Identical twins physically connected in any way are said to be conjoined.

Conjoined Twins are rare, occurring roughly once out of every 200,000 live births. Most commonly found in India or Africa, it is believed that conjoined twins are caused by genetic and environmental conditions which prevent the separation of twins after the 13th day after fertilization. The survival rate of conjoined twins is between 5% and 25%.

The first recorded conjoined twins were Mary and Eliza Chulkhurst, Pygopagus twins born in 1100 in Kent, England.

There are no documented cases of conjoined triplets or quadruplets.

Types of Twinning

Conjoined twins are classified by how they are joined -- the Greek word, pagos, means, 'that which is fixed'.

Conjunctions Not Involving the Heart or Umbilicus

Craniopagus Twins: Twins of these type are joined at the cranium (the top of the head or skull). Craniopagus Twinning occurs in only 2% of all conjoined twin cases and is a very difficult type of twin to separate. Nida and Hira Jamal of Pakistan were of this type.

Pygopagus Twins: Twins of these type are positioned back-to-back with a posterior connecton at the rump. Pygopagus Twinning occurs in roughly 20% of all documented cases. Rosa and Josepha Blazek of what's now the Czech Republic were of this type.

Conjunctions Involving the Umbilicus

Thoraopagus Twins: These twins share part of the chest wall and a heart. Thoraopagus Twinning is the most common of all conjoined twins, occuring in roughly 35% of all reported cases.

Cephalopagus Twins: These twins posess an anterior union of the upper half of the body with two faces on opposite sides of a conjoined head (the heart is sometimes involved). This condition is extremely rare. Twins exhibiting both Thoraopagus and Cephalopagus properties are referred to as Epholothoracopagus.

Parapagus (or Diprosopus) Twins: These twins posess a lateral union of the lower half of the body, extending variable distances upward. This type of twinning accounts for about 5% of all conjoined twins. The heart sometimes involved. Abigail and Brittany Hensel of the United States, sharing a single body from the chest down, are an example of this very rare type of twinning.

Ischiopagus Twins: These twins are joined at the base of the spine (either above or below the coccyx) and make up roughly 6% of all conjoined twins.

Omphalopagus Twins: These are joined from the waist to the lower breastbone and account for about 34% of all reported conjoined cases.

Very Rare Conjunctions

Parasitic Twins: This type of conjunction involves asymmetrical conjoined twins, one twin being smaller, less formed, and dependent upon the other.

Fetus in fetu: This type of twinning involves an imperfect fetus contained completely within the body of its sibling.


Types of Conjoined Twins

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