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.
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.
Ultrasound - obstetric
- ultrasound (introduction)
- obstetric ultrasound
first trimester and early pregnancy
- gestational sac
- yolk sac
- Beta-hCG levels
- ectopic pregnancy
- multiple gestations
- subchorionic hematoma
- failed early pregnancy
- nuchal translucency
- chorionic villus sampling (CVS) and amniocentesis
- second trimester
- first trimester and early pregnancy
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- 3. Trop I. The twin peak sign. Radiology. 2001;220 (1): 68-9. Radiology (full text) - Pubmed citation
- 4. Merz E. Ultrasound in obstetrics and gynecology, Gynecology. Thieme Publishing Group. (2007) ISBN:3137544025. Read it at Google Books - Find it at Amazon
- 5. Fong KW, Toi A, Salem S et-al. Detection of fetal structural abnormalities with US during early pregnancy. Radiographics. 24 (1): 157-74. doi:10.1148/rg.241035027 - Pubmed citation
Synonyms & Alternative Spellings
|Synonyms or Alternative Spelling||Include in Listings?|
|twin peak sign||✗|
|Lambda sign of twin pregnancy||✓|
|Twin-peak sign in a twin pregnancy||✗|