ULTRASOUND IN TWIN PREGNANCY.pptx

ULTRASOUND IN
TWIN PREGNANCY
PRESENTED BY – DR. ANKITA
MODERATED BY – DR. VINAYA POORNIMA

DATING
• Dating using CRL prior to 14 weeks is the standard practice
• Multiple fetuses are rarely identical in size
• We can choose the largest , the smallest or the mean of the two CRLs to date
the pregnancy
• Smaller CRL = most reflective of true gestational age
- risk of assuming that the larger twin is ‘large for dates’
- failure to diagnose a growth restricted small twin.

DATING
• Mean of the two CRL measurements may be used to date the pregnancy
- associated with underestimation.
• Most common choice is to use the larger CRL for dating
- slight overestimation of gestational age
- protects against the misdiagnosis of IUGR in the small twin
• If via IVF – gestational age calculated using the date of embryo transfer.

• Twin pregnancies can be monozygotic or dizygotic
 Dizygotic – 2 separate fertilizations
 Monozygotic – single fertilization

• All twin pregnancies have a higher risk of :
Preterm labor
Maternal hypertensive disorders
Maternal diabetes
Premature rupture of membranes
• Chorionicity determines the prognosis.

Establishing Chorionicity
• Most accurate in 1st trimester – 98% accurate.

Chorionicity and Amnionicity in 1st Trimester
• Gestational sac is created by the chorion.
• Hence , number of gestational sacs = chorionicity of the pregnancy.
• DC pregnancy – 2 gestational sacs present
• MC pregnancy – single gestational sac created by a single rim of chorionic
tissue.

• Upto 7-9 weeks post-fertilization , amnion may not be detectable.
• Amnionicity may be suggested by the number of yolk sacs.
 2 yolk sacs – s/o DA twins
 1 yolk sac – s/o MA twins
• However , verification at follow up USG is required.

• Chorion is the precursor of placenta.
• At 10-14 weeks gestation , placenta becomes a distinct structure.
• Hence number of placental masses = chorionicity.
• Thick membrane composed of 2 chorions and 2 amnions is depicted
between DC twins
• Thin membrane composed of only 2 layers of amnion is depicted between
MC twins.

• In DC twins , chorionic tissue extending from the placenta into the base of
the thick membrane creates the “ twin peak sign”.
• In MCDA twins , the amnions abut the placenta without intervening
chorion, creating the “ T sign”
• In MCMA twins , both embryos are in a common space surrounded by a
single chorion and a single amnion.

Chorionicity and Amnionicity in 2nd and 3rd
Trimesters
• Number of placental masses
• Thickness of the membrane
• Twin peak sign
• Fetal sex
• Cord entanglement : hallmark of MA pregnancy
• Conjoined twins: only in MA pregnancy.

TWIN LABELLING
• Begins at first scan.
• Should be consistent at every subsequent scan.
• Good practice to describe each twin as fully as possible.
• Each fetus needs to be uniquely identified and referred to as fetus A and fetus
B.

TWIN LABELLING
• Presence of unequal growth or unique anomalies confirms fetal identity.
• In the absence of such discriminating features , placental cord insertions
are best used to identify the fetuses.
• By convention , the presenting twin is twin A.

SCREENING FOR FETAL STRUCTURAL
ABNOMLATIES IN TWINS
1.Anomaly screening in twins:
• Risk of fetal anomaly is greater than singleton pregnancies
• Scans are more technically demanding
• Skilled operator should perform these scans
• Additional time should be given to adequately assess all fetal anatomy.

2. Discordant anomalies in twin pregnancies:
• Around 1 in 25 DCDA and 1 in 15 MCDA twin pairs will be affected by
major congenital anomaly , usually affecting only 1 twin.
• Cardiac anomalies are more common in MC pregnancies.
• Management is complicated – determined by the expected prognosis for the
affected twin and chorionicity.

2. Discordant anomalies in twin pregnancies: (contd)
• When intrauterine demise of the affected twin is anticipated in-
- DC pregnancies: expectant management and delivery of surviving co-twin is
appropriate.
- MC pregnancies: demise of one twin is followed by neurological injury or death of
unaffected co-twin. Hence , selective feticide of the affected twin may be preferable.

3. Use of 2nd trimester uterine artery doppler:
• Pre-eclampsia is one of the most common causes of maternal and fetal
mortality and morbidity.
• Even more common in twin pregnancies
• Doppler waveforms measured at 20-22 weeks predictive of pre-eclampsia.
• Uterine artery pulsatility index (UAPI) is lower in twin pregnancies with little
difference between MC and DC pregnancies.

