Thequestionofwhetherapairoftwinsisidenticalorfraternalisonethatmanyparentsandtwinshave.Ifthetwinsareoppositesex,orverydifferentinappearance(e.g.oneisblondeandblue-eyed,oneisbrunetteandbrown-eyed),thisquestionhasafairlyobviousanswer.However,fraternaltwinscanlookverysimilar,andidenticaltwinscanlookdifferent.Fortwinsfallingintothesecategories,thiscancreatealotofconfusionanduncertaintywhenaskedifthey’reidenticalorfraternal.We’veheardthefollowingstatementsfromtwinswhowerelaterdeterminedtobeidentical:ThedoctortoldourmomthatwearefraternalbecausethereweretwosacsortwoplacentasWelooknothingalikeWeweredifferentsizesatbirthsowecan’tbeidenticalWe’resodifferentwecan’tbeidenticalTwinPregnanciesThenumberofamnioticsacsorplacentaspresentatbirthhasbeenamajorsourceofconfusion,especiallyinoldertwinswhosemotherswouldnothavehadanultrasoundperformedduringpregnancy.However,eveninyoungermothers,dichorionic-diamniotic(di-di)pregnanciesstillcauseuncertaintyintwintype.30%ofdi-dipregnanciesareidenticaltwins,andmanydoctorsstillbelievethatdi-dipregnanciescanonlyresultinfraternaltwins.Thefollowingimageshowsthefourdifferenttypesoftwinpregnancies.Allfourfiguresshowidenticaltwins,butthefirsttwofiguresalsoapplytofraternaltwins,explainingwhytherecanbeconfusioninclassifyingtwinsatbirth.Monochorionic-monoamniotictwinpregnanciesareveryhighrisk,astheyshareaplacentaandanamnioticsac,whichcanresultincordentanglementand/ortwin-to-twintransfusionsyndrome(TTTS).TTTScanresultinsizedifferencesatbirthasbloodflowsunevenlybetweenthetwins.Positioningoftwinswithinthewombcanalsocausesizedifferencesinidenticaltwins.EpigeneticsIdenticaltwinswhoarediscordant(onlyonehasit)forahealthconditionhavehelpedmakecontributionstothegrowingfieldofepigenetics.LivingcreatureshavemillionsofchemicaltagswhichcanattachtoDNA.Thesetagsregulatecellactivity,modifyingtheDNAwithoutchangingtheactualDNAitself,whichinturnaffectsgeneactivity.Thesetagscanbeturnedonoroffbythingssuchasdiet,physicalactivity,stress,sleep,andenvironmentalexposures.Errorsint