Twin peak sign

The twin peak sign (also known as the lambda sign(λ) sign) is an ultrasound finding thata triangular appearance of the chorion insinuating between the layers of the inter twin membrane and strongly suggests a dichorionic twin pregnancy. It is helpfulbest seen in determiningthe first trimester (between 10-14 weeks). ⁵ While the chorionicitypresence of a multifetal pregnancy. The only absolutetwin peak sign of dizygosity on ultrasound is documentationis a useful indicator of different sex fetuses.

Prenatal diagnosis of chorionicitydichorionicity, its absence however is important as monochorionic pregnancies have increased rates and severity of all types of obstetric complications when compared with dichorionic pregnanciesnot that useful in confidently excluding it.

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 inIn 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 features

The sign describes the triangular appearance of the 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

See also:

• T sign: refers to the appearance of the intertwininter twin membrane in a monochorionic twin pregnancy. The sign should not be confused with the 
• lambda sign of sarcoidosis.