4. Assessment of fetal growth in twins :
• Growth velocity of twins is lesser than in singletons in third trimester
• This is more pronounced and noted earlier in MC pregnancies.
• Need to identify if difference in observed growth represents adaptation or true restriction.
• EFW calculations are less accurate in twin pregnancies.
• Twin specific growth charts are more accurate.
• Doppler study may help in accurately identifying fetuses with growth limitation due to
placental insufficiency.

5. Size discordance in twins:
• Significant growth discrepancies in twins are associated with poor perinatal
outcomes.
• A growth discrepancy of >25% predicts poor perinatal outcome in twins.
• Discrepancy of 20-25% - refer to fetal medicine experts / additional
monitoring.

• Decision to deliver in DC pregnancies in very preterm pregnancies is
complicated as the normally growing twin may be iatrogenically
compromised by prematurity.

6. Frequency of growth assessment in twin pregnancies:
• Most international bodies recommend scanning of MC pregnancies every 2
weeks.
• Routine examination of DCDA twins is recommended every 4/4-6 weeks.
• Additional screening will lead to additional iatrogenic deliveries of babies
suspected to be compromised which will affect the mother as well as any
healthy co-twin.

COMPLICATIONS OF
MONOCHORNIONIC TWINNING
• Multiple vascular connections in the single shared placenta result in unique issues
complicating MC twin pregnancies. These include :
1. TTTS : a volume imbalance between the twins leads to progressive hypoxia in one
twin and severe volume overload in the recipient.
2. sFGR : one twin is significantly smaller than expected for gestational age.
3. TAPS : hemoglobin discrepancy between the twins without a volume difference
4. TRAP : an acardiac twin exists dependent on collateral circulation from the normal
‘pump’ twin.

COMPLICATIONS OF
MONOCHORNIONIC TWINNING
• The possible vascular connections are:
- arterio-arterial
- arterio-venous
- veno-venous.
• Neither arterio-venous nor veno-venous connections are readily demonstrable at
USG.
• With a diligent search, arterio-arterial anastomoses can be visualized in some cases.
• Arterio-arterial connections are thought to protect against the development of
TTTS

TWIN-TWIN TRANSFUSION SYNDROME
• TTTS is one of the most serious consequences of the anomalous
connections in the shared MC placenta.
• It affects 10%–15% of MC pregnancies but causes more than half of deaths
in MC-DA twins.
• If left untreated, pregnancy loss rates are as high as 70%–100%.
• Even surviving infants have a 10%–30% chance of neurologic morbidity.

PATHOGENESIS OF TTTS
• Vasoactive substances are thought to play a role.
• Unidirectional flow through a dominant arterio-venous anastomosis makes
one twin the donor and the other the recipient.
• Eventually, both fetuses develop progressive cardiovascular decompensation.
• In particular, increased afterload in the recipient causes myocardial
hypertrophy with abnormal diastolic and systolic function.

DIAGNOSIS OF TTTS
• The diagnosis of TTTS is usually made in the second trimester.
• The hallmark observation is oligohydramnios in one sac and polyhydramnios
in the other
• Once diagnosed, TTTS is staged based on imaging findings, with the
Quintero staging system.

STAGE 1
Oligohydramnios-Polyhydramnios Appearance
• Oligohydramnios effects the donor, with the maximum vertical pocket measuring
less than 2 cm
• Polyhydramnios affects the recipient twin, with the maximum vertical pocket
measuring greater than 8 cm
• Normal donor bladder is present.
• The diagnosis is much harder to make in MCMA twins, as there is only one
amniotic space. TTTS usually manifests with polyhydramnios in these patients.

STAGE 2
Absent Bladder
• In addition to the combination of oligohydramnios and polyhydramnios, the
donor bladder is absent in stage 2 TTTS .
• Usually, this is associated with anhydramnios, which creates the stuck twin
appearance.
• With no substantial amniotic fluid remaining in the sac, the donor twin is
shrink-wrapped in the membranes and becomes apposed to the uterine wall.

STAGE 3
Doppler Abnormalities:
• In cases of more severe disease, Doppler abnormalities become evident,
including absent diastolic flow in the umbilical artery , most commonly in the
donor twin.
• Reversed flow in the ductus venosus can also be depicted.
• Umbilical vein notching can be depicted, which is a premorbid waveform

STAGE 4
Hydrops Affecting One or Both Fetuses
• Hydrops is signified by the presence of fluid in two body compartments.
• Includes :
- body wall edema
- pleural effusion
- large pericardial effusion
- ascites

STAGE 5
Fetal Demise
• Single or dual twin demise may occur as a result of TTTS.

MANAGEMENT OF TTTS
• Expectant management with close surveillance- stage 1 TTTS.
• With expectant management, nearly three-fourths of pregnancies remain
stable, and most have survival of at least one twin.

