Monoamniotic twins are identical twins that share an amniotic sac, the fluid-filled sac that holds the baby during pregnancy (also known as the “bag of ...JumptonavigationCOVID-19Updates:Getthelatestonvaccineinformation,in-personappointments,videovisitsandmore.LearnMore>>MainmenuTexasChildren’sFetalCenterPhone:832-822-2229or877-338-2579|ReferralFax:832-824-7333YouarehereHome»TexasChildren’sFetalCenter»ConditionsWeTreat»MonoamnioticTwinsTexasChildren’sFetalCenterMonoamnioticTwinsMonoamnioticTwinsOverviewMonoamniotictwinsareidenticaltwinsthatshareanamnioticsac,thefluid-filledsacthatholdsthebabyduringpregnancy(alsoknownasthe“bagofwaters”).Normally,identicaltwinseachhavetheirownamnioticsac.Monoamniotictwinsareararetypeof“monochorionic”twins,meaningtheyalsoshareaplacenta.Theyaresometimesreferredtoasmonochorionic-monoamniotictwins,ormonoamnioticforshort.Twinsthatsharebothanamnioticsacandaplacentafaceincreasedriskscomparedtoothertwinpregnancies,withthepotentialforseverecomplications–includingumbilicalcordentanglementorcompression–thatcanthreatenthesurvivalofoneorbothbabies.Theseuncommonpregnanciesareestimatedtooccurinonly1percentofidenticaltwinpregnancies.DiagnosisEarlydiagnosisofmonoamniotictwinsisvitaltorecognizingtheuniquerisksassociatedwiththesepregnancies,ensuringclosemonitoringforearlydetectionofcomplications.Thediagnosisistypicallymadeduringaroutineprenatalultrasoundinthefirsttrimesterthatshowsasingleamnioticsaccontainingtwofetuses.Insomecasestheultrasoundmayshowthetwins’umbilicalcordsareentangled,anindicationthefetusesshareasingleamnioticsac.Inthesecases,theimagingshouldalsodetectasharedplacenta.Amisdiagnosisofmonoamniotictwinssometimesoccursearlyinatwinpregnancybecausethemembranethatseparatestwoamnioticsacsissothinitmaynotbevisible,givingtheappearanceofasinglesac.Afollow-upultrasoundthatdetectsthedividingmembranewillrevealthetwinsareintwoseparatesacs,changingthediagnosisto“diamniotic”twins(twoamnioticsacs).Transvaginalultrasonographymaybeneededtoconfirmthediagnosi