T sign (obstetrics)

Last revised by Joshua Yap on 12 May 2023

The T sign is really the absence of a twin peak sign (or lambda (λ) sign) and is used in ultrasound assessment of a multifetal pregnancy.

It refers to the lack of chorion extending between the layers of the intertwin membrane, denoting a monochorionic pregnancy. The intertwin membrane comes to an abrupt halt at the edge in a T configuration.

NB: This is not to be confused with the T sign on elbow MRI or the tau sign of a persistent primitive trigeminal artery.

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