This site is targeted at medical and radiology professionals, contains user contributed content, and material that may be confusing to a lay audience. Use of this site implies acceptance of our Terms of Use.

Twin-peak sign

The twin peak sign (also known as the lambda sign) is an ultrasound finding that is helpful in determining the chorionicity of a multifetal pregnancy. The only absolute sign of dizygosity on ultrasound is documentation of different sex fetuses.

Prenatal diagnosis of chorionicity is important as monochorionic pregnancies have increased rates and severity of all types of obstetric complications when compared with dichorionic pregnancies.

It should be noted that the 'twin' in 'twin-peak' refers not to the presence of two peaks, but that it relates to twins. Also important to realise is that in pregnancies with more than two fetuses, the chorionicity and amnionicity of the each fetus may be different, and therefore this sign only aids in determining chorionicity of adjacent twins.

Radiographic assessment

The sign describes the triangular appearance to chorion insinuating between the layers of the inter twin membrane and strongly suggests a dichorionic twin pregnancy. It is best seen in the first trimester (between 10-14 weeks 5). While the presence of a twin peak sign is a useful indicator of dichorionicity, its absence however is not that useful in confidently excluding it.

In contrast the T sign refers to the appearance of the intertwin membrane in a monochorionic twin pregnancy. The sign should not be confused with the lambda sign of sarcoidosis.

Updating… Please wait.
Loadinganimation

Alert_accept

Error Unable to process the form. Check for errors and try again.

Alert_accept Thank you for updating your details.