Sometimes a woman's ovaries release two eggs, and two separate sperm fertilise each egg. This forms twins. These twins are called fraternal ...SkiptocontentSkiptonavigationAbouttwinsWeusuallydescribetwinsaccordingto:howmanyeggstheydevelopfrom–oneortwowhethertheysharea placentaintheirmother’swomb.Themaintypesoftwinsare fraternaltwinsand identicaltwins.Mosttwinsarebornhealthy,butatwinpregnancycanmeanahigherchanceofhealthcomplicationsforyouandyourbabies.ifyou'repregnantwithtwins,youandyourbabieswillneedextracheck-ups.FraternaltwinsAllpregnanciesstartwhenaspermfertilisesanegg.Thisfertilisedeggiscalleda zygote.Sometimesawoman’sovariesreleasetwoeggs,andtwoseparatespermfertiliseeachegg.Thisformstwins.Thesetwinsarecalledfraternaltwins,dizygotictwins(meaningtwozygotes)ornon-identicaltwins.Duringpregnancy,thedevelopingbabiesgetoxygenandfoodfromtheirmotherthroughtheplacenta andumbilicalcord.Fraternaltwinshave separateplacentasandumbilicalcords.Thetechnicalnameforthisisdichorionic.Fraternaltwinscanbethesameoroppositesexandtheirgenesareasdifferentasanyotherbrotherandsister.Often,same-sexfraternaltwinslookdifferent–forexample,theymighthavedifferenthairoreyecolour.Occasionallytheylookquitesimilar.Fraternaltwinshappeninabout70%oftwinbirthsinAustralia.Veryrarely,fraternaltwinsshareaplacenta.Thesetypesoftwinsarecalledchimaerictwins.IdenticaltwinsSometimesafertilisedeggsplitswithinafewdaysofconceptiontoproduce geneticallyidenticaltwins.Becausethesetwinscomefromonezygote,theyarealsoknownasmonozygotic.Identicaltwinsarethesamesex.Therearethreetypesofidenticaltwins.Aboutone-thirdofidenticaltwinssplitsoonafterfertilisationandformcompletelyseparatetwins.Likefraternaltwins,thesetwinshave separateplacentas.Theothertwo-thirdssplitaftertheyattachtothewallofthewomb.Asaresult,they shareaplacenta.Thetechnicalnameforthisismonochorionic.Inaverysmallnumberofidenticaltwins,splittingmighthappenevenlater.Inthiscase,bothtwins shareaninnersac,calledtheamnion,inadditiontosharingaplacenta.Thetechnicalnamefo