Fetal surveillance in twin pregnancies is important due to increased risks of complications. Ultrasound is used to determine chorionicity and amnionicity, monitor growth, check for anomalies, and screen for conditions unique to twins like twin-twin transfusion syndrome. Dichorionic twins are monitored every 4 weeks after 16 weeks while monochorionic twins are monitored every 2 weeks due to higher risks. Complications require specialized management and timely intervention can help reduce poor outcomes for twins.

1. FETAL SURVEILLANCE IN TWIN
PREGNANCY
Dr. Alka Pandey
MD, Ph.D.

2. • Presence of more than one fetus in the gravid uterus

3. TYPES OF TWIN PREGNANCY
Monozygotic Dizygotic

4. MONOZYGOTIC TWINS
•Not affected by heredity.
•Not related to induction of ovulation.
•Constitutes 1/3 of twins.

5. DIZYGOTIC TWINS/ BINOVULAR
•Fertilisation of 2 ova by different
spermatozoa.
•Each twin has its own placenta,
chorion, amnion.
•Hence always dichorionic,
diamniotic.

6. Incidence
• Incidence - 1-3% of all pregnancies
• Incidence of monochorionic twin pregnancy is 1:250 which is fixed.
Incidence of dichorionic twin pregnancy is increasing

7. • ZYGOSITY : -
- Refers to the Type of Conception.
- only determined by DNA testing
• CHORIONICITY : -
- Type of Placentation
- Determined:
- prenatally by ultrasound
- postnatally by examining membranes.
- Ideal time for assesment is before 14 weeks

8. Which is more important – Zygosity or
Chorionicity??

9. CHORIONICITY………Why????•
• Dichorionic twins can be either mono/dizygotic.
• Dichorionic twins develop as two distinct organs. – so less risk.

10. CHORIONICITY………Why????•
• Monochorionic twins have increased vascular anastomoses between
the two circulation – so high risk!!

11. Ultrasound Determination of Chorionicity

12. • Twin peak / Lambda sign –
- characteristic of Dichorionic
pregnancies
- chorionic tissue between 2 layers
of intertwin membrane at the
placental origin
• T Sign – in monochorionic ,
There is no chorionic tissue
Ultrasound Determination of Chorionicity

13. Fetal Complications
• Twin pregnancy is associated with High Risk of Perinatal mortality and
morbidity.
• Congenital anomalies.
• Preterm birth – Prior to 37 weeks – 60 %
• IUGR
• Cord prolapse
• Locked twins

14. Risks are significantly higher in monochorionic compared
with dichorionic pregnancy.
• Twin to Twin transfusion
syndrome
• TRAP (Twin reversed
arterial perfusion)
• Single fetal demise.
• TAPS – Twin anaemia –
Polycythemia sequence

15. Twin pregnancy is associated with high risk of
perinatal morbidity and mortality
hence
surveillance is of paramount importance

16. Surveillance includes
• Dating of the pregnancy
• Determining chorionicity and amnionicity.
• Twin labeling
• Timing, frequency and content of ultrasound assessment.
• Screening for aneuploidy.
• Prenatal diagnosis of aneuploidy.

17. • Screening for structural abnormalities.
• Diagnosis and management of discordant twin pregnancy.
• Fetal reduction/selective termination.
• Screening for preterm birth.
• Screening, diagnosis and management of FGR.
• Management of multiple pregnancy complicated by single IUD.

18. Complications unique to monochorionic twin pregnancy.
- Screening diagnosis and management of TTTS
- Screening, diagnosis and management of TAPS
- Screening & management of TRAP sequence.
- Screening & management of monochorionic monamniotic (MCMA)
twin pregnancy.
- Diagnosis and management of conjoined twins.

19. Dating of Twin Pregnancy
Twin pregnancies should ideally be dated when the crown-rump
length measurement is between 45 and 84 mm (i.e. 11+0 to 13+6
weeks of gestation).
In pregnancy conceived spontaneously, the larger of the two CRLs
should be used to estimate gestational age.

20. Determining chorionicity/amnionicity in twin pregnancy
 Chorionicity should be determined before 13+6 weeks of gestation
 Using the membrane thickness at the site of insertion of the amniotic
membrane into the placenta
 Identifying the T sign or lambda sign, and the number of placental
masses.

