Twin Statistics

Currently in the UK it is thought that around 33% of twins are Monozygotic (’identical’) and around 66% are Dizygotic (’non identical’ or ‘fraternal’)

Monozygotic Twins (normally referred to as Identical or ‘ Id’ or sometimes ‘MZ’). Mono means ‘from one’ so Monozygotic twins started off as one fertilized egg (zygote) which split in the first few days to a week or so after conception. Monozygotic twins are the same sex* and generally look very alike, hence the label ‘identical’.

Of the Monozygotic (’identical’ ) Twins 33% are Dichorionic Diamniotic (i.e. NOT sharing a placenta or an outer membrane (chorion)  This is sometimes abbreviated to DC/DA  . This occurs because the fertilized egg split before the chorion had formed, in the first 3 days after conception. Depending how close together the twins implant into the uterus, they may have a fused placenta or or may have individual placentas.

Therefore it is possible for same sex twins to be identical and NOT share a placenta or chorion or amniotic sac66% of Monozygotic Twins are sharing an outer membrane (chorion) but have individual amniotic sacs. This is known as Monochorionic Diamniotic sometimes abbreviated to MC/DA  These have split between days 3 and 9 after conception.

1% of Monozygotic Twins are sharing both a chorion and amniotic sacs. These are known as Monochorionic Monoamniotic. This is sometimes abbreviated to MC/MA Monochorionic monoamniotic twins split after day 9  will be monochorionic monoamniotic.

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One Comments

  • Archana singh

    December 8, 2014

    We are identical twin sisters.very good to read about as given in article.we both are very close to each other but as we are married we live at differen places connected by phone Facebook.we love each other very much.


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