The rate of survival of at least one fetus is close to 75% and almost 40% of both twins. The overall frequency of neurological impairment is around 4% [81].Openaccesspeer-reviewedchapterMonochorionicTwinPregnancy—PotentialRisksandPerinatalOutcomesByJulioElitoJúnior,EduardoFélixMartinsSantanaandGustavoNardiniCecchinoSubmitted:May21st2014Reviewed:August18th2014Published:February4th2015DOI:10.5772/58951Home>Books>ContemporaryGynecologicPracticeAdvertisementDownloaded:4153AdvertisementchapterandauthorinfoAuthorsJulioElitoJúniorDepartmentofObstetrics,UniversidadeFederaldeSãoPaulo(UNIFESP),HospitalSãoPaulo,SãoPaulo,BrazilEduardoFélixMartinsSantanaDepartmentofObstetrics,UniversidadeFederaldeSãoPaulo(UNIFESP),HospitalSãoPaulo,SãoPaulo,BrazilGustavoNardiniCecchinoDepartmentofObstetrics,UniversidadeFederaldeSãoPaulo(UNIFESP),HospitalSãoPaulo,SãoPaulo,Brazil*Addressallcorrespondenceto:DOI:10.5772/58951FromtheEditedVolumeIntechOpenContemporaryGynecologicPracticeEditedbyAtefDarwishContemporaryGynecologicPracticeEditedbyAtefDarwishShow+1.IntroductionSincethemostancienttimes,mythicalstoriesconcerningtwinsweredescribedbothinreligionandart[1].Examplesoftwingodsandheroesarenumerous:fromthetwinsonsofZeustoRome’sfounders,RomulusandRemus.Suchlegendaryconceptionconnectedtotwinsmaystillbefoundincontemporaryprimitivesocieties[2].Theevolutionofmedicinehasledtoadifferentperceptionofthetwinningphenomenon,withseveralimplicationsfortheobstetriccare[3].Thefrequencyofmultiplepregnancieshasbeenincreasingsincethe1970s.Contributingfactorsincludethewideuseoffertilitydrugsandassistedreproductivetechnologies,alongwithahighernumberofwomengivingbirthatolderages[4].Nevertheless,manyphysiciansstillunderestimatetheadversitiesofmultiplepregnancies.[5].Advertisement2.ImportanceThenumberoftwinshasdoubledandtherateoftwinbirthshasrisenfrom18.9to33.2per1,000birthsintheUnitedStates.RecentdatabrieffromtheNationalCenterforHealthStatisticsstatesthatoneinevery30infantsbornin2009wasatwin.TwinbirthratesincreasedinallUSs