21. Determining chorionicity/amnionicity in twin pregnancy
 It is important to examine the dividing membrane carefully;
 In dichorionic diamniotic twin pregnancy, the twins are
separated by a thick layer of fused chorionic membrane with
two thin amniotic layers, one on each side, giving the
appearance of a ‘full lambda’,
 Compared with only two thin amniotic layers separating the
two fetuses in monochorionic diamniotic twin pregnancy.

22. Determining chorionicity/amnionicity in twin pregnancy
 An ultrasound image demonstrating the chorionicity should be kept in the
records for future reference.
 At the time at which chorionicity is determined, amnionicity should also be
determined and documented.

23. Determining chorionicity/amnionicity in twin pregnancy
 Cord entanglement should be looked for.
 It is almost universal in MCMA twin pregnancy,
 Using pulsed-wave Doppler, two distinct arterial waveform patterns with
different heart rates are seen.

24. Labeling of twin fetuses
•The labeling of twin fetuses should
follow a reliable and consistent strategy
and should be documented.
• It is advisable to describe each twin
using as many features as possible so as
to enable others to identify them
accurately.
• It should be borne in mind that the
twins labeled as ‘Twin A’ and ‘Twin B’
during antenatal ultrasound scans may
not necessarily be delivered in that
order.

25. Routine monitoring of twin pregnancy with ultrasound
• Women with an uncomplicated dichorionic twin pregnancy should have a first-
trimester scan, dating, labeling, chorionicity and screening for trisomy 21.
• Detailed second-trimester scan at 16 weeks, detailed anatomy, biometry, AFV
and cervical length.
• Scans every 4 weeks thereafter for assessment of fetal growth, AFV and Fetal
Doppler.
• Complicated dichorionic twins should be scanned more frequently, depending on
the condition and its severity.

26. Routine monitoring of twin pregnancy with ultrasound
• Uncomplicated monochorionic twins should have a first-trimester and second-
trimester scan and be scanned every 2 weeks after 16 weeks in order to detect
TTS and TAPS in a timely manner.
• Complicated monochorionic twins should be scanned more frequently,
depending on the condition and its severity.

27. Screening for chromosomal abnormalities in twin pregnancy
• Screening for trisomy 21 can be performed in the first trimester using the
combined test (nuchal translucency thickness (NT), free beta-human chorionic
gonadotropin (-hCG) level and pregnancy-associated plasma protein-A (PAPP-A)
level).
• An alternative is combination of maternal age and NT only.
• The detection rate of non-invasive prenatal testing for trisomy 21 may be lower in
twins than in singletons.

28. Invasive prenatal diagnosis in twin pregnancy
• CVS is preferred in dichorionic twin pregnancy. It can be performed earlier than
amniocentesis.
• Earlier diagnosis of any aneuploidy is particularly important as carries a lower risk
of selective termination in the first compared with the second trimester.
• If monochorionicity has been confirmed before 14 weeks’ gestation and the
fetuses appear concordant for growth and anatomy, it is acceptable to sample only
one amniotic sac.

29. Implications of discordance in NT or CRL in the first trimester
• The management of twin pregnancy with CRL discordance 10% or of NT discordance 
20% should be discussed with a fetal medicine expert.
• Discordance in NT of  20% is found in around 25% of monochorionic twins and the risk
of early IUD or development of severe TTTS in this group is more than 30%.
• Discordance in CRL at 11-13 weeks gestation is significantly associated with pregnancy
loss.

30. Ultrasound screening for structural abnormalities in
twin pregnancy
* Twin fetuses should be assessed for the presence any major
anomalies at the first-trimester scan, and a routine second-trimester
(anomaly) scan should be performed at around 20 (18-22) weeks’
gestation.
* Cardiac screening assessment should be performed in
monochorionic twins.
* Twin pregnancies discordant for fetal anomaly should be referred
to a fetal medicine center.
In dichorionic twin pregnancy, selective feticide is performed by ultrasound guided intracardiac or
intrafunicular injection of potassium chloride or lignocaine, perferably in the first trimester.
In monochorionic twins selective feticide is performed by cord occlusion, laser ablation or
radiofrequency ablation.

31. Screening for risk of preterm birth in twin pregnancy
 Cervical length measurement is the preferred method of screening for preterm birth in
twins; 25mm is the cut-off most commonly used in the second trimester.

32. Screening diagnosis and management of fetal growth restriction
 sFGR, conventionally, is defined as a condition in which one fetus has EFW <10th centile and
the intertwin EFW discordance is >25%.
 A combination of head, abdomen and femur measurement performs best in calculating EFW.
 After diagnosis a detailed anomaly scan and screening for viral infections (cytomegalovirus,
rubella and toxoplasmosis.
 Amniocentesis may also be required to exclude chromosomal abnormalities as a cause of
FGR.
 sFGR in monochorionic twin pregnancy occurs mainly due to unequal sharing of the placental
mass and vasculature.
 If discordance is >25% referral should be made to tertiary fetal medicine unit.

