A woman at 12 weeks of gestation with twins shows a single placental mass on ultrasound. The intertwin membrane inserts directly into the placenta without any triangular projection of chorionic tissue at its base. This 'T' sign indicates:

• A Dichorionic-diamniotic twins
• B Conjoined twins
• C Monochorionic-monoamniotic twins
• D Monochorionic-diamniotic twins ✓

Explanation

The lambda or twin peak sign, a triangular wedge of chorion extending between the layers of the intertwin membrane, identifies dichorionic twins. Its absence, giving a thin membrane meeting the placenta as a 'T', indicates monochorionic placentation, almost always diamniotic before the second trimester. Monoamnionicity requires failure to visualize any dividing membrane, not merely a T sign.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.