Conjoined Twins

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hilton-sistersConjoined twins, otherwise known as Siamese twins, are probably the most well known sideshow performer of the past. Famous examples include the original ‘Siamese’ twins, Chang & Eng Bunker, and film stars Daisy & Violet Hilton. Due to advances in surgical techniques, many twins can now be separated at birth, although unfortunately, death is still common.

Types
There are quite a few types of conjoined twins, some more common than others:

Cephalopagus – Part of the upper body is joined, and the heads are also connected, with the faces on opposite sides. This is an extremely rare type.
Craniopagus – Skulls are conjoined, and two seperate brains are fused. About 2% of cases, although some are now successfully separated.
Craniothoracopagus – Twins joined at the head and chest, with only one brain and fused hearts and gastrointestinal tracts
Dicephalus – A single body, but two separate necks and heads. Usually both brains can control the shared body. Example: Brittany and Abigail Hensel
Fetus in Fetu – An undeveloped fetus is contained inside the body of its developed twin.
Ischopagus – Connection of the lower half of the body, usually the coccyx and sacrum. Around 6% of conjoined twins.
Omphalopagus – Twins are joined from the waist to the breastbone. This is the second most common type, around 30%.
Parasitic Twin – One of the twins is smaller, underdeveloped and deformed, and is dependent on its developed sibling.
Parapagus/Diprosopus – Connection of the lower half extending various distances upwards. Around 5% of all conjoined twins.
Pygopagus – Common type in which the twins are connected at the posterior at the rump. 20% of all cases are this type.
Thoraco-Omphalopagus – A combination of Thoracopagus and Omphalopagus.
Thoracopagus – The most common type, making up around 40% of all cases. Connection is at the chest, and often involves sharing the heart, thus survival of both past infancy is very unlikely.

Other Facts
-Conjoined twins occur when a single fertilized ovum doesn’t separate properly. As they are from the same egg, the twins are always identical. Conjoined twins cannot occur when the twins come from separate eggs.
-They are most often female, at a ratio of 3:1.
-They are most likely to occur in India and Africa.
-Occurance is 1 in every 200,000 live births.
-No documented cases of conjoined triplets or quads exist.
-Conjoined twins have been artificially created in amphibians.
-Genetic and environmental conditions are the main influences on the creation of conjoined twins.

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