PU Multiple Gestation Ultrasound 3

Question 1

The 'stuck twin' appearance on ultrasound in TTTS refers to which specific finding?

Accepted Answer

The donor twin tightly wrapped against the uterine wall due to severe oligohydramnios

Answer

One twin showing absent cardiac motion

Answer

Twins whose bodies appear fused on imaging

Answer

One twin fixed in a persistent transverse lie

Question 2

When measuring nuchal translucency (NT) in a twin pregnancy, how should the measurement be performed?

Accepted Answer

Each twin's NT is measured independently and compared to singleton reference ranges

Answer

Add 2 mm to each twin's individual measurement as a twin correction factor

Answer

Only the larger twin's NT is measured to avoid redundancy

Answer

A single combined NT value is calculated for the pair

Question 3

What ultrasound finding definitively differentiates monochorionic-monoamniotic (MCMA) twins from monochorionic-diamniotic (MCDA) twins?

Accepted Answer

Complete absence of any dividing membrane between the twins

Answer

Lambda sign present versus absent

Answer

Presence of the T-sign versus no T-sign

Answer

Differing cord insertion sites on the placenta

Question 4

In dichorionic-diamniotic twins, what is the typical appearance of the inter-twin membrane at the 11–14 week scan?

Accepted Answer

A thick membrane with a wedge of placental tissue (lambda sign) at its insertion

Answer

A very thin single-layer membrane with a T-sign at placental insertion

Answer

No visible membrane in the first trimester

Answer

A membrane showing the T-sign on one side and lambda sign on the other

Question 5

What is the recommended timing of the first ultrasound to optimally determine chorionicity in a newly diagnosed twin pregnancy?

Accepted Answer

As early as possible, ideally before 14 weeks of gestation

Answer

At 16–18 weeks when the membrane is thicker and easier to count

Answer

At the 18–20 week anatomy scan combined with anomaly screening

Answer

Any time during the first half of pregnancy is equally reliable

Question 6

Which complication is unique to monochorionic-monoamniotic twins and is responsible for their significantly elevated perinatal mortality risk?

Accepted Answer

Umbilical cord entanglement causing acute fetal compromise or demise

Answer

Twin-to-twin transfusion syndrome causing hydrops

Answer

Discordant growth leading to selective IUGR

Answer

Increased risk of placenta previa due to large shared placenta

Question 7

In ultrasound surveillance of multiple gestations, discordant growth is standardly defined as an estimated fetal weight difference exceeding what threshold?

Accepted Answer

Greater than 20% based on estimated fetal weight of the larger twin

Answer

Greater than 5% based on abdominal circumference measurements

Answer

Greater than 10% based on biparietal diameter

Answer

Greater than 25% based on femur length discrepancy