MZ twins result in 33% DCDA, 66% MCDA, 1% MCMA, although all MCDA twins and MCMA twins are MZ. DZ twins are created from more than one oocyte during​ ...PrintNavigationTop...IntroductionChorionicityAndAmnionicityZygosityFactorsAssociatedWithMultipleGestationConclusionAcknowledgmentsReferencesThischaptershouldbecitedasfollows:Mackie,F,Morris,R,etal,Glob.libr.women'smed.,(ISSN:1756-2228)2016;DOI10.3843/GLOWM.10486Thischapterwaslastupdated:October2016MultipleGestation:biologyandepidemiologyAuthorsFionaL.Mackie,MBChB,MResClinicalResearchFellowinObstetricsandGynaecology,CentreforWomen’sandNewborn’sHealth,UniversityofBirmingham,BirminghamWomen’sHospital,Birmingham,UKR.KatieMorris,MRCOG,PhDSeniorClinicalLecturer/ConsultantMaternalFetalMedicine,CentreforWomen’sandNewborn’sHealth,UniversityofBirmingham,BirminghamWomen’sHospital,Birmingham;WestMidlandsFetalMedicineCentre,BirminghamWomen’sHospital,Birmingham,UKMarkD.Kilby,DSc,MD,FRCOG,FRCPIProfessorofFetalMedicine,CentreforWomen’sandNewborn’sHealth,UniversityofBirmingham,BirminghamWomen’sHospital,Birmingham;WestMidlandsFetalMedicineCentre,BirminghamWomen’sHospital,Birmingham,UKINTRODUCTIONMultiplegestationsareoccurringmorefrequentlyasaresultofincreasinguseofassistedreproductivetechnologies(ART),delayingpregnancy,increasingmaternalageandimmigration.InEnglandandWalesin2014,1.60%ofallmaternities(includinglivebirthsandstillbirths)wereamultiplebirth(seeFigure1).1Thisequatesto10,839womendeliveringtwins,148womendeliveringtriplets,andtwowomendeliveringquadsorabove,outofthe695,233livebabieswhichweredeliveredinEnglandandWales.Therehasthusbeenanincreaseinprevalenceovertime.1Figure1Maternitieswithmultiplebirthsper1000totalmaternitiesinEnglandandWalesin2014accordingtomaternalageatconception1    Therateofallmultiplebirthshasrisencomparedto1.56%in2011,and0.96%in1976.Thisnumberwillbeanunderestimateoftheactualrateofmultiplepregnancyconceptionsowingtothehighnumberofunrecognisedfirsttrimestermiscarriagesofmultiplepregnancies,andsocalled“vanishin