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

The stuck twin is the TTTS donor, whose severely reduced amniotic fluid causes it to be pressed tightly against the uterine wall, appearing 'stuck' without room to move.

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

Each twin's NT is measured independently using the same singleton reference ranges, as NT performance for aneuploidy screening has been validated using this approach.

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

The complete absence of a dividing membrane confirms MCMA twinning, whereas MCDA twins have a thin but identifiable membrane separating their sacs.

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

The lambda (twin peak) sign in DCDA twins is formed by chorionic villi invading the base of the thick inter-twin membrane, creating a triangular echogenic wedge.

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

Chorionicity should be determined before 14 weeks because the lambda and T-signs are most reliable in the first trimester and become harder to distinguish as pregnancy advances.

PU - Pregnancy Ultrasound Certification Practice Test

PU - Pregnancy Ultrasound Certification Practice Test

PU Multiple Gestation Ultrasound 3