Monochorionic twins are identical twins who share one placenta. · Monochorionic-monoamniotic twins are identical twins who share both a placenta and an amniotic ...InthissectionFetalConcernsCenterConditionsProgramsandservicesResourcesPatientstoriesOurlocationOurspecialistsGetasecondopinionResearchandoutcomesFormedicalprofessionalsHome>Medicalcare>FetalConcernsCenter>Conditions>Potentialfetalconditions>BirthdefectsinmonochorionictwinsBirthdefectsandanomaliesinmonochorionictwinsAbirthdefectoranomalyisamedicaltermmeaningirregularordifferentfromnormal.Anomaliesoccurmorefrequentlyinidenticaltwinsthaninotherpregnancies.Whatarethedifferentkindsoftwins?Monochorionictwinsareidenticaltwinswhoshareoneplacenta.Thisoccursinapproximately70percentofpregnancieswithidenticaltwins. Monochorionic-monoamniotictwinsareidenticaltwinswhosharebothaplacentaandanamnioticsac. Monochorionic-diamniotictwinsareidenticaltwinswhoshareaplacentabutnotanamnioticsac. Dichorionictwinseachhavetheirownplacentaandamnioticsac.Thisoccursinapproximately30percentofpregnanciesofidenticaltwins.Allfraternal(non-identical)twinsalsoaredichorionictwins.Problemsthatcanaffectthehealthofmonochorionictwinsinclude: BirthweightdifferencesAmnioticfluidproblems UmbilicalcordentanglementorcompressionTwin-twintransfusionsyndrome(TTTS) Twinreversedarterialperfusionsequence(TRAPsequence) IncreasedriskofbirthdefectsineachtwinPrenataldiagnosisofmonochorionictwinanomaliesDoctorstypicallydetectmonochorionictwinpregnanciesduringaroutineprenatalultrasound.Thebestimagesarevisiblewhenultrasoundsareconductedpriorto14weeksofpregnancy.Thisiswhenthestructuresoftheplacentaandamnioticsacaremostvisible.Theultrasoundwillshowasingleplacentasupplyingbloodflowandtwofetuseswithasingle,thindividingmembraneiftheyaremonochorionictwins.Atthispoint,theultrasoundmayalsoshowifthereisoneamnioticsacortwo.Iftherearetwo,physicianswilllooktoseeiftherearedifferencesintheamountofamnioticfluidpresentineach. Whathappensafterdiagnosis?Dependingontheultrasoundfind