T sign
Ultrasound finding indicating monochorionic twin pregnancy, showing thin membrane insertion perpendicular to the placental surface without triangular tissue projection.
Full Definition
A sonographic marker used to identify monochorionic twins, characterized by the perpendicular insertion of the inter-twin membrane into the placental surface without the triangular placental tissue projection seen in the lambda sign. The membrane appears as a thin line creating a 'T' shape at its placental insertion point. This finding indicates that the twins share a single placenta and chorion, requiring intensive monitoring for twin-to-twin transfusion syndrome and other monochorionic complications. The T sign becomes more apparent as pregnancy progresses and the lambda sign disappears in truly monochorionic pregnancies.
Usage
Usage note: Distinguish from 'lambda sign' which indicates dichorionicity.
In Context
- "The T sign confirmed monochorionic twins, necessitating referral to the fetal medicine unit." — Obstetric consultation
- "Serial scans showed persistent T sign appearance throughout the second trimester." — Follow-up documentation