4% 

No TTTS 75 23% 

Discordant AFV 

sIUGR 

42 

33 

56% 

44% 

Gandhi M et al, 2012

Twin Anemia-Polycythemia Sequence 

(TAPS) 

• Larger intertwin hemoglobin difference w/o signs of 

TOPS 

• Intertwin blood transfusion w/o hormonal 

imbalance 

• Post laser: ex-recipient anemic w/ ex-donor 

polycythemic ~ 77% 

• Spontaneous reported as early as 16 weeks 

Study N Post-laser 

Robyr, 2006 101 13% 

Habli, 2009 152 2% 

Slagehekke,2010 276 8% 

Spontaneous* 

Lewi et al, 2009 202 5% 

Lopriore, 2010 113 5% 

Slagehekke F et al Fetal Diagn Therapy 2010

TAPS 

Optimal Management is Unclear 

• Expectant observation 

• Induction of labor 

• Selective reduction 

• Laser photocoagulation 

• Intrauterine transfusion 

Intravascular/intraperitoneal 

IV / exchange transfusion 

• Perinatal mortality and 

morbidity unknown 

• Majority Dual Survivors 

• IUFD (dual & single) 

• Thrombosis, CNS 

Infarct; Hydrops 

Delivery 32 wks 4 days 

Dual survivors 

Single AA at placental edge 

Herway C et al Ultrasound Obstet Gynecol 2009;33:592

Vascular Occlusion Injuries in TTTS 

• 95% recipient 

• 85% lower limb 

• 71% right sided 

• Intestinal atresia 

• Mechanism 

• Polycythemia 

• Hyperviscosity 

• Hypertension 

• Vascoconstriction 

Schrey S et al AJOG 2012

Discordant Growth & Selective IUGR

Discordant Growth in Twin Pregnancies 

Associated Outcomes 

• Anomalies 

• IUGR 

• Preterm Birth 

• Intrauterine infection 

• Stillbirth 

• UA cord ph < 7.10 

• NICU Admission 

• RDS 

• Neonatal Death 

Debate 

• Detection efficacy 

• Significant threshold 

• Co-morbidities 

• Management strategy 

ACOG Practice Bulletin #56, reaffirmed 2009

Factors Affecting Fetal 

Maternal 

Placental* 

Fetal 

Growth Discordance 

• Tobacco 

• Vascular disease 

• Poor prenatal care 

• Low Maternal wt gain 

• Vascular anastomoses 

• Placental sharing 

• Placental weight 

• Velamentous insertion 

• Aneuploidy 

• Sex-discordance 

• Viral Infection 

* Major component of discordance in MC twinning

Definition & Impact of Discordant 

Fetal Growth in MC Twins 

Discordant growth = selective growth restriction 

• Discordant Growth 

- (Largest – Smallest) / Largest * 100 

- EFW or birthweight 

- ACOG defines discordance 15-25% 

- SOGC – > 20% EFW or [AC large – AC small] > 20 mm 

31 publications > 1.1 million twins 

16% discordance 

137,000 US twin births/yr 

22,000 discordant twins/yr 

Martin JA CDC NCHS data brief 80;2012 

Miller J et al AJOG 2012:206;10

First trimester prediction 

Twin complications & adverse outcome 

Study # Placenta Bwt 

> 20% 

sIUGR 

Early 

IUFD 


Mortality 

Sebire, 1998 549 MC/DC - - + - 

Kalish, 2004 159 DC + - + - 

Tai, 2007 178 MC/DC + - - - 

Banks, 2008 135 DC - - - - 

Memmo, 2011 242 MC + 

D’Antonio, 2013 2155 MC/DC - - - - 

In the absence of aneuploidy or structural malformations CRL discordance 

is a poor predictor for adverse perinatal outcome in MC and DC twin pregnancies 

D’Antonio F, Ultrasound Obstet Gynecol.2013; Feb 14. doi: 10.1002/uog.12430

Discordant Growth in Twin Pregnancies 

2 nd Trimester Ultrasound Predictive Accuracy 

Discordance > 20% 

Screening Test Sensitivity Specificity 

AC 65-83% 65-90% 

EFW 50-93% 80-93% 

Miller J et al AJOG. 2012;206:10-20

Discordance & Adverse Outcome by Chorionicity 

DC 18% discordance = 

Uncomplicated MC 

MC 18% discordance 

double risk of adverse outcome 

SGA 5% 

18% BW 

Discordance 

Choriionicity HR (95% CI) P HR (95% CI) P 

Monochorionic 2.6 (1.4-4.7)