33. Classification of sFGR in monochorionic twins.
This depends on the pattern of end-diastolic velocity in the umbilical artery.
 Type I - the umbilical artery Doppler waveform has positive end-diastolic flow.
 Type II- there is absent or reversed end-diastolic flow.
 Type III – there is a cyclical/intermittent pattern of AREDF.
 In dichorionic twin pregnancy complicated by sFGR, fetal Doppler should be assessed
approximately every 2 weeks.
 In monochorionic twin pregnancy complicated by sFGR, fetal Doppler should be
assessed at least weekly.
 Monitoring for progressive deterioration of umbilical artery, MCA and DV Doppler, and
of biophysical profile scores.

34. Managing the surviving twin after demise of its cotwin
 In monochorionic twin pregnancy, assessment of fetal Doppler, especially MCA-
PSV, in order to look for sign of fetal anemia in the surviving twin should be done.
 In preterm, prolonging the pregnancy for the benefit of the surviving twin is
recommended.
 Detailed counseling about significant morbidity of the parents is required.

35. Managing the surviving twin after demise of its cotwin
 The surviving twin should be assessed by CTG, umbilical and MCA Doppler
biometry.
 Delivery should be considered of at 34-36 weeks .
 Fetal brain should be imaged around 4-6 weeks after the death of the cotwin to
search for evidence of cerebral morbidity.
 Neuro developmental assessment of the surviving twin at the age of 2 years should
be recommended.

36. Complications unique to monochorionic
twin pregnancy – TTTS
 TTS affects 10-15% of monochorionic twin
pregnancies and is associated with increased
perinatal mortality and morbidity.
 In monochorionic twin pregnancy, screening for
TTTS should start at 16 weeks, with scans repeated
every 2 weeks thereafter.

37. Stage Classification
I Polyhydramnios-oligohydramnios sequence:
DVP >8cm in recipient twin and DVP <2cm in donor twin
II Bladder in donor twin not visible on ultrasound
III Absent or reversed umbilical artery diastolic flow, reversed ductus venosus a-wave flow, pulsatile
umbilical venous flow in either twin
IV Hydrops in one or both twins
V Death of one or both twins
Treatment may be conservative, lesser ablation or serial amnioreduction according to situation.

39. Screening diagnosis and management of twin anemia-polycythemia
sequence (TAPS)
 The prenatal diagnosis of TAPS is based on the finding of discordant MCA Doppler
abnormalities.
 There is little evidence about the outcome and optimal management of TAPS;
therefore treatment options should be individualized and discussed with parents.

40. Twin reversed arterial perfusion (TRAP) sequence
TRAP sequence pregnancies are usually monitored serially, with the aim of undertaking
intrauterine therapy if cardiac strain becomes evident in the pump twin or there is
increased perfusion and growth of the TRAP mass.
 However, close monitoring with ultrasound and Doppler does not prevent sudden
demise.

41. Monochorionic monoamniotic (MCMA) twins
Umbilical cord entranglement is almost always present in MCMA twins .
 Delivery by Cesarean section is recommended at 32-34 weeks.

42. Conjoined Twins
Conjoined twins are always MCMA twin pregnancies.
 Diagnosis with ultrasound in the first trimester is now the norm.
 Usually termination is done in the first trimester .
 If undiagnosed there is significant risk of obstructed labour, dystocia
and uterine rupture , so delivery by elective Caesarean section should be
done.

43. Monitoring of twins in labour
• All twins must have an ultrasound scan to establish the position of
both fetal hearts prior to attaching the CTG monitor.
• A diagram should be made in the notes of the CTG indicating which
fetus is being monitored by the transducer.
• CEFM of both twins should be done in active labour.

44. Summary
• Chorionicity should be established before 14 weeks.
• Ultrasound monitoring in Dichorionic twin pregnancy should be done
every 4 weeks starting from 16 weeks.
• Ultrasound monitoring in Monochorionic twin pregnancy should be
done every 15 days starting from 16 weeks.
• Proper and timely screening for TTTS, TAPS, TRAP, Single Fetal
Demise, Congenital Fetal Abnormalities, Cord entanglement may help
to save many fetal lives.