lambda sign
Pronunciation: LAM-da
Ultrasound marker indicating dichorionic twin pregnancy, appearing as a triangular projection of placental tissue into the inter-twin membrane.
Full Definition
A characteristic sonographic finding used to determine chorionicity in twin pregnancies, named for its resemblance to the Greek letter lambda (λ). The sign appears as a triangular wedge of echogenic placental tissue extending into the dividing membrane between twin sacs. Its presence confirms dichorionicity, indicating that each twin has its own placenta and chorion. This distinction is crucial for pregnancy management as dichorionic twins have lower risks of complications compared to monochorionic twins. The lambda sign is most reliably identified in the first trimester and early second trimester.
Usage
Usage note: Sometimes written as 'λ sign' in medical records.
In Context
- "The lambda sign was clearly visible on the 11-week scan, confirming dichorionic twins." — Ultrasound report
- "Absence of the lambda sign suggested monochorionic pregnancy requiring specialized monitoring." — Maternal-fetal consultation