Clinical 

MCDA Discordant Growth* 

Early 

(15) 

Late 

(13) 

Discordance EFW > 20% < 20 wks > 26 wks 

Concordant 

(150) 

UA Doppler abnl 73% 0 3% 

IUFD 27% 8% 1% 

TAPS 0 38% 3% 

GA_Delivery 33 35 35 

Birthwt discordance 30% 31% 9% 

Overall Survival Rate 83% 96% 99% 

Placenta 

Placenta Territory ratio 2.55 1.6 1.4 

Total Anastomotic 

Diameter (mm) 

* Bwt Discordance > 25% 

14 6 9 

Lewi L AJOG 2008;199:511.e1


Selective IUGR 

• 10-15% of monochorionic twins 

• Smaller twin EFW < 10%tile for gestational age 

• Unequal placental sharing 

• +/- Unbalanced intertwin vascular flow 

• Perinatal mortality & long term morbidity 

- Smaller twin: IUFD 30-40% Neurologic 15-40% 

- Cotwin twin: IUFD 25-30% Neurologic 20-30% 

- iatrogenic prematurity 

- acute feto-feto transfusion


Classification sIUGR 

Type 

Umbilical 

Artery 

IUFD 

Neurologic 

Compromise 

In Utero 

Deterioration 

GA 

Delivery 

I Normal 2-4%

Perinatal outcome with expectant observation in 

sIUGR by Umbilical Artery Doppler Classification 

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0 

96% 

2% 

2% 

33% 

26% 

41% 

38% 

23% 

38% 

Intact 

Survivors 

Both 

One 

None 

Type I Type II Type III 

(23) (27) (13) 

Ishii K et al Fetal Diagn Ther 2009;26:157


Selective IUGR 

Expectant Observation 

• Fetal monitoring 

- Biophysical profile 

- Ductus venosus Doppler blood flow studies in Type II 

• Early delivery 

• Selective reduction 

• Laser ablation placental anastomoses ~ RCT

Monochorionic Diamniotic Twins 

Frequency of Ultrasound Evaluations 

• Serial sonographic evaluations every 2 weeks, beginning at 

16 weeks, until delivery, should be considered for all twins 

with MCDA placentation 

• Screening for congenital heart disease is warranted in all 

MC twins, in particular those complicated with TTTS 

SMFM Committee Opinion 

Am J Obstet Gynecol. 2013;208(1):3-18

Two Step Screening Strategy for 

Complicated Outcomes in MC Twins 

Lewi L et al Am J Obstet Gynecol 2008;199:511.e1-7

Twins Ultrasound Surveillance 

All twins 

- Ultrasound for anomalies at 18 – 20 weeks 

- Placental Cord Insertions 

- Weekly Biophysical profile > 32 weeks 

Dichorionic 

- Ultrasounds Q 4 weeks for serial growth 

- Change in AFV and Doppler UA may precede discordant growth 

Monochorionic twins 

- Ultrasounds alternate limited and growth, Q 2 weeks, 16 wks 

- Amniotic fluid volume, bladder 

- Fetal growth 

- Doppler blood flow studies 

- UA, UV, DV and MCA baseline 20 weeks 

- Repeat if > 20% discordance with smaller < 10% 

- Uncomplicated or late discordance MCA 

- Fetal echocardiography

Conclusion 

Increase awareness of risks associated with MC pregnancies by 

healthcare providers and patients 

– “No Dx Twins” 

• Establish chorionicity early 

• Risk stratify multifetal pregnancies DC vs. MC 

– MC pregnancies serial ultrasound beginning at 16 weeks 

• Limited (MVP, UA and bladder) 

• Growth studies with Doppler assessment 

– MFM/Fetal Treatment Center referral consultation for 

• Targeted ultrasound/echo 

• Signs of discordance growth or AFV 

Update ACOG Practice Bulletin #56 October, Multiple Gestation: 

Complicated Twins, Triplets and High-Order Multifetal Pregnancy 

5 

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Ultrasound Imaging in Multifetal Pregnancies: Its

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