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Siamese twins

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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When the early embryo divides, but incompletely, some form of conjoined twin is formed. They are always uniovular, and have one amnion, one chorion and one placenta.

There are many different types:

  • thoracopagus - twins joined by the sternum
  • pygopagus - joined by pelvis
  • craniopagus - joined by head

The degree of shared tissue may involve only skin at one extreme or whole organs at the other extreme. Siamese twins are connected by a common liver bridge.

Conjoined twins may be separated if they have no vital parts in common.

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