MANAGEMENT OF TTTS
• Fetoscopic laser ablation is the most accepted treatment of TTTS.
• The goal is dichorionization of the placenta by laser ablation of abnormal
vascular anastomoses.
• It is a relatively safe procedure, but premature rupture of membranes occurs
in up to 30% of cases, especially with early gestational age at intervention.

MANAGEMENT OF TTTS
• Selective feticide is another option for managing TTTS.
• Usually by means of radiofrequency ablation.
• Reserved for conditions in which :
-one of the co-twins has discordant (potentially lethal) congenital anomalies.
-severe intrauterine growth restriction affects either of the twins.
- one of the twins is moribund.

TWIN ANEMIA POLYCYTHEMIA
SEQUENCE
• TAPS is a consequence of chronic unbalanced flow between the twins.
• Like TTTS, it is characterized by anemia of the donor twin and polycythemia
of the recipient twin.
• It occurs spontaneously in 3%–5% of MC twins after 26 weeks gestation and
in approximately 13% of cases treated with fetoscopic laser ablation for
TTTS because of incomplete dichorionization.

PATHOGENESIS OF TAPS
• Thought to result from submillimeter-caliber unidirectional arterio-venous
connections.
• Usually located close to the placental edges.
• Lack of arterio-arterial connections is believed to further accentuate this
condition

DIAGNOSIS OF TAPS
• Doppler US allows for a noninvasive US diagnosis of fetal anemia and
polycythemia by measuring MCA PSV.
• TAPS is diagnosed when the MCA PSV of one twin is greater than 1.5
multiples of the median (MoM), indicating anemia, and the MCA PSV of the
second twin is less than 1.0 MoM, indicating polycythemia.
• Online calculators can be used to calculate the MoM corresponding to
measured spectral Doppler US velocity.

MANAGEMENT OF TAPS
• The management of TAPS is still evolving.
• Depending on gestational age and fetal comorbidities, options include:
- expectant management
- selective feticide
- delivery
- intrauterine transfusion with/without partial exchange transfusion for the
polycythemic fetus
- fetoscopic laser photocoagulation

POLYHYDRAMNIOS AFFECTING
RECIPIENT-LIKE TWIN
• PART is a condition in which isolated polyhydramnios affects one twin of
the MC-DA pair, with normal fluid in the co-twin.
• Polyhydramnios is likely due to polyuria. However, there is no true donor, as
the co-twin has normal fluid.
• The bladder and Doppler US findings are normal.

PART
• Recent studies have shown that PART goes hand in hand with weight
discordance, and the fluid discordance is likely related to discrepant fetal
weights.
• Less than 25% of patients with PART progress to TTTS, and the overall
prognosis is good.
• The presence of arterial-arterial anastomosis is protective against
progression to more severe disease

TWIN REVERSED ARTERIAL
PERFUSION SEQUENCE
• Previously referred to as acardiac twinning.
• Rare complication specific to MC twin pregnancies.
• It occurs in about 1% of MC twins, mostly in MC-DA twins, but it can also
occur any multigestational pregnancy that includes an MC pair.

PATHOGENESIS OF TRAP SEQUENCE
• In TRAP sequence, one twin develops with a normal phenotype, while the
second twin develops abnormally with a broad spectrum of appearances
• At one extreme end of the spectrum, the entire fetus may be amorphous,
while at the other end, there can be quite well-developed and recognizable
structures, particularly the spine and lower extremities.
• A rudimentary heart that contracts irregularly may sometimes also be
present; hence, the nomenclature of acardiac twinning is not favored.

• The hallmark finding is that blood flow in the umbilical artery of the
abnormal twin is reversed- it flows toward the twin, not toward the placenta.
• The abnormal twin is entirely perfused by the normally developed co-twin,
referred to as the pump twin.
• The TRAP sequence fetus blood supply comes from direct arterio-arterial
and veno-venous connections, with the pump twin in a steal-like
phenomenon.

• Normal umbilical arterial flow is away from the fetus, carrying deoxygenated
blood toward the placenta for replenishment.
• The umbilical arterial flow is directed from the pump twin into the abnormal
fetus.
• The blood then leaves the TRAP sequence twin through the umbilical vein
and bypasses the placenta, returning to the pump twin in a further
deoxygenated state.

• There is 100% non-survival of the abnormal twin, but persistent perfusion
allows it to grow, and the larger it gets the more negative impact it has on the
pump twin.
• Negative impact on the pump twin results from the high output state , which
can lead to congestive heart failure, intrauterine fetal demise ,
polyhydramnios, premature rupture of membranes, and preterm labor.

IMAGING TRAP SEQUENCE
• A detailed anatomic survey should be performed for the pump twin.
• Evidence of strain to the pump twin includes :
- enlargement of the heart
- abnormal contractility
- hydrops.

• Doppler US of the pump twin should include evaluation of the
-umbilical artery
- MCA
-ductus venous.
• In the setting of high-output cardiac failure, the ductus venous waveform
can become abnormal and progress from deepening to absence to eventual
reversal of the A wave.

• US evaluation of the TRAP sequence twin includes an assessment of the
morphology, with documentation of recognizable structures.
• The TRAP sequence twin volume is calculated based on the measurements
obtained in three orthogonal planes.

• In some cases, auto-infarction occurs, and there is no demonstrable flow into
the anomalous twin.
• These cases have a favorable prognosis, as there is no longer any strain on
the pump twin, and such cases can progress to term.

TRAP SEQUENCE MANGEMENT
• When the TRAP sequence twin is small, there is almost uniform survival of
the pump twin with expectant management only.
• In MC-DA pairs, survival is 100%.
• Expectant management can be used when the volume of the TRAP
sequence twin is less than 50% of that of the pump twin.

• Treatment is aimed at stopping blood flow to the abnormal twin.
• Options include open hysterotomy, fetoscopic ligation, selective delivery,
laser or microwave coagulation techniques, alcohol or radiofrequency
ablation and high-intensity focused US (HIFU)

• Radiofrequency ablation is the most widely performed treatment procedure.
• Complications include hematoma, chorio-amniotic separation, shredded
membranes, premature labor, premature rupture of the membranes,
oligohydramnios, and thermal injury.

SELECTIVE FETAL GROWTH
RESTRICTION
• When the smaller twin meets the criteria for growth restriction, this is
referred to as sFGR.
• It occurs in both DC and MC twin pregnancies but is more concerning in
the MC twins because demise of the smaller twin has potentially catastrophic
consequences for the larger twin.
• Unequal placental sharing is thought to be the cause of sFGR in MC twins.

RESTRICTION
• Discordant cord insertions (eg, central vs velamentous, or velamentous vs
marginal) correlate with weight discordance.
• Velamentous cord insertion in one or both twins has been shown to increase
adverse outcomes, including TTTS in MC twin pregnancies.

CRITERIA FOR DIAGNOSIS OF sGFR

• Once the diagnosis of sFGR is established in MC twins, umbilical artery
Doppler US findings in the smaller twin are used for further classification.

RESTRICTION
• Additionally, as with any fetus affected by growth restriction, altered
cerebroplacental ratio, or brain sparing, may be observed.
• In this case, the systolic-to-diastolic ratio as measured at MCA Doppler US
becomes less than that of the umbilical artery.
• This reflects that the brain is being perfused preferentially over the rest of
the body. The prognosis varies with subtype

RESTRICTION
• Type 1 sFGR can be managed expectantly.
• There is a potential role for fetal intervention with either attempted laser
dichorionization of the placenta or selective reduction of the smaller twin.

RESTRICTION
• There is overlap between sFGR and TTTS.
• In the latter the observation of oligohydramnios in the donor and
polyhydramnios in the recipient is the hallmark finding.
• There may or may not be sFGR of the donor or abnormal Doppler US
findings in higher grades.
• In sFGR, the smaller twin may have oligohydramnios but the normally
grown twin has normal fluid volume.

IN UTERO TWIN DEMISE
• When one MC twin dies in utero in the second or third trimester, the
surviving twin has a high likelihood of death and severe cerebral injury.
• This occurs because of acute exsanguination into the low-pressure system of
the dead twin.
• Expectant management is preferred, as the damage occurs at the time of co-
twin demise.
• First-trimester co-twin demise does not cause similar adverse consequences
as does demise in the second trimester or later.

CONJOINED TWINS
• The rarest complication of monochorionic pregnancy is conjoined twins.
• Advances in ultrasound mean that conjoined twins are most identified in the
first trimester.
• Many parents will opt for termination of pregnancy in view of the high risk
of morbidity and mortality in an ongoing pregnancy.
• The prognosis is ultimately determined by the degree and site of the junction
between the twins, and therefore detailed ultrasound studies are necessary to
fully explore the nature of the connections between the twin pair.

CONJOINED TWINS
• The most common site of union is at the thorax with the twins facing each
other, and bowels, liver and hearts may be shared.
• Mapping blood vessels and structures can help plan postnatal surgery.
• When delivery is planned, it should be by caesarean section in a unit
equipped to meet the surgical needs of the babies.

• Renal and liver cysts -ADPKD

• Urinary bladder diverticulum

ULTRASOUND IN TWIN PREGNANCY.pptx

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to ULTRASOUND IN TWIN PREGNANCY.pptx

Similar to ULTRASOUND IN TWIN PREGNANCY.pptx (20)

Recently uploaded

Recently uploaded (20)

ULTRASOUND IN TWIN PREGNANCY.pptx