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Twin pregnancies

Twins account for about 1% of all pregnancies with two-thirds being dizygotic (non-identical) and one-third monozygotic (identical)

  • In non-identical twins each fetus has its own placenta and amniotic sac (dichorionic, diamniotic).
  • In identical twin pregnancies there may be sharing of the same placenta (monochorionic), amniotic sac (monoamniotic) or even fetal organs (conjoined or Siamese). One-third of identical twins are dichorionic and two-thirds are monochorionic
  • Therefore, all monochorionic twins are identical and 6 out of 7 dichorionic twins are non-identical