Monochorionic monoamniotic twinning: Occurs when twins share both inner and outer membrane and therefore have no dividing membrane. These cases have all of the ...InthissectionFetalConcernsCenterConditionsProgramsandservicesResourcesPatientstoriesOurlocationOurspecialistsGetasecondopinionResearchandoutcomesFormedicalprofessionalsCongenitalDiaphragmaticHernia:FromdiagnosistodeliveryandbeyondDiagnosisandmanagementofmonochorionic-diamniotictwinsCutting-edgeheartcarebeginsbeforebirthOnthevanguardofbestpracticesingastroschisisSequencingthegenometoaddresspediatricabnormalitiesanddiseaseWombwithaviewHome>Medicalcare>FetalConcernsCenter>Fetalconcernscenterformedicalprofessionals>Diagnosisandmanagementofmonochorionic-diamniotictwinsDiagnosisandmanagementofmonochorionic-diamniotictwinsWrittenbyErikaPeterson,MDMonochorionic-diamniotictwinsaccountforapproximately20%ofspontaneoustwinsandapproximately4%oftwinsconceivedbyartificialreproductivetechniques.Confirmationofthechorionicityoftwinsisimportantasthereareuniquepotentialcomplicationsofmonochorionictwins,andthemanagementandultrasoundsurveillanceisdifferentthanthatofdichorionictwins.Monochorionictwinsareknowntohaveahigherriskofpregnancycomplicationswhencomparedtodichorionictwins.Risksexclusivetomonochorionictwinsinclude:Discordanceofstructuraldefects:TheoverallriskofstructuraldefectsishigherinMCtwins(8%)comparedtoDCtwins(3%)andthereisa5%riskofcongenitalcardiacdefects.Thepresenceofthesedefectscanalsobemorecomplicatedwithmonochorionictwinsasthereisanincreasedriskofcomplicationstothenormalfetus.Selectiveintrauterinegrowthrestriction(IUGR):UnequalplacentalsharingcanleadtoriskofIUGRinonetwin.Thisoccursin10-ˇ15%ofmonochorionictwins.RiskoffetaldemiseduetoIUGRismorecomplicatedduetoplacentalvascularconnectionsthatcanleadeithertodemiseorneurologicinjuryoftheothertwin.Twin-twintransfusionsyndrome(TTTS):Occursinabout10%ofmonochorionictwinsandaccountsforthemajorityofthemorbidityandmortalityofMCtwins.Thepathophysiologyisnotentirelyclear,butit