The twin peak sign (also known as the lambda (λ) sign) is a triangular appearance of the chorion insinuating between the layers of the intertwin membrane ...×ArticlesLogInCasesSignUpCoursesQuizDonateAbout×MenuSearchADVERTISEMENT:Radiopaediaisfreethankstooursupportersandadvertisers.BecomeaGoldSupporterandseenoads.ArticlesCasesCoursesLogInLoginSignup{"url":"/signup-modal-props.json?lang=us\u0026email="}ArticlesCasesCoursesQuizAboutRecentEditsGoad-freeSearchTwin-peaksign(twinpregnancy)AssocProfCraigHacking◉◈andAssocProfFrankGaillard◉◈etal.Thetwinpeaksign (alsoknownasthelambda(λ) sign) isatriangularappearanceofthechorion insinuatingbetweenthelayersoftheintertwinmembrane andstronglysuggestsadichorionictwinpregnancy. Itisbestseeninthefirsttrimester(between10-14weeks) 5.Whilethepresenceofatwinpeaksignisausefulindicatorofdichorionicity,itsabsence,however,isnotthatusefulinconfidentlyexcludingit.Itshouldbenotedthatthe'twin'in'twin-peak'refersnottothepresenceoftwopeaks,butthatitrelatestotwins.Inpregnancieswithmorethantwofetuses,thechorionicityandamnionicityofeachfetusmaybedifferent,andthereforethissignonlyaidsindeterminingchorionicityofadjacenttwins.SeealsoTsign:referstotheappearanceoftheinter-twinmembraneinamonochorionictwinpregnancy lambdasignofsarcoidosisQuizquestions{"containerId":"expandableQuestionsContainer","displayRelatedArticles":true,"displayNextQuestion":true,"displaySkipQuestion":true,"articleId":2232,"mcqUrl":"https://radiopaedia.org/articles/twin-peak-sign-twin-pregnancy/questions/2175?lang=us"}References1.WeisslederR,WittenbergJ,HarisinghaniMG.Primerofdiagnosticimaging.MosbyInc.(2007)ISBN:0323040683.ReaditatGoogleBooks-FinditatAmazon2.NybergDA,McGahanJP,PretoriusDH.Diagnosticimagingoffetalanomalies.LippincottWilliams&Wilkins.(2003)ISBN:0781732115.ReaditatGoogleBooks-FinditatAmazon3.TropI.Thetwinpeaksign.Radiology.2001;220(1):68-9.Radiology(fulltext)-Pubmedcitation4.MerzE.Ultrasoundinobstetricsandgynecology,Gynecology.ThiemePublishingGroup.(2007)ISBN:3